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December 19, 2016 | https://www.sciencedaily.com/releases/2016/12/161219085710.htm | Above and beyond megathrusts: Draining pore-fluids dampens tremors | In the Nankai subduction zone, Japan, non-volcanic deep tremors occur down-dip of the megathrust seismogenic zone, and are observed to coincide temporally with short-term slow-slip events (SSEs). They occur within a limited depth range of 30-35 km over an along-strike length of ~700 km, associated with subduction of the Philippine Sea Plate. As Low-Frequency Earthquakes (LFEs) coincide spatially with tremor activity, the locations of LFEs act as a proxy for tremor activity. There are two distinct gaps in LFE activity at the Kii Gap and Ise Gap, while there is limited or no LFE activity beneath Kanto and Kyushu at the extensions of the LFE activity zone. Junichi Nakajima from Tokyo Institute of Technology and Akira Hasegawa at Tohoku University examined the seismic properties of Nankai, including areas where LFEs are present and absent, in an effort to elucidate the factors controlling LFE generation. | The observed P-wave (dVp) and S-wave (dVs) velocities show the presence of low-velocity anomalies in the overlying plate at Kanto, Ise Gap, Kii Gap, and Kyushu, where there is limited or no LFE activity. LFEs do not occur on the megathrust where dVp and dVs are lower than approximately -4%, suggesting a systematic change in seismic velocities in the overlying plate between areas with and without LFE activity. There is a spatial correlation between LFE locations and seismic velocity, attenuation, and anisotropy anomalies. One hypothesis that could explain the variation in seismic properties along the LFE band is along-strike variation in the degree of prograde metamorphism above the megathrust that is proportional to the rate of fluid leakage from the subducting slab into the overlying plate. Notably, large amounts of fluid are liberated from the subducting crust at depths of 30-60 km.The along-strike variations in seismic properties suggest that the overlying plate is less metamorphosed in areas with LFE activity, and is significantly metamorphosed in areas of limited or no LFE activity. This anti-correlation between LFEs and metamorphism is probably caused by along-strike variation in hydrological conditions in the overlying plate. An impermeable overlying plate restricts fluids to the megathrust, whereas fluids escape from the megathrust, if the overlying plate is permeable. Undrained conditions at the megathrust elevate pore-fluid pressures to near-lithostatic values, lower the shear strength of the megathrust sufficiently to facilitate LFEs, and result in a low degree of metamorphism in the overlying plate. In contrast, in areas of limited LFE activity, fluids migrate into and metamorphose the permeable overlying plate, reducing pore-fluid pressures at the megathrust, which is no longer weak enough to generate LFEs.The large number of crustal earthquakes in the Kii Gap and Ise Gap suggests that LFE activity and seismicity in the overlying plate are anti-correlated, largely reflecting the magnitude of fluid flux from the megathrust. The scientists concluded that a well-drained megathrust allows fluids to migrate into the overlying plate, inhibiting LFE activity at the megathrust, but facilitating shallow seismicity due to the decreased shear strength of crustal faults. | Earthquakes | 2,016 |
December 15, 2016 | https://www.sciencedaily.com/releases/2016/12/161215143532.htm | Underwater volcano's eruption captured in exquisite detail by seafloor observatory | The cracking, bulging and shaking from the eruption of a mile-high volcano where two tectonic plates separate has been captured in more detail than ever before. A University of Washington study published this week shows how the volcano behaved during its spring 2015 eruption, revealing new clues about the behavior of volcanoes where two ocean plates are moving apart. | "The new network allowed us to see in incredible detail where the faults are, and which were active during the eruption," said lead author William Wilcock, a UW professor of oceanography. The new paper in The studies are based on data collected by the Cabled Array, a National Science Foundation-funded project that brings electrical power and internet to the seafloor. The observatory, completed just months before the eruption, provides new tools to understand one of the test sites for understanding Earth's volcanism."Axial volcano has had at least three eruptions, that we know of, over the past 20 years," said Rick Murray, director of the NSF's Division of Ocean Sciences, which also funded the research. "Instruments used by Ocean Observatories Initiative scientists are giving us new opportunities to understand the inner workings of this volcano, and of the mechanisms that trigger volcanic eruptions in many environments."The information will help us predict the behavior of active volcanoes around the globe," Murray said.It's a little-known fact that most of Earth's volcanism takes place underwater. Axial Volcano rises 0.7 miles off the seafloor some 300 miles off the Pacific Northwest coast, and its peak lies about 0.85 miles below the ocean's surface. Just as on land, we learn about ocean volcanoes by studying vibrations to see what is happening deep inside as plates separate and magma rushes up to form new crust.The submarine location has some advantages. Typical ocean crust is just 4 miles (6 km) thick, roughly five times thinner than the crust that lies below land-based volcanoes. The magma chamber is not buried as deeply, and the hard rock of ocean crust generates crisper seismic images."One of the advantages we have with seafloor volcanoes is we really know very well where the magma chamber is," Wilcock said."The challenge in the oceans has always been to get good observations of the eruption itself."All that changed when the Cabled Array was installed and instruments were turned on. Analysis of vibrations leading up to and during the event show an increasing number of small earthquakes, up to thousands a day, in the previous months. The vibrations also show strong tidal triggering, with six times as many earthquakes during low tides as high tides while the volcano approached its eruption.Once lava emerged, movement began along a newly formed crack, or dike, that sloped downward and outward inside the 2-mile-wide by 5-mile-long caldera."There has been a longstanding debate among volcanologists about the orientation of ring faults beneath calderas: Do they slope toward or away from the center of the caldera?" Wilcock said. "We were able to detect small earthquakes and locate them very accurately, and see that they were active while the volcano was inflating."The two previous eruptions sent lava south of the volcano's rectangular crater. This eruption produced lava to the north. The seismic analysis shows that before the eruption, the movement was on the outward-dipping ring fault. Then a new crack or dike formed, initially along the same outward-dipping fault below the eastern wall of the caldera. The outward-sloping fault has been predicted by so-called "sandbox models," but these are the most detailed observations to confirm that they happen in nature. That crack moved southward along this plane until it hit the northern limit of the previous 2011 eruption."In areas that have recently erupted, the stress has been relieved," Wilcock said. "So the crack stopped going south and then it started going north." Seismic evidence shows the crack went north along the eastern edge of the caldera, then lava pierced the crust's surface and erupted inside and then outside the caldera's northeastern edge.The dike, or crack, then stepped to the west and followed a line north of the caldera to about 9 miles (15 km) north of the volcano, with thousands of small explosions on the way."At the northern end there were two big eruptions and those lasted nearly a month, based on when the explosions were happening and when the magma chamber was deflating," Wilcock said.The activity continued throughout May, then lava stopped flowing and the seismic vibrations shut off. Within a month afterward the earthquakes dropped to just 20 per day.The volcano has not yet started to produce more earthquakes as it gradually rebuilds toward another eruption, which typically happen every decade or so. The observatory centered on Axial Volcano is designed to operate for at least 25 years. "The cabled array offers new opportunities to study volcanism and really learn how these systems work," Wilcock said. "This is just the beginning." | Earthquakes | 2,016 |
December 15, 2016 | https://www.sciencedaily.com/releases/2016/12/161215085924.htm | Tsunami risk for Florida and Cuba modeled | While the Caribbean is not thought to be at risk for tsunamis, a new study by researchers at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science indicates that large submarine landslides on the slopes of the Great Bahama Bank have generated tsunamis in the past and could potentially again in the future. | "Our study calls attention to the possibility that submarine landslides can trigger tsunami waves," said UM Rosenstiel School Ph.D. student Jara Schnyder, the lead author of the study. "The short distance from the slope failures to the coastlines of Florida and Cuba makes potential tsunamis low-probability but high-impact events that could be dangerous."The team identified margin collapses and submarine landslides along the slopes of the western Great Bahama Bank -- the largest of the carbonate platforms that make up the Bahamas archipelago -- using multibeam bathymetry and seismic reflection data. These landslides are several kilometers long and their landslide mass can slide up to 20 kilometers (12 miles) into the basin.An incipient failure scar of nearly 100 kilometers (70 miles) length was identified as a potential future landslide, which could be triggered by an earthquake that occasionally occur off the coast of Cuba.Using the mathematical models commonly used to evaluate tsunami potential in the U.S., the researchers then simulated the tsunami waves for multiple scenarios of submarine landslides originating off the Great Bahama Bank to find that submarine landslides and margin collapses in the region could generate dangerous ocean currents and possibly hazardous tsunami waves several meters high along the east coast of Florida and northern Cuba."Residents in these areas should be aware that tsunamis do not necessarily have to be created by large earthquakes, but can also be generated by submarine landslides that can be triggered by smaller earthquakes," said UM Rosenstiel School Professor of Marine Geosciences Gregor Eberli, senior author of the study.The study, titled "Tsunamis caused by submarine slope failures along western Great Bahama Bank," was published in the Nov. 4 issue of the journal | Earthquakes | 2,016 |
December 15, 2016 | https://www.sciencedaily.com/releases/2016/12/161215085909.htm | Tectonic shift? Study of olivine provides new data for measuring Earth's surface | Plate tectonics, the idea that the surface of the Earth is made up of plates that move apart and come back together, has been used to explain the locations of volcanoes and earthquakes since the 1960s. | One well-known example of this is the Pacific Ring of Fire, a 25,000-mile stretch of the Pacific Ocean known for its string of underwater volcanoes (nearly 450 of them) and earthquake sites, according to the National Oceanic and Atmospheric Administration (NOAA).On the Pacific Coast, this area sits along the subduction zone known as the Cascadia plate, which runs down the west coast of Canada to the west coast of the United States. Most earthquakes are said to occur at subduction zones or along faults in tectonic plates.What actually defines a tectonic plate and how thick plates are, however, has remained a hotly debated topic. This is because while scientists know that the top of the plate is the surface of the Earth, defining the plate's bottom boundary has been challenging.A recent study by the University of Delaware's Jessica Warren and colleagues at the University of Oxford and the University of Minnesota, Twin Cities, provides a new data set that scientists can use to understand this problem."Understanding the thickness of the plate is important to understanding how plates move around, both when they form at mid-ocean ridges and later on when the material goes back down into the Earth through subduction zones such as those in Cascadia, the Andes, Japan and Indonesia," said Warren, assistant professor in the Department of Geological Sciences in the College of Earth, Ocean, and Environment."It also can help scientists model and predict future earthquake and volcanic hazards, where they might occur and how deep the devastation might be depending on what the models show."To understand what's happening inside the Earth, scientists must be creative because studying the interior of the Earth in situ is impossible.Instead, scientists study how seismic waves pass through the Earth and then invert the signal that is received to reverse engineer what's happening. They also model the thermal properties of the rock, including where temperature changes occur, because they know that the interior of the Earth is hotter than the surface crust."Science has been telling us that what we predict for temperature changes within the Earth should agree with what the seismic waves are telling us. The problem has been that these two models don't agree," said Warren, a petrology expert who studies the origin of rocks and how they formed.One longstanding argument has been whether the Gutenberg discontinuity -- the identification of a change in seismic properties -- represents the bottom of the plate.To investigate this problem, Warren and her colleagues performed laboratory experiments on olivine, the main mineral found in the Earth's mantle (the upper ~250 miles of the planet). Olivine also is the main mineral in peridotite rock, which is considered to be a robust model of the interior of the Earth's composition.The researchers took olivine and added melt (also known as basalt) to mimic how a new plate is created at a mid-ocean ridge. The team then twisted the olivine-melt mixture under high temperatures and high pressure to determine the influence of melt on the alignment of olivine crystals. They then used these experiments to predict the seismic signature of this rock and compared it to the seismic signature associated with the Gutenberg discontinuity.The team's results showed that the Gutenberg discontinuity does not define the bottom of the plate, but instead is caused by the presence of olivine-melt mixtures within tectonic plates."I've spent over a decade studying how olivine minerals are oriented in peridotite rocks because the flow patterns provide a historical record of how these rocks from the mantle have changed and deformed over time," says Warren.The research team's results suggest the best way to model the plate thickness is based on the thermal profile and the conductive cooling that occurs as a plate ages."We think that the bottom of the plate is below where you have a cooling in the temperature profile. It is a layer that is associated with melt being trapped or frozen in the rock and changing the seismic properties in the rock that subsequently produced the layer that we're imaging," she said. "By our estimates, this would mean that the tectonic plates in the ocean are approximately 100 kilometers or about 62 miles thick. "The team's data also offers an explanation for the Guttenberg discontinuity, Warren continued, saying that it corresponds to melt that was trapped or frozen in the rock after melting at mid-ocean ridges, which produced a change in how the seismic waves pass through the rock. | Earthquakes | 2,016 |
December 14, 2016 | https://www.sciencedaily.com/releases/2016/12/161214090308.htm | Quake-detection app captured nearly 400 temblors worldwide | The University of California, Berkeley's worldwide network of smartphone earthquake detectors has recorded nearly 400 earthquakes since the MyShake app was made available for download in February, with one of the most active areas of the world the fracking fields of Oklahoma. | The Android app harnesses a smartphone's motion detectors to measure earthquake ground motion, then sends that data back to the Berkeley Seismological Laboratory for analysis. The eventual goal is to send early-warning alerts to users a bit farther from ground zero, giving them seconds to a minute of warning that the ground will start shaking. That's enough time to take cover or switch off equipment that might be damaged in a quake.To date, nearly 220,000 people have downloaded the app, and at any one time, between 8,000 and 10,000 phones are active -- turned on, lying on a horizontal surface and connected to a wi-fi network -- and thus primed to respond.An updated version of the MyShake app will be available for download Dec. 14 from the Google Play Store, providing an option for push notifications of recent quakes within a distance determined by the user, and the option of turning the app off until the phone is plugged in, which could extend the life of a single charge in older phones."The notifications will not be fast initially -- not fast enough for early warning -- but it puts into place the technology to deliver the alerts and we can then work toward making them faster and faster as we improve our real-time detection system within MyShake," said project leader Richard Allen, a UC Berkeley professor of earth and planetary sciences and director of the seismology lab.In a presentation on Wednesday, Dec. 14, during this week's annual meeting of the American Geophysical Union in San Francisco, UC Berkeley developer and graduate student Qingkai Kong will summarize the app's performance. Ten months of operation clearly shows that the sensitivity of the smartphone accelerometers and the density of phones in many places are sufficient to provide data quickly enough for early warning. The phones readily detect the first seismic waves to arrive -- the less destructive P waves -- and send the information to Berkeley in time to issue an alert that the stronger S wave will soon arrive."We already have the algorithm to detect the earthquakes running on our server, but we have to make sure it is accurate and stable before we can start issuing warnings, which we hope to do in the near future," Kong said.The app can detect quakes as small as magnitude 2.5, with the best sensitivity in areas with a greater density of phones. The largest number of phones to record a quake was 103, after the 5.2 magnitude quake that occurred on the San Jacinto fault near Borrego Springs in San Diego County on June 10. Phones 200 kilometers from the epicenter detected that temblor. The largest quake detected occurred on April 16 in Ecuador: a 7.8 magnitude quake that triggered two phones, 170 and 200 kilometers from the epicenter.Allen, Kong and their colleagues at Deutsche Telekom's Silicon Valley Innovation Center believe the app's performance shows it can complement traditional seismic networks, such as that operated nationally by the U.S. Geological Survey, but can also serve as a stand-alone system in places with few seismic stations, helping to reduce injuries and damage from earthquakes.While the app has detected quakes in seismically active areas such as Chile, Mexico, New Zealand, Taiwan, Japan and the West Coast of the U.S., one surprising hot spot has been the traditionally quiet state of Oklahoma. The practice of injecting oil well wastewater deep underground has activated faults in the area to the extent that the state is rattled hundreds of times a year."Oklahoma is now clearly No. 1 in terms of the number of earthquakes in the lower 48 states," Kong said.Most of Oklahoma's earthquakes are small, but MyShake users in the state, which number only about 200, easily detected the Sept. 3 magnitude 5.8 quake, the strongest ever to hit the state. During that event, 14 phones in the state triggered, but even this relatively small number of phones allowed the seismology lab to peg the magnitude within 1 percent of estimates from ground seismic stations, and located the epicenter to within 4 kilometers (2.5 miles)."These initial studies suggest that the data will be useful for a variety of scientific studies of induced seismicity phenomena in Oklahoma, as well as having the potential to provide earthquake early warning in the future," Kong said.He will summarize the Oklahoma data during a poster session on Friday, Dec. 16.The MyShake app and the computer algorithm behind it were developed by Allen, Kong and a team of programmers at the Silicon Valley Innovation Center in Mountain View, California, which is part of the Telekom Innovation Laboratories (T-Labs) operated by Deutsche Telekom, owner of T-Mobile. Louis Schreier, the leader of that team, co-wrote a paper with Allen and Kong on the first six months of MyShake's observations, published Sept. 29 in the journal | Earthquakes | 2,016 |
December 13, 2016 | https://www.sciencedaily.com/releases/2016/12/161213112341.htm | Mapping New Zealand landslides with satellites, drones, helicopters, hiking boots | A University of Michigan-led team of geologists and engineers is mapping surface ruptures and some of the tens of thousands of landslides triggered by last month's magnitude-7.8 earthquake in New Zealand. | The U-M-led team includes a researcher from the University of Colorado at Boulder. Working in collaboration with scientists from New Zealand's GNS Science and the U.S. Geological Survey, they will combine observations collected by satellites, drones, helicopters and on foot to create what is expected to be the largest inventory of earthquake-triggered landslides, according to team leader and U-M geologist Marin Clark.The high-resolution digital topographic maps the researchers create will help response teams in New Zealand determine which landslides pose the greatest threat for future sliding and for river damming that can lead to catastrophic flooding. The project is also viewed as a training exercise for future large earthquakes anticipated in places like Southern California.The powerful New Zealand quake struck Nov. 13 near the town of Kaikoura, on the east coast of the South Island. It killed two people, generated tsunami waves several feet high and stranded hundreds of tourists who had to be evacuated by helicopter and ship.Current estimates are that 80,000 to 100,000 landslides were triggered by ruptures along at least nine faults. About 150 of the landslides blocked river valleys, and nine are being monitored as potential threats for catastrophic flooding due to river damming."If the 100,000 estimate is correct, then this would be the largest documented earthquake-related landsliding event ever, slightly larger than one that occurred in China in 2008," said Clark, U-M associate professor of earth and environmental sciences."The landslide dams are especially important to recognize immediately after an event like this, while there is still time to do something about them. To avoid a potentially catastrophic breach and flooding event, spillways can be constructed to drain the water."Members of Clark's team went to New Zealand late last month, hiking into the affected region with handheld GPS receivers and using helicopter-based observations and drone imagery to map fault ruptures and landslides. They worked with scientists from GNS Science and the Geotechnical Engineering Extreme Events Reconnaissance Association, a volunteer organization known as GEER.U-M scientists who made the reconnaissance trip were Adda Athanasopoulos-Zekkos, associate professor of civil and environmental engineering, and postdoctoral researcher Timothy Stahl of the Department of Earth and Environmental Sciences, who is also an NSF Postdoctoral Fellow. Clark and team member Dimitrios Zekkos, U-M associate professor of civil and environmental engineering, will travel to New Zealand next month.The U-M-led team uses small, quad-rotor drones fitted with ultra-high-definition cameras to capture extremely detailed video images of the landslides and surface ruptures."Drones have totally changed how our work is done," said Zekkos, who also used the remotely operated aerial vehicles to map landslides in Nepal -- on a team led by Clark -- following last year's magnitude-7.8 earthquake there, which killed more than 8,000 people and created nearly 25,000 landslides."Landslides can block roads, and helicopters are expensive to operate and are often needed for other purposes after a natural disaster," he said. "But you can quickly send a drone into places that would otherwise be practically impossible to see -- and you can get really, really close."On Dec. 8, Clark's team received final approval of funding from the National Science Foundation for the year-long New Zealand study. While the amount of "rapid response funding" is modest at $46,516, the NSF award also gives the researchers access to satellite imagery and supercomputers they will use to create exquisitely detailed before-and-after digital maps.The team's study area spans about 25,000 square miles, a region slightly larger than the state of West Virginia. The researchers will have access to stereoscopic satellite imagery of the sparsely populated, mountainous study area gathered both before and after the Nov. 13 Kaikoura earthquake.The razor-sharp satellite images sample the surface at a 30-centimeter spacing and can recognize objects on the ground as small as 2 meters across, roughly the size of an SUV. In some cases, 1-meter resolution is possible. The pre-quake images were collected by commercial satellite company Digital Globe following New Zealand's 2011 Christchurch earthquake, which killed 185 people."What's unique about this situation is that we've never had high-resolution 'before' imagery that covers the entire area affected by a major earthquake," Clark said.Digital Globe is now collecting "after" images of the region affected by last month's Kaikoura earthquake. Clark's team will have access to both data sets."It's never been done at this scale at this resolution, so this is going to give us an unprecedented view of the details of what's happening on the ground," she said.Multiple satellite observations of the same ground locations from different viewing angles were combined to create stereoscopic imagery that provides a three-dimensional view of the surface. The 3-D view, in turn, enables researchers to precisely measure the elevation of surface features -- including landslides."The 3-D models from satellite observations are not as accurate as drone-created models, but they cover much wider areas and are precise enough to measure any vertical change of more than a few tens of centimeters, or roughly the height of a beach ball," said team member Michael Willis, assistant professor at the University of Colorado.The satellite imagery will be used to create before-and-after digital elevation models, or DEMs, which can be thought of as extremely detailed digital topographic maps. Techniques used to generate high-resolution DEMs from stereoscopic satellite images were developed by Willis as a member of a team creating such models for the Arctic.Knowing the exact elevation at a given point before and after a landslide allows scientists to calculate the volume of material that moved, a value that is critical when trying to assess the threat posed now and in the future, Clark said."Some of these landslide locations are current threats for damming and catastrophic flooding. And all of them are now more susceptible to future landsliding in response to rains," she said. "So by knowing exactly where these landslides are and how far they've traveled, as well as their volume and composition, we can make better predictions about what might happen in the coming weeks, months and years."Data collected on foot and using drones and helicopters will be used to validate the satellite images, a process called ground truthing.The first DEMs based on the "before" images of the affected region could be finished this month and will be provided to landslide response teams from the U.S. Geological Survey and GNS Science. DEMs based on post-quake satellite imagery could take months to complete, depending on weather and other variables.The New Zealand project is viewed as a training exercise for future large earthquakes, including an anticipated Southern California event along the San Andreas Fault. In that case, "before" images along the San Andreas have already been collected using plane-mounted LiDAR, a surveying method that measures distance to a target by illuminating it with laser light.The Nov. 13 New Zealand earthquake resulted from faulting on or near the boundary between the Pacific and Australian tectonic plates. At the location of the magnitude-7.8 earthquake, the Pacific plate is moving west-southwest with respect to the Australian plate at a rate of about 40 millimeters (1.6 inches) per year.The NSF-funded New Zealand project is a collaboration between the University of Michigan and the University of Colorado at Boulder. Clark's team also includes a collaborator from Greece, John Manousakis. | Earthquakes | 2,016 |
December 13, 2016 | https://www.sciencedaily.com/releases/2016/12/161213074527.htm | Earthquake faults are smarter than we usually think | Northwestern University researchers now have an answer to a vexing age-old question: Why do earthquakes sometimes come in clusters? | The research team has developed a new computer model and discovered that earthquake faults are smarter -- in the sense of having better memory -- than seismologists have long assumed."If it's been a long time since a large earthquake, then, even after another quake happens, the fault's 'memory' sometimes isn't wiped out, so there's still a good chance of having another," said Seth Stein, the study's senior author and the William Deering Professor of Geological Sciences in the Weinberg College of Arts and Sciences."As a result, a cluster of earthquakes occurs," he said. "Earthquake clusters imply that faults have a long-term memory."The model shows that clusters can occur on faults with long-term memory, so that even after a big earthquake happens, the chance of another earthquake can stay high. The memory comes from the fact that the earthquake didn't release all the strain that built up on the fault over time, so some strain remains after a big earthquake and can cause another."This isn't surprising," said Bruce D. Spencer, a professor of statistics in Weinberg and an author of the study. "Many systems' behavior depends on their history over a long time. For example, your risk of spraining an ankle depends not just on the last sprain you had, but also on previous ones."Leah Salditch, lead author of the study, will present details of the research Thursday, Dec. 15, at the American Geophysical Union (AGU) meeting in San Francisco.Since earthquake seismology started after a large earthquake destroyed San Francisco in 1906, seismologists have usually assumed that when the next big earthquake will happen on a fault depends on the time since the last one happened. In other words, a fault has only short-term memory -- it "remembers" only the last earthquake and has "forgotten" all the previous ones.This assumption goes into forecasting when future earthquakes will happen, and then into hazard maps that predict the level of shaking for which earthquake-resistant buildings should be designed.However, Salditch, a graduate student in Stein's research group, explained, "Long histories of earthquakes on faults sometimes show clusters of earthquakes with relatively short times between them, separated by longer times without earthquakes. For example, during clusters on the San Andreas, big earthquakes happened only about 50 years apart, while the clusters are separated by several hundred years. Clusters also have been found on the Cascadia fault system off the coast of Oregon, Washington and British Columbia, and along the Dead Sea fault in Israel."These results could be important for forecasting when future earthquakes will happen, said Edward M. Brooks, an author of the study and a graduate student in Stein's research group."When you're trying to figure out a team's chances of winning a ball game, you don't want to look just at what happened in the last game between those teams," Brooks said. "Looking back over earlier games also can be helpful. We should learn how to do a similar thing for earthquakes." | Earthquakes | 2,016 |
December 1, 2016 | https://www.sciencedaily.com/releases/2016/12/161201092817.htm | New study describes 200 million years of geological evolution | 200 million years of geological evolution of a fault in Earth's crust has recently been dated. Published in | Tectonic plates, big sections of Earth's crust and blocks underneath them, are constantly moving. The areas where these sections meet and interact are called faults. They appear as scars on the outermost layer of Earth. A lot is going on along the largest of faults: mountains can grow, volcanoes can erupt, continents can separate and earthquakes happen.Also more discrete events are constantly happening close to faults: The emission of the greenhouse gas methane from ocean floor commonly occurs in gas hydrate provinces along tectonically active continental margins.Active methane seepage happening frequently This is what makes brittle faults particularly alluring for CAGE/NGU researcher Jochen Knies. He is one of the coauthors of a new study in Nature Communications that, for the first time, precisely dates the evolution of a brittle fault from its initial formation to its later reactivation.Brittle faults may be important because they open up pathways along which methane, released from the reservoirs deep under Earth's crust, can migrate to shallower depths or even into the ocean itself."Active methane leakage from the sea floor happens episodically, and frequently. Some seeps activate annually, others become active on a millennial scale. We need to better identify and characterize timing and duration of these leaks. It is critical for our understanding of the role the natural gas emissions play on global climate." says Jochen Knies, researcher at CAGE/NGU.The story of the faults is the story of methane release Methane is a very potent greenhouse gas. The impacts of the industrial and agricultural release of the gas are well known and mapped. But the effects and quantities of the natural release of the gas, especially from the ocean floor, are poorly understood. Recent studies show that this natural release has been heavily underestimated.The Nature Communications study focuses on brittle faults and fractures onshore in western Norway. Up to now, applications for directly fingerprinting the age of brittle faulting and reactivation -- and thus potentially the timing of gas emission through the crust -- did not exist."We have managed to precisely date several episodes of faulting and reactivation of brittle faults onshore Norway. Our study unravels and dates a complex evolution of the local brittle deformation, which straddles a 200 million year timespan." says Giulio Viola, the lead-author of the study .The onshore study gives scientists the necessary tools to understand the age of offshore faults, which are important for methane release from gas hydrate provinces.Improving the models and estimates of methane release The innovative method behind the study combines a twofold approach: the detailed structural analysis of faults, and the dating of their history by applying potassium/argon dating of the clay mineral illite. The faulting causes deformations in which illite can form, and just a few milligrams of the clay mineral are enough to do this type of dating."Testing this toolbox on fault and fracture systems below active sites of methane leakages, would potentially provide an innovative and unique possibility: By constraining the timing of offshore faulting episodes, we may ultimately be able to identify the events of increased methane emission to the ocean and atmosphere. These episodes are not something that is restricted to the past. They are happening now, and will be happening frequently in the future," concludes Knies.The method and the findings may also improve current models that estimate the amounts of methane released from natural sources. | Earthquakes | 2,016 |
November 29, 2016 | https://www.sciencedaily.com/releases/2016/11/161129152509.htm | Groundwater helium level could signal potential risk of earthquake | Japanese researchers have revealed a relationship between helium levels in groundwater and the amount of stress exerted on inner rock layers of Earth, found at locations near the epicenter of the 2016 Kumamoto earthquake. Scientists hope the finding will lead to the development of a monitoring system that catches stress changes that could foreshadow a big earthquake. | Several studies, including some on the massive earthquake in Kobe, Japan, in 1995, have indicated that changes to the chemical makeup of groundwater may occur prior to earthquakes. However, researchers still needed to accumulate evidence to link the occurrence of earthquakes to such chemical changes before establishing a strong correlation between the two.A team of researchers at the University of Tokyo and their collaborators found that when stress exerted on Earth's crust was high, the levels of a helium isotope, helium-4, released in the groundwater was also high at sites near the epicenter of the 2016 Kumamoto earthquake, a magnitude 7.3 quake in southwestern Japan, which caused 50 fatalities and serious damage.The team used a submersible pump in deep wells to obtain groundwater samples at depths of 280 to 1,300 meters from seven locations in the fault zones surrounding the epicenter 11 days after the earthquake in April 2016. They compared the changes of helium-4 levels from chemical analyses of these samples with those from identical analyses performed in 2010."After careful analysis and calculations, we concluded that the levels of helium-4 had increased in samples that were collected near the epicenter due to the gas released by the rock fractures," says lead author Yuji Sano, a professor at the University of Tokyo's Atmosphere Ocean Research Institute.Furthermore, scientists estimated the amount of helium released by the rocks through rock fracture experiments in the laboratory using rock samples that were collected from around the earthquake region. They also calculated the amount of strain exerted at the sites for groundwater sample collection using satellite data. Combined, the researchers found a positive correlation between helium amounts in groundwater and the stress exertion, in which helium content was higher in areas near the epicenter, while concentrations fell further away from the most intense seismic activity."More studies should be conducted to verify our correlation in other earthquake areas," says Sano. "It is important to make on-site observations in studying earthquakes and other natural phenomena, as this approach provided us with invaluable insight in investigating the Kumamoto earthquake," he adds. | Earthquakes | 2,016 |
November 28, 2016 | https://www.sciencedaily.com/releases/2016/11/161128151243.htm | What's up with Madagascar? | Madagascar, the big island off the east coast of Africa with the lemurs and baobabs, is thought to be sitting in the middle of an old tectonic plate, and so, by the rules of plate tectonics, should be tectonically quiet: few earthquakes and no volcanoes. | But it's not. The island has been away from tectonic action for the past 80 million years, said Martin Pratt, research scientist in earth and planetary sciences at Washington University in St. Louis, yet it experiences about 500 earthquakes per year.The island also has volcanoes that have been active within the recent geologic past. "Having active volcanoes in Madagascar is like having erupting volcanoes in St. Louis," said Michael Wysession, professor of earth and planetary sciences. "You have to ask yourself, 'What are they doing there?'"Since this part of the world is geologically complex, there are lots of interesting possible explanations for the volcanoes. To figure it out, the geologists needed to be able to examine not just the island's accessible surface, but also what lies beneath the rigid crust and upper mantle.To image Earth's interior, geologists use a technique called seismic tomography that is similar to the medical CT scan, probing Earth's strictire with seismic waves from distant earthquakes and ambient noise. But remote and politically unstable Madagascar was largely unexplored by seismic methods until recently.Starting in 2010, however, three groups, including one led by Washington University seismologists Wysession and Doug Wiens, began to deploy seismic arrays on Madagascar, on nearby islands in the Mozambique channel (between the island and Africa), and on the ocean floor east of Madagascar.In an article published online Nov. 22 in Earth and Planetary Science Letters, the Washington University scientists report that they found three areas of hot rock within the mantle beneath three separate volcanic provinces on the island.They also see signs that the bottom of the lithosphere beneath the central volcanic province has peeled off. As the cold rock sank into the mantle, hotter rock flowed around it to the center and the south of the island. The crust, unburdened, bobbed higher. The northern volcanic province, meanwhile, probably taps a different heat source.A busted-up chunk of an ancient continentMadagascar, originally part of the ancient continent Gondwana, was formed in two steps. The island, together with India, pulled away from Africa 150 million years ago, stretching and thinning the crust on the island's west coast before it finally snapped off. The thinned crust on the west coast sagged and the dips filled with sediments, forming deep basins of sedimentary rocks.Then, about 90 million years ago, when the mini-continent migrated over the Marion hotspot (a mantle plume that now lies beneath the Antarctic plate to the south), brief but voluminous eruptions covered the island in lava. The blast of heat is thought to have cracked the overriding continent into two parts, Madagascar and India, which scraped past the east coast of Madagascar on its way north toward Asia, leaving a very straight coastline there.But the volcanism in the central, northern, and southern provinces are much younger than the basaltic remains of the 90-million-year-old eruption still found around the perimeter of Madagascar. So the question was: Where did they come from?What the images showLead-author Pratt used three complementary methods to analyze surface waves (seismic waves trapped near Earth's surface), which are created by distant earthquakes and from sources of seismic noise, such as ocean storms."His approach is clever and creative," Wysession said. "He's taken three really different data sets, some good at high frequencies that give you better resolution at shallow depths, and some better at low frequencies that give you better resolution at greater depths, and he's put them all together. It's a bit like combining an X-ray, an MRI and a CT scan to get a clearer image."The images show three low-velocity seismic anomalies corresponding to the upwelling of hotter mantle rock along the island's backbone."We knew about the named volcanic provinces in the center and north," Wysession said. "But we didn't know about the one in the southwest. When we saw the third blob in the images, we checked the literature and discovered that, sure enough, there was volcanic activity there as recently as 9 million years ago."The cause of the three hot regions in the mantle is a mystery, however. Though there is some indication from the tomographic images that the regions might be connected, particularly the southern two, further modeling of deeper structure will be needed to confirm.One origin of the hot regions previously has been proposed to be hot rock rising through the mantle as the Comores hot spot, which has created a set of volcanic islands just west of the north end of the island.The authors have a different idea, however, and it comes from the way that the central and southwestern provinces appear to be connected at depth."If you look at the images that Martin has made," Wysession said, "you can see a horseshoe shape where the central hot mantle anomaly swings west and then comes back east again, connecting the central and southern provinces.The deflecting obstacle seems to be a slab of colder rock. "We think the lithosphere (the crust and rigid upper mantle) has delaminated, and the bottom of it fell off," Wysession said. "As the cold, dense slab began to sink, hotter rock flowed up and in to replace it, buoying the central province and, as it tilted, blocking flow to the south."But what caused the bottom of the lithosphere to peel off? "We think it may have been the Marion hotspot," Wysession said. "The underside of the plate was heated by this huge blow torch 95 million years ago, weakening the rock enough that it was able to peel off. So we're still seeing collateral damage from this ancient event."This idea also has the advantage of explaining the unusually high elevations of the northern half of the island. Once the heavy bottom of the plate fell off, it stopped pulling down the crust, which rebounded upward as much as a kilometer as hot rock from below took the place of the delaminated slab.Something similar happened underneath the Great Basin of the western United States, he said, where the bottom of the lithosphere also split off, forming a large blob of cold material sinking down through the mantle below the surface of central Nevada. There, the blow torch that delaminated the plate was an ocean spreading center that was overridden by the North American plate, Wysession said. | Earthquakes | 2,016 |
November 28, 2016 | https://www.sciencedaily.com/releases/2016/11/161128132928.htm | Biggest exposed fault on Earth discovered | Geologists have for the first time seen and documented the Banda Detachment fault in eastern Indonesia and worked out how it formed. | Lead researcher Dr Jonathan Pownall from The Australian National University (ANU) said the find will help researchers assess dangers of future tsunamis in the area, which is part of the Ring of Fire -- an area around the Pacific Ocean basin known for earthquakes and volcanic eruptions."The abyss has been known for 90 years but until now no one has been able to explain how it got so deep," Dr Pownall said."Our research found that a 7 km-deep abyss beneath the Banda Sea off eastern Indonesia was formed by extension along what might be Earth's largest-identified exposed fault plane."By analysing high-resolution maps of the Banda Sea floor, geologists from ANU and Royal Holloway University of London found the rocks flooring the seas are cut by hundreds of straight parallel scars.These wounds show that a piece of crust bigger than Belgium or Tasmania must have been ripped apart by 120 km of extension along a low-angle crack, or detachment fault, to form the present-day ocean-floor depression.Dr Pownall said this fault, the Banda Detachment, represents a rip in the ocean floor exposed over 60,000 square kilometres."The discovery will help explain how one of Earth's deepest sea areas became so deep," he said.Professor Gordon Lister also from the ANU Research School of Earth Sciences said this was the first time the fault has been seen and documented by researchers."We had made a good argument for the existence of this fault we named the Banda Detachment based on the bathymetry data and on knowledge of the regional geology," said Professor Lister.Dr Pownall said he was on a boat journey in eastern Indonesia in July when he noticed the prominent landforms consistent with surface extensions of the fault line."I was stunned to see the hypothesised fault plane, this time not on a computer screen, but poking above the waves," said Dr Pownall.He said rocks immediately below the fault include those brought up from the mantle."This demonstrates the extreme amount of extension that must have taken place as the oceanic crust was thinned, in some places to zero," he said.Dr Pownall also said the discovery of the Banda Detachment fault would help assesses dangers of future tsunamis and earthquakes."In a region of extreme tsunami risk, knowledge of major faults such as the Banda Detachment, which could make big earthquakes when they slip, is fundamental to being able to properly assess tectonic hazards," he said. | Earthquakes | 2,016 |
November 24, 2016 | https://www.sciencedaily.com/releases/2016/11/161124151450.htm | Fault curvature may control where big earthquakes occur | Major earthquakes -- magnitude 8.5 and stronger -- occur where faults are mostly flat, say University of Oregon and French geologists. Curvier faults, they report in the journal | Large earthquakes, known as mega-quakes, were long thought to be possible only at the boundary between fast converging, young tectonic plates until two giant earthquakes -- the magnitude 9.4 quake in Indonesia in 2004 and the 9.0 quake in Japan in 2011 -- disconfirmed the theory.Since then giant earthquakes have been thought to be possible on any large fault. In the new paper UO researchers show that the maximum size of earthquakes may be controlled by another parameter: the fault curvature."The way people in the science community think about earthquakes is that some fault areas resist failure more than others, and when they break they generate large earthquakes," said lead author Quentin Bletery, a postdoctoral researcher at the UO. "The reason they resist failure longer is often debated. I thought variations in fault geometry could be responsible, so I looked for changes in the slope of the major subduction faults of the world."Bletery had arrived at the UO with the idea that geometry could provide clues, based on his doctoral work at the Universite Nice -- Sophia Antipolis. He developed a mechanical model to study his theory in collaboration with UO co-authors Amanda Thomas, Alan Rempel and Leif Karlstrom, all in the Department of Earth Sciences.For the National Science Foundation-supported research, Bletery examined the geometry of subduction faults around the world to find the slope gradients, not the steepness of dipping itself, but its variations."I calculated the gradient of the slope (or curvature) curvature along the main faults and compared it with the distribution of very large earthquakes that happened in the past," he said. "What I found is the opposite of what I expected: Very large earthquakes occur on fault areas where the slope is the most regular, or flat."The Cascadia fault, which last experienced a mega-quake in 1700, lies along such a flat region, Rempel and Thomas said."Earthquakes like the one that happened in Sumatra are mind-bogglingly large," Thomas said. "The rupture was 1,600 kilometers (994 miles) long. When Cascadia goes, it could be 1,000 kilometers (621 miles) if it ruptures completely."A key aspect is that rupture thresholds are more heterogeneous along curved faults, therefore ruptures distances are restricted by portions of curvy sections that are not ready to fail. The rupture threshold is more homogeneous along flat faults, allowing larger fault areas to rupture simultaneously, the researchers said."The correlation of the curvatures to mega-quakes is strong," Thomas said. "The data don't lie."Based on the average curvature inside the giant earthquake rupture areas, the researchers concluded that the likelihood that mega-earthquakes are linked to fault curvatures is more than 99 percent.The discovery is not expected to have direct impact on the ability of scientists to predict when an earthquake will occur, Thomas said."Instead, our findings backstop the idea that if you are at a location that hasn't had evidence for large earthquakes in the past and your location is on a curvy plate, then maybe mega-quake will never happen," Rempel said. "Not all subduction zones can have really large earthquakes is the implication of this study."That's not to say a 7.5 quake can't cause significant damage, Thomas said. "The next step in the research is asking why having a flat plate is more amenable to a large earthquake than a curvy plate," she said. The information eventually, she said, could lead to improved hazard maps for earthquake-prone areas around the world. | Earthquakes | 2,016 |
November 24, 2016 | https://www.sciencedaily.com/releases/2016/11/161124150207.htm | Subduction zone geometry: Mega-earthquake risk indicator | Mega-earthquakes (with a magnitude greater than 8.5) mainly occur on subduction faults where one tectonic plate passes under another. But the probability of such earthquakes does not appear to be even across these zones. In a study published on 25 November 2016 in the journal | At the point where two tectonic plates converge, an area known as the subduction zone can form where one of the plates passes on top of the other. Rocks do not slide over one another easily and the movement of tectonic plates can be blocked along the entire length of such interaction zones for periods exceeding a thousand years. This 'slip deficit' results in an accumulation of energy, which is released abruptly during earthquakes.A theory that held sway for many years suggested that mega-earthquakes mostly occurred in subduction zones where plates converged rapidly and those where the subducting plate was relatively young. However, the mega-earthquakes of Sumatra-Andaman in 2004 and Tohoku-Oki in 2011, which generated deadly tsunamis, go against this theory: in the first case, the speed of plate movement is relatively slow (3 to 4 cm per year) and in the second, the Pacific plate that subducts under Japan is more than 120 million years old. A new question therefore arose: can all subduction zones generate mega-earthquakes?In this new study, the researchers examined another parameter: subduction zone geometry. By comparing the degree of curvature of the subducting plates in great historical earthquakes, they discovered that the maximum magnitude of earthquakes recorded in each subduction zone was inversely proportional to the degree of curvature of the fault. In other words, the flatter the contact between the two plates, the more likely it is that mega-earthquakes will occur.Earthquakes take place once the energy accumulated as a result of the slip deficit exceeds a certain threshold. The researchers showed that the greater the curvature of the subduction fault, the more this threshold varies along the subduction zone. A heterogeneous threshold produces more frequent earthquakes, but these affect a smaller spatial area and are therefore of lower magnitude. In contrast, a homogeneous rupture threshold over a large portion of a fault has a greater chance of resulting in a simultaneous rupture of the whole blocked zone and, consequently, a greater chance of generating a mega-earthquake.As a consequence, subduction zones such as the Philippines, Salomon Islands or Vanuatu do not appear likely to generate mega-earthquakes. Others, however, such as Peru, Java or Mexico, which have not seen very large earthquakes over the last 200-300 years, appear to have all the necessary characteristics for a mega-earthquake in the future. | Earthquakes | 2,016 |
November 21, 2016 | https://www.sciencedaily.com/releases/2016/11/161121161559.htm | Scientists reconstruct formation of the southern Appalachians | Around 300 million years ago, the landmass that is now North America collided with Gondwana, a supercontinent comprised of present-day Africa and South America. That clash of continents lifted tons of rock high above the surrounding terrain to form the southern end of the Appalachian Mountains now seen in Alabama, Tennessee and Georgia. A team of geophysicists has reconstructed the terminal phase of that collision and developed a new picture of how it unfolded. | The study, led by Brown University researchers, used seismic monitoring stations to create a sonogram-like image of the crust beneath the southern U.S., near of the southern base of the Appalachians. The research shows that Gondwana crust was thrust atop North America when the two continents collided, sliding northward as much as 300 kilometers before the two continents separated and drifted apart about 200 million years ago. The process revealed by the study looks a lot like the process that is building the Himalayas today, as the Eurasian continent is pushing atop the Indian subcontinent."We show that a continental collision that occurred 300 million years ago looks a lot like the collision we see in the Himalayas today," said Karen Fischer, a professor in Brown's Department of Earth, Environmental and Planetary Sciences and a co-author of the study. "This is the best-documented case I'm aware of in which the final suture between ancient continental crusts has a geometry similar to the present-day India-Eurasia crustal contact beneath the Himalayas."The research was led by Emily Hopper, who earned her doctorate from Brown in 2016 and is now a postdoctoral fellow at the Lamont-Doherty Earth Observatory of Columbia University. The study is published online in the journal For the study, the research team placed 85 seismic monitoring stations across southern Georgia and parts of Florida, North Carolina and Tennessee. The researchers also used data from the Earthscope Transportable Array, a rolling array of seismic stations that made its way across the contiguous U.S. between 2005 and 2015. In all, 374 seismic stations recorded the faint vibrational waves from distant earthquakes as they traveled through the rocks beneath.Acoustic energy from earthquakes can travel though Earth as different types of waves, including shear waves, which oscillate perpendicular to the direction of propagation, and compressional waves, which oscillate in the same direction as they propagate. By analyzing the extent to which shear waves convert to compression waves when they hit a contrast in rock properties, the researchers could create a seismic image of the subsurface crust.The study detected a thin continuous layer of rock that starts near the surface and slopes gently to the south to depths of approximately 20 kilometers, in which earthquake waves travel faster than in the surrounding rocks. That layer stretches southward about 300 kilometers from central Georgia to northern Florida. It spans about 360 kilometers east to west, from the central part of South Carolina, across all of Georgia and into eastern Alabama.The mostly likely explanation for that anomalous layer, the researchers say, is that it's a shear zone -- the contact along which Gondwanan plate slid atop of the proto-North American plate."Where these two crustal blocks came into contact, there would have been tremendous deformation that aligned the mineral grains in the rocks and changed the propagation velocities of the seismic waves," Fischer said. "So our preferred explanation for this continuous layer is that we're seeing mineral alignment on the shear zone between these two plates."The presence of this widespread, gently sloped shear zone paints a new picture of the final stages of the collision between the two continents. Researchers had long thought that proto-North American and Gondwana collided on a shear zone with a much steeper slope, leading some to the view that the two plates slid laterally past each other. But such a steep shear zone would be in stark contrast to the 300 kilometers of nearly horizontal shear zone found in this new study.The geometry of the contact detected in the study is similar to the process that is currently raising the Himalayas. In that collision, Fischer says, Eurasian crust has overtopped the Indian subcontinent by a distance similar to that found in the Appalachians. That process continues today, raising the Himalayas by 4 to 10 millimeters per year.The similarity between the two events tells scientists that there's consistency over time in the way mountains are built, Fischer says."When we think of mountain-building, the Himalayas are the archetype," she said. "It's interesting that a collision that took place 300 million years ago is very similar to one happening today."And that has implications for understanding the way Earth's crust has evolved."What that tells us is that the way the crust deforms -- where it's weak, where it's strong and how it accommodates deformation -- has been fairly uniform through time," Fischer said. "The crust couldn't have been much hotter; it couldn't have been much colder; and it couldn't have had a very different distribution of fluids, as all of these things influence the way the crust deforms." | Earthquakes | 2,016 |
November 14, 2016 | https://www.sciencedaily.com/releases/2016/11/161114143656.htm | Rip in crust drives undersea volcanism | Scientists analyzing a volcanic eruption at a mid-ocean ridge under the Pacific have come up with a somewhat contrarian explanation for what initiated it. Many scientists say undersea volcanism is triggered mainly by upwelling magma that reaches a critical pressure and forces its way up. The new study says the dominant force, at least in this case, was the seafloor itself -- basically that it ripped itself open, allowing the lava to spill out. The eruption took place on the East Pacific Rise, some 700 miles off Mexico. | "Mid-ocean ridges are commonly viewed as seafloor volcanoes, operating like volcanoes on land," said the study's lead author, Yen Joe Tan, a graduate student at Columbia University's Lamont-Doherty Earth Observatory. "We're saying they should actually be viewed as tears in the crust, where magma oozes out." The study appears in the journal The mid-ocean ridges are mountain chains that run continuously for more than 40,000 miles along the planet's seafloors, like stitching on a baseball. From their centers, they pour out lava. This pushes the seafloor out in opposite directions from the ridges toward the continents. In many cases, the leading edge of the seafloor then dives under the land, or subducts, and is subsumed back into the deep earth. This process -- the basic mechanism of plate tectonics -- was defined in the 1960s and 1970s. Scientists have since debated exactly what drives ridge eruptions.Many say magma pressure is the main factor, but it might not be the only one. A ridge might also get torn by what specialists call "plate pull" -- the force exerted when the distant edge of seafloor subducts under a continent, slowly lugging the rest behind it. Stress might also develop because eruptions build symmetrical chains of mountains on either side of the ridge axis, as lava spills down the sides. This might weaken the center through sheer force of gravity, somewhat like what happens when one slices a hot dog lengthwise, and the two sides fall apart.In an effort to resolve the relative roles of magma and stress, Tan and his coauthors analyzed an eruption thought to have taken place in 2005-2006, along a heavily studied segment of the East Pacific Rise. A team of researchers had earlier left underwater microphones and sea-bottom seismometers at the site, which recorded the eruption. They later retrieved the sound and seismic data, and mapped the fresh lava using underwater cameras. They also collected samples of the lava, and later analyses of it suggested that the eruption took place over seven to 10 months.The authors of the new paper took another look after a 2015 eruption at an unconnected study site, at Axial Seamount, off the coast of Oregon. Unlike the earlier East Pacific Rise eruption, this one was studied in real time with an assortment of instruments. Among the data produced were recordings of violent popping noises that appeared related to the emergence of lava on the seafloor -- possibly the result of exploding gas bubbles, or implosions of hardening lava.In light of the Axial Seamount observations, the researchers reviewed the 2005-2006 data from the East Pacific Rise, and came up with a newly sharpened picture. Their reanalysis suggested that most of the eruption took place rapidly, not over months. Other researchers had already identified a series of conventional earthquakes of about magnitude 2 on Jan. 22, 2006, of the kind usually associated with the rupture of a rock boundary, along a 35-kilometer-long segment of the ridge. About 15 minutes later, the seismometers started picking up clusters of lower-frequency earthquakes, of a type usually associated with rising magma. Another hour or two on, popping sounds like those heard at Axial Seamount appeared, in four separate areas along the segment, each in an area about 5 kilometers long.The team pinned down the locations of the sounds, and when they overlaid these with the earlier map of the fresh lava, they matched. Their interpretation: the first series of earthquakes signaled the rupture of a fault overlying the magma, with little or no help from magma pressure. Then, with a path now clear, the magma ascended. Magma pressure was probably not the initial trigger for the eruptions, say the authors, because they came simultaneously from four separate places along the apparent ruptured fault."It's been a kind of chicken-and-egg question," said coauthor Maya Tolstoy, a marine geophysicist at Lamont-Doherty. "You have these two different forces [magma vs. tectonics] that could play a role, and it's hard to tell which triggers the eruption. Here, we can make the argument for one dominating, because we see this series of events, and then multiple magma chambers erupting at the same time."The authors say that according to their observations, about 85 percent of the lava emerged within two days, with remnants dribbling out over the course of a week. The eruptions produced some 22 million cubic meters of seafloor -- about enough to cover 13 football fields 1,000 feet deep.Cynthia Ebinger, a professor at the University of Rochester who studies eruptions at spreading sites both on land and under the ocean, said in an email that very few seafloor eruptions have been so directly observed. The study "adds a new factor to consider," she said. "It shows that tectonic stresses can trigger large-volume intrusions and eruptions" to create new seafloor.Michael Perfit, a professor at the University of Florida who also studies undersea eruptions, said the study "tells a remarkable story." But, he said, the authors may have overstated the relative role of tectonic stress versus magma pressure. "I think it's really got to be both," he said. He cited a 2014 geochemical study he coauthored suggesting that the magma was replenished with new material from below about 6 weeks before the eruption. This suggests pressure could have played a more substantial role, he said.Ebinger said it remained possible that either magma pressure or tectonic forces could be "the straw that breaks the camel's back" in any specific eruption.The paper was also coauthored by seismologist Felix Waldhauser of Lamont-Doherty and marine geophysicist William Wilcock of the University of Washington. The research was supported by the U.S. National Science Foundation. | Earthquakes | 2,016 |
November 14, 2016 | https://www.sciencedaily.com/releases/2016/11/161114124949.htm | Geologists discover how a tectonic plate sank | In a paper published in | John Encarnacion, Ph.D., professor of earth and atmospheric sciences at SLU, and Timothy Keenan, a graduate student, are experts in tectonics and hard rock geology, and use geochemistry and geochronology coupled with field observations to study tectonic plate movement."A plate, by definition, has a rigidity to it. It is stiff and behaves as a unit. We are on the North American Plate and so we're moving roughly westward together about an inch a year," Encarnacion said. "But when I think about what causes most plates to move, I think about a wet towel in a pool. Most plates are moving because they are sinking into Earth like a towel laid down on a pool will start to sink dragging the rest of the towel down into the water."Plates move, on average, an inch or two a year. The fastest plate moves at about four inches a year and the slowest isn't moving much at all. Plate motions are the main cause of earthquakes, and seismologists and geologists study the details of plate motions to make more accurate predictions of their likelihood."Whenever scientists can show how something that is unexpected might have actually happened, it helps to paint a more accurate picture of how Earth behaves," Encarnacion said. "And a more accurate picture of large-scale Earth processes can help us better understand earthquakes and volcanoes, as well as the origin and locations of mineral deposits, many of which are the effects and products of large-scale plate motions."Plate movement affects our lives in other ways, too: It recently was reported that Australia needs to redraw its maps due to plate motion. Australia is moving relatively quickly northwards, and so over many decades it has traveled several feet, causing GPS locations to be significantly misaligned.Subduction, the process by which tectonic plates sink into Earth's mantle, is a fundamental tectonic process on earth, and yet the question of where and how new subduction zones form remains a matter of debate. Subduction is the main reason tectonic plates move.The SLU geologists' research takes them out into the field to study rocks and sample them before taking them back to the lab to be studied in more detail.Their work involves geological mapping: looking at rocks, identifying them, plotting them on a map and figuring out how they formed and what has happened to them after they form. Researchers date rock samples and look at their chemistry to learn about the specific conditions where an ancient rock formed, such as if a volcanic rock formed in a volcanic island like Hawaii or on the deep ocean floor.In this study, Keenan and Encarnacion traveled to the Philippines to study plates in that region. They found that a divergent plate boundary, where two plates move apart, was forcefully and rapidly turned into a convergent boundary where one plate eventually began subducting.This is surprising because although the plate material at a divergent boundary is weak, it is also buoyant and resists subduction. The research findings suggest that buoyant but weak plate material at a divergent boundary can be forced to converge until eventually older and denser plate material enters the nascent subduction zone, which then becomes self-sustaining."We think that the subduction zone we studied was actually forced to start because of the collision of India with Asia. India was once separated from Asia, but it slowly drifted northwards eventually colliding with Asia. The collision pushed out large chunks of Asia to the southeast. That push, we think, pushed all the way out into the ocean and triggered the start of a new subduction zone."Their finding supports a new model for how plates can begin to sink: "Places where plates move apart can be pushed together to start subduction."The SLU researchers now want to learn if their model applies to other tectonic plates."How common was this forced initiation of a subduction zone that we think happened in the Philippines?" Encarnacion said. "I would like to see work on other ancient subduction zones to see whether our model applies to them as well."Other researchers on the study include Robert Buchwaldt, Dan Fernandez, James Mattinson, Christine Rasoazanamparany, and P. Benjamin Luetkemeyer.Saint Louis University's Department of Earth and Atmospheric Sciences, combines strong classroom and field-based instruction with internationally recognized research across a broad spectrum of the physical sciences, including seismology, hydrology, geochemistry, meteorology, environmental science, and the study of modern and ancient climate change. Students also have the opportunity to work directly with faculty on their research and pursue internships through a growing network of contacts in the public and private sector.Research centers include the Earthquake Center, the Cooperative Institute for Precipitation Systems, the Global Geodynamics Program, the Center for Environmental Sciences, and Quantum WeatherTM. The fusion of academic programs with world-class research provides students with an unparalleled opportunity to explore their interests and prepare for a wide variety of careers after graduation. | Earthquakes | 2,016 |
November 11, 2016 | https://www.sciencedaily.com/releases/2016/11/161111133314.htm | Safest locations for wastewater injection | Stanford geophysicists have compiled the most detailed maps yet of the geologic forces controlling the locations, types and magnitudes of earthquakes in Texas and Oklahoma. | These new "stress maps," published in the journals "These maps help explain why injection-induced earthquakes have occurred in some areas, and provide a basis for making quantitative predictions about the potential for seismic activity resulting from fluid injection," said study co-author Mark Zoback, the Benjamin M. Page Professor of Geophysics in Stanford's School of Earth, Energy & Environmental Sciences.To create these stress maps, Zoback and his graduate students Jens-Erik Lund Snee and Richard Alt interpreted data from different parts of Texas and Oklahoma donated by oil and gas companies. "Companies routinely collect data that can be used for assessing the state of stress in Earth as part of their normal oil and gas operations," Lund Snee said.When combined with information about the faults present in a given area, the scientists were able to assess which faults are likely to be problematic and why. In the areas where induced earthquakes have occurred in Texas and Oklahoma, the Stanford scientists show that a relatively small increase of pore pressure -- the pressure of fluids within the fractures and cavities of rocks -- would have been sufficient to trigger slip.In a related paper published recently in the journal The Stanford scientists also found that many of the recent earthquakes in Texas that have been suspected as being triggered by wastewater injection occurred on faults that -- according to the new map -- have orientations that are nearly ideal for producing earthquakes. Hence, doing this kind of study in advance of planned injection activities could be very helpful."By identifying which faults are potentially active in advance, companies and regulators can avoid problematic faults during fluid injection and prevent the induced earthquakes from happening before they do," Zoback said. | Earthquakes | 2,016 |
November 9, 2016 | https://www.sciencedaily.com/releases/2016/11/161109132623.htm | Key indicator of carbon sources in Earth's mantle | Scientists have found a key indicator in determining whether the presence of carbon, found in the Earth's mantle, is derived from continental crust -- a step toward better understanding the history of crustal formation on Earth's surface and the rate at which tectonic plates have moved throughout geologic time, which can be linked to the cooling of Earth's mantle. | Results of a new study published in the journal Three theories exist regarding the source of carbon found within the Earth's mantle: It is of primordial origin, formed during the creation of the planet 4.56 billion years ago; it is a result of planetary collision; or it had been present in marine environments or continental crust, and recycled back into the mantle in areas of subduction, where tectonic plates shifted, one diving beneath the other."Our most important finding is that the Boron isotope ratios are highly variable, indicating that the source of carbon within the mantle changed with geological time on Earth," Simonetti said. Studying the ratios of boron isotopes within carbonatites, researchers are closer to determining which hypothesis applies to specific moments in geological time."During the past 4.56 billion years, the subduction rate has varied," said Simonetti. "Early on, during the first 2 billion years or so, Earth's mantle was much hotter than it is today, so when subduction did occur, the diving plate did not penetrate as deep into the mantle as it does today because of the higher temperature. During the last 2 billion years or so, a cooler mantle has allowed the subducting plate to dive deeper into the mantle and provide the opportunity to store recycled crustal materials at greater depths, and possibly all the way down to the core-mantle boundary."This preliminary investigation into the boron isotope compositions of carbonatites from significant periods in Earth's history allows Simonetti and his team to monitor long-term temporal variations -- creating a clearer picture of crustal formation over time, with the potential to go as far back as several billion years.The study was co-authored by Samuel R.W. Hulett in the Department of Civil and Environmental Engineering and Earth Sciences at Notre Dame, E. Troy Rasbury of Stony Brook University N. Gary Hemming of Queens College -- CUNY. | Earthquakes | 2,016 |
November 1, 2016 | https://www.sciencedaily.com/releases/2016/11/161101100233.htm | Some Los Angeles earthquakes possibly triggered by oil production in early 20th century | Historical sleuthing has turned up evidence for a possible link between oil production and a handful of damaging earthquakes that took place in the Los Angeles Basin during its oil boom in the early 20 | In particular, the 1920 Inglewood quake, the 1929 Whittier quake, the 1930 Santa Monica quake and the 1933 Long Beach earthquake may have been induced by oil production activities that took place prior to the time of the seismic events, say Susan Hough and Morgan Page of the U.S. Geological Survey.Their study is one of the first to look at evidence for earthquakes caused by industry activity in the Los Angeles region before 1935. Oil and gas production practices then were significantly different from today's retrieval methods, the researchers note, so their findings "do not necessarily imply a high likelihood of induced earthquakes at the present time" in the L.A. Basin.Other studies have concluded that there was no significant evidence for induced earthquakes in the area after 1935."With the advent of water flooding and other changes in industry practices, you may not find these kinds of induced earthquakes after 1935," says Hough. "It's possible it was just an early 20If researchers can confirm that some of these larger earthquakes such as the magnitude 6.4 Long Beach quake were human-caused, however, the findings could re-shape how seismologists calculate the rate of natural earthquake activity in the basin."If you take our four-the 1920, 1929, 1930 and 1933 earthquakes-out of the calculations as induced or potentially induced, it does call into question what the rate of natural earthquakes in the L.A. Basin really is," Hough suggests. "Maybe the L.A. Basin as a geological unit is more seismically stable than we've estimated."Los Angeles' oil boom began in 1892 when oil was discovered near present-day Dodger Stadium, and L.A. Basin oil fields accounted for nearly 20 percent of the world's total production of crude oil by 1923. Despite this massive scale of production, it does not appear that induced earthquakes were common in the basin during the early 20Compiling the data to study this question, however, was a complicated task for Hough and Page. The researchers had to put together a list of all "felt" earthquake events in the L.A. Basin during the time period, using reports of shaking and property damage to calculate quake epicenters and magnitudes for earthquakes recorded by few if any seismometers.For Hough, this meant a few interesting trips through the Cal Tech archives, where she found historical gems such as renowned seismologist Charles Richter's unpublished notes on the 1929 Whittier earthquake. "I was literally following in his footsteps, for example where he had gone down San Gabriel Boulevard, starting in Pasadena, and stopping at every place where there was a dwelling and making observations of earthquake effects," she says.Hough's earlier studies of historic induced earthquakes in Oklahoma gave her the idea to look for oil permits and other industry records online, and she eventually found a site containing state reports that summarized the operations of California oil fields in the early 20By comparing the earthquake lists with the industry data, the researchers found several links between earthquakes and significant oil production activities that took place nearby and close to the same time as the quakes. The precise location of the wells-whether they were close to a existing fault, for instance-along with well depth, appear to be important factors in whether an earthquake was induced.Drilling deeper "gets you closer to the basement rock, and that is where the tectonically active faults are, the ones that are storing up tectonic stress," Hough explains.The recent increase in human-caused earthquakes in the central United States and Canada make it important to understand the "full context" of how, where and why earthquakes are induced, Hough notes. "We want to look at all the data we can, because the last decade is a just a tiny snapshot of the record that we have for induced seismicity." | Earthquakes | 2,016 |
October 26, 2016 | https://www.sciencedaily.com/releases/2016/10/161026104844.htm | Entire Himalayan arc can produce large earthquakes | The main fault at the foot of the Himalayan mountains can likely generate destructive, major earthquakes along its entire 2,400-kilometer (1,500-mile) length, a new study finds. Combining historical documents with new geologic data, the study shows the previously unstudied portion of the fault in the country Bhutan is capable of producing a large earthquake and did so in 1714. | "We are able for the first time to say, yes, Bhutan is really seismogenic, and not a quiet place in the Himalayas," said György Hetényi, a geophysicist at the University of Lausanne, Switzerland and lead author of the new study accepted for publication in The Himalayas have produced some of the world's largest earthquakes, like the April 2015 Gorkha earthquake that devastated Nepal. But scientists had not been able to prove whether every region along the 2,400-kilometer arc was seismogenic, or capable of producing quakes. Bhutan was one of the last open gaps along the mountain chain: the country had no records of recent major earthquakes and no major seismological work had been done there.Confining a major earthquake to Bhutan in 1714, like the new study does, means the entire Himalayan arc has experienced a major earthquake in the past 500 years, according to the study's authors. By filling this gap, the new study helps the millions of residents in the region understand its potential for natural hazards, according to Hetényi."We provide a longer and therefore more representative record of seismicity in Bhutan, and this makes better hazard estimates," he said.The highest mountain range on Earth, the Himalayas are the product of the Indian tectonic plate subducting under the Eurasian Plate. The mountains span a northwest to southeast arc roughly 2,400 kilometers (1,500 miles) long, nearly the distance between the U.S. East and West coasts.Throughout the 20th century, Bhutan, a small nation east of Nepal sandwiched between India and China, had been relatively isolated from the outside world and scientists were rarely allowed inside its borders. Until recently, researchers thought Bhutan could be the only major segment of the Himalayas not to have experienced a major earthquake in the last 500 years, according to Hetényi.But, after a magnitude 6 earthquake struck the country in 2009, the government opened the door for scientists to perform geophysical research, Hetényi said.Hetényi and his colleagues made several trips to the country from 2010 to 2015 to catalog small earthquakes in the area and study how the structure of the Indian Plate changes as it subducts below the crushing belt of mountains. One question they were hoping to answer was whether Bhutan had historically experienced any major destructive earthquakes.Historical records of earthquakes in Bhutan are rare, but by luck Hetényi stumbled upon a biography of famous 18th century Buddhist monk and temple builder Tenzin Lekpai Dondup. The biography described a quake in early May of 1714 that destroyed the Gangteng monastery Dondup helped build.The biography and other historical records indicated there were many aftershocks, meaning it could have been a major quake, according to Hetényi.However, this description alone did not pinpoint where the quake occurred."When you only have very local devastation descriptions, you never know whether this devastation is due to an intermediate earthquake that occurred locally, nearby the chronicler, or whether it's the result of a bigger earthquake that occurred over greater distances," said Laurent Bollinger, a geologist at the French Alternative Energies and Atomic Energy Commission who was not involved in the new study.While in Bhutan, several of Hetényi's colleagues dug trenches around the fault line to see if one side of it had moved vertically with respect to the other side -- which would be considered evidence of a major earthquake. That study, led by Romain Le Roux-Mallouf, a geologist at the University of Montpellier, France, found evidence of rock uplift on one side of the fault had taken place between 1642 and 1836. Hetényi combined the results from that study with historical records of the 1714 earthquake to pinpoint where the 1714 quake happened and how large it was.Hetényi's analysis revealed the 1714 quake likely caused the rock uplift his colleagues observed around the fault. The earthquake likely occurred in west central Bhutan, where most of the population lives, and had a magnitude of at least 7.5 to 8.5, Hetényi said. By comparison, the April 2015 Gorkha earthquake had a magnitude of 7.8."It's a really significant event that happened 300 years ago," he said.The results suggest the 1714 quake was significant enough to unzip a large segment of the thrust -- possibly between 100 to 300 kilometers (60 to 200 miles) of the fault. The new study closes the seismic gap in the Himalayan arc and could help scientists better understand the earthquake potential in the densely populated Himalaya region, according to Hetényi. | Earthquakes | 2,016 |
October 20, 2016 | https://www.sciencedaily.com/releases/2016/10/161020144211.htm | Mt. Aso could erupt much sooner, scientists warn | Damage from the 2016 Kumamoto earthquake could hasten Mt. Aso's eruption, volcanologists warn. In a paper published on | Mt. Aso is one of the largest active volcanoes in the world. The 16 April 2016 Kumamoto earthquake, study authors say, were a rare opportunity to study how faults form in the vicinity of volcanoes. "Our survey group went to the epicenter area one day after the event and continued field work for the past half year after the earthquake," says Aiming Lin of Kyoto University, who led the study.The Kumamoto earthquake enabled the researchers to do a before-and-after comparison of fault distribution in the area. Field investigations, seismic data, and analysis of high-resolution Google earth images show that the earthquake produced new faults and surface ruptures.Some of these cut Aso caldera but terminated there."Magma is fluid so it absorbs stress. That's why the damage -- the co-seismic rupturing -- shouldn't travel any further," says Lin. "Large earthquakes often accompany or precede volcanic eruptions. The presence of magma does have an association with the distribution of active faults. But whether volcanoes affect the fault rupturing following an earthquake remained unclear due to the lack of case studies."Our findings show that propagation of ruptures from this earthquake terminated in Aso caldera because of the presence of magma beneath the Aso volcanic cluster."The newly formed co-seismic ruptures under Aso caldera are potential new channels for magma venting, thus changing the physical dynamics of Aso volcano, such as where pressure is concentrated. These then influence factors like the nucleation of interpolate earthquakes, seismicity patterns, source rupture processes, strong ground motion and recurrence behavior of fault segments. The study results, the authors wrote, could play an important role in reassessing volcanic hazard in the Aso volcano area.And Mt Aso did erupt 8th October 2016, after the research team had submitted the paper."We are surprised that Aso volcano erupted after a 36 years dormant duration, as we documented in this paper that the new faults changed the spatial and mechanical dynamics of Aso volcano," says Lin. | Earthquakes | 2,016 |
October 17, 2016 | https://www.sciencedaily.com/releases/2016/10/161017083935.htm | Earthquake series cause uplift variations at continental margins | A new mechanism may explain how great earthquakes with magnitudes larger than M7 are linked to coastal uplift in many regions worldwide. This has important implications for the seismic hazard and the tsunami risk along the shores of many countries. The mechanism is proposed by an international team of scientists led by Vasiliki Mouslopoulou of the GFZ German Research Centre for Geosciences in the journal | To test their hypothesis, the scientists investigated ancient coastlines that were preserved over time, so-called paleoshorelines, to determine the rate of uplift over past millennia. Vasiliki Mouslopoulou says: "It is not unlikely that coastlines along active subduction margins with no detectable tectonic uplift over the last 10,000 years will accommodate bigger than M7 earthquakes in the near future."Uplift is common along the coastlines of continents at subduction systems worldwide (e.g., Kamchatka, Japan, New Zealand and Papua New Guinea) with rates of vertical uplift accrued over the last 10,000 years being generally higher -- up to ten times more than for time intervals larger than 125,000 years.This rate variability is odd and requires explanation. The origins and the magnitude of these rate variations were examined by German (GFZ) and New Zealand (University of Canterbury) scientists using a global data set of 282 uplifted paleoshorelines from eight subduction margins globally (Italy, Greece, New Zealand, Japan, Papua New Guinea, Iran-Pakistan, Chile) and 2D numerical models.Paleoshorelines are a useful tool to constrain the magnitude and mechanisms of this uplift, as they are often spectacularly preserved as wave-cut platforms, benches and sea-notches, providing a geological record of the interplay between sea-level changes and rock uplift.Data analysis and modelling suggest that varying uplift rates along subduction margins are mainly a short-term phenomenon. For geologists, short term means shorter than 20,000 years. These uplift rates cannot be accounted for by plate-boundary processes, as previously thought. Instead, they reflect a propensity for natural temporal variations in uplift rates where recent (not more than 10,000 years ago) uplift has been greatest due to temporal clustering of large-magnitude (bigger than M7) earthquakes on upper-plate faults.Given the size and geographical extent of the analyzed dataset the conclusions of this work are likely to have wide applications.Asked what's new with these findings Vasiliki Mouslopoulou explains: "For the first time temporal clustering of great-earthquakes is shown on active subduction margins, indicating an intense period of strain release due to successive earthquakes, followed by long periods of seismic quiescence." This finding has applications to the seismic hazard of these regions, as it highlights the potential for future damaging earthquakes and tsunamis at active subduction margins with no measurable recent uplift. In such cases, paleoshorelines older than 10,000 years could provide an important constraint for hazard analysis. In other words: To assess the likelihood of future great quakes it will help to look at paleoshorelines.Further, it alerts scientists that earthquake clustering may not only characterise shallow faulting and smaller-sized earthquakes with magnitudes lower than M7 but it is a property of large subduction earthquakes.This work presents a conceptual model in which strain is released by temporally clustered great-earthquakes that rupture faults within the upper-plate as opposed to the zone where the tectonic plates meet (plate-interface). Onno Oncken of GFZ comments: "This is an intriguing finding that changes the stereotype view that all or most great subduction earthquakes occur along the active contact, i.e. plate-interface, of the two converging plates. We hope that this new finding will promote the mapping and discovery of such faults along active subduction margins and will also help explain the variability in the recurrence of great-earthquakes encountered on many subductions globally." | Earthquakes | 2,016 |
October 13, 2016 | https://www.sciencedaily.com/releases/2016/10/161013151146.htm | Geologist explores minerals below Earth's surface | A Florida State University geology researcher is going deep below Earth's surface to understand how some of the most abundant minerals that comprise Earth's crust change under pressure. | In a paper published today in "I am interested in exploring these materials at extreme conditions," Mookherjee said. "Feldspar is very abundant in Earth's crust so we need to understand its elastic property."Mookherjee's work shows that at a depth of about 30 kilometers from Earth's surface, feldspar decomposes to denser mineral phases such as pyroxene and quartz. The densification of feldspar could partially explain a scientific observation called seismic discontinuity across Earth's crust and mantle.This seismic discontinuity, also called Mohorovicic discontinuity, is the boundary between Earth's crust and mantle. It was first observed in 1909 by a Croatian scientist Andrija Mohorovicic who realized that seismograms from shallow-focus earthquakes had two sets of waves -- one that followed a direct path near Earth's surface, i.e., crust, and the other arriving faster and probably refracted from the underlying higher-velocity medium mantle."This is the first study of the elastic properties of feldspar at high pressure," Mookherjee said. "And it provides very new insight and a novel way of accounting for the sharp Mohorovicic discontinuity."Scientists have been working since the late 1950s to understand the Mohorovicic discontinuity that separates Earth's outermost layer -- oceanic and continental crust -- with the underlying mantle. Last year, researchers from the drill ship JOIDES Resolution made attempts to drill a bore hole across the discontinuity, but fell short. Further drilling attempts are planned for future."We care about the mineral structures in the deep Earth and how they transform to denser crystal structures within Earth," Mookherjee said. "Through a thorough understanding of the atomic scale structures at extreme conditions and how they influence the properties of Earth materials, it is possible to gain valuable insight into deep Earth dynamics." | Earthquakes | 2,016 |
October 6, 2016 | https://www.sciencedaily.com/releases/2016/10/161006101026.htm | Exhaling Earth: Scientists closer to forecasting volcanic eruptions | On average, 40 volcanoes on land erupt into the atmosphere each month, while scores of others on the seafloor erupt into the ocean. A new time-lapse animation uniting volcanoes, earthquakes, and gaseous emissions reveals unforgettably the large, rigid plates that make the outermost shell of Earth and suggests the immense heat and energy beneath them seeking to escape. | With one click, visitors can see the last 50 years of "Eruptions, Earthquakes, and Emissions." Called E3, the app allows the viewer to select and learn about individual eruptions, emissions, and earthquakes as well as their collective impact. Visualizing these huge global datasets together for the first time, users can speed or slow or stop the passage of time. They can observe flat maps or globes, and watch gas clouds circle the planet. Data from Smithsonian's Global Volcanism Program and the United States Geological Earthquake Survey (USGS) feed into the app, and the datasets are available for free download. The app will update continuously, accumulating new events and additional historical information as it becomes available."Have you had a 'eureka!' moment where you suddenly see order in what appeared chaotic? This app abounds in such moments," said Elizabeth Cottrell, head of the Global Volcanism Program of the Smithsonian Institution in Washington, DC. "As geologic events accumulate over time, Earth's tectonic plates appear before your eyes. What took geologists more than 200 years to learn, a viewer learns in seconds. We wanted to share the excitement with as big an audience as possible. This is the first time we're able to present these datasets together for the public."She added, "This app is interesting not only for educators and the public, but also will help scientists understand global eruption patterns and linkages between Earth's inner workings and the air we breathe."A team of experts developed the app with support from the Smithsonian Institution and the Deep Carbon Observatory, an international multidisciplinary research program exploring the quantities, movements, forms, and origins of carbon deep inside Earth. Deep Carbon Observatory scientists are studying volcanic emissions as part of this mission, and will more than triple the number of permanent volcano gas monitoring stations from 2012-2019.Hundreds of millions of people around the world live on the flanks of active volcanoes, and eruptions can cause massive economic damage even when few people live nearby. In 2010, Eyafjallajökull erupted in Iceland, spewing massive ash clouds, disrupting air travel for millions of people and costing the airline industry nearly USD 2 billion. Better anticipation of eruptions could lower the human and economic toll of these natural phenomena.Recent discoveries by Deep Carbon Observatory (DCO) scientists in the Deep Earth Carbon Degassing (DECADE) initiative are laying the foundation for improved volcanic eruption forecasts. These hard-won advances required expensive, dangerous expeditions to sniff gas emissions for clues."We are deploying automated monitoring stations at volcanoes around the world to measure the gases they emit," said Tobias Fischer, a volcanologist at the University of New Mexico, USA, and leader of DECADE. "We measure carbon dioxide, sulfur dioxide, and water vapor (steam), the major gases emitted by all volcanoes on the planet. In the hours before an eruption, we see consistent changes in the amount of carbon dioxide emitted relative to sulfur dioxide. Keeping an eye on the ratios globally via satellites and on-site monitoring helps us learn the precursors of volcanic eruptions. Monitoring these volcanic gas variations also helps us come up with a more accurate estimate of total volcanic carbon dioxide emissions on Earth -- a major goal of DCO.""Our goal of tripling the number of volcanoes monitored around the world by 2019 is no small task," added Fischer. "Installing instruments on top of volcanoes is dangerous work in extremely hard-to-reach places.""Sometimes our monitoring stations become victims of eruptions they are trying to measure, as happened recently on Villarrica volcano in Chile. At least our instruments recorded gas composition changes right up until the eruption destroyed them," Fischer noted.By 2019, DECADE scientists hope to have gas monitoring stations on 15 of the world's 150 most active volcanoes. This will add to the eight stations currently operated by other entities such as the USGS and the University of Palermo (Italy). Data collected at these monitoring stations are feeding a new database of volcanic carbon emissions, making potentially life-saving information available to many more scientists around the world.DCO volcanologists are also advancing basic knowledge about how different volcanoes work, which is further advancing eruption forecasting.Maarten de Moor and his team at the National University in Costa Rica, for example, using DECADE monitoring stations, have measured gas emissions at Póas and Turrialba volcanoes in Costa Rica over several years. De Moor and colleagues have observed remarkable changes in gas compositions before eruptions at these volcanoes, both of which have a huge impact on local society. Turrialba, for example, deposited ash on the capital city of San José over the last few weeks, affecting about 3 million people and closing the international airport."We're getting more and more confident that changes in the carbon to sulfur ratio precede eruptions," said de Moor. "Potentially, we can now see an eruption coming just by looking at gas emissions. What is truly fascinating is how dynamic these volcanoes are in their degassing and eruptive behavior. To understand the big picture of Earth degassing, we also need to understand the processes driving temporal variations in volcanic emissions."Historically, volcanologists have measured emissions of smelly sulfur dioxide much more easily than colorless, odorless carbon dioxide emissions. But DCO scientists at Centre National de la Recherche Scientifique (CNRS) and Université de Lorraine in France are designing new geochemical tools to detect and monitor large-scale emissions of volcanic carbon dioxide. Tools include a new high-precision method for measuring excess airborne amounts of a rare form of helium found in magma, high-temperature fluids from below Earth's crust that come out of volcanoes in the form of lava and gases."Our helium data suggest that even when they are not erupting, volcanoes constantly release carbon dioxide and other gases through the crust, from magma chambers deep underground," said Bernard Marty, leader of the CNRS group. "We see low level release of carbon dioxide over large areas surrounding Mt. Etna volcano in Sicily and Erta Ale volcano in Afar, Ethiopia, which tells us this might be happening at sites around the world."To assess volcanic activity and gas release on a global scale, DCO researchers at the University of Cambridge, UK, are taking yet another approach; measuring volcanic gases from space using satellites."While water vapor and carbon dioxide are much more abundant volcanic gases, sulfur dioxide is easier to measure because Earth's atmosphere contains very little sulfur dioxide," said Marie Edmonds, co-Chair of DCO's Reservoirs and Fluxes Science Community. "With satellites, we have been able to measure sulfur dioxide emissions for years and the technology keeps getting better. An exciting new aspect of DCO's research combines the satellite data with ground-based measurements of carbon to sulfur ratios provided by DECADE. This powerful combination allows us to better define global volcanic emissions, or degassing, of carbon dioxide.""DECADE's volcano-based instruments make it possible for us to ground-truth our satellite observations and obtain much more frequent measurements" added Edmonds. "Eventually we hope we'll get as accurate measurements from space as we do from the ground. When this happens, we can monitor volcanoes in remote parts of the world for a fraction of the cost and without risking scientists' lives." As the data accumulate, they too will stream into and through the E3 app. | Earthquakes | 2,016 |
October 4, 2016 | https://www.sciencedaily.com/releases/2016/10/161004135207.htm | Earthquake risk: New fault discovered in earthquake-prone Southern California region | A swarm of nearly 200 small earthquakes that shook Southern California residents in the Salton Sea area last week raised concerns they might trigger a larger earthquake on the southern San Andreas Fault. At the same time, scientists from Scripps Institution of Oceanography at the University of California San Diego and the Nevada Seismological Laboratory at the University of Nevada, Reno published their recent discovery of a potentially significant fault that lies along the eastern edge of the Salton Sea. | The presence of the newly mapped Salton Trough Fault, which runs parallel to the San Andreas Fault, could impact current seismic hazard models in the earthquake-prone region that includes the greater Los Angeles area. Mapping of earthquake faults provides important information for earthquake rupture and ground-shaking models, which helps protect lives and reduce property loss from these natural hazards.The National Science Foundation (NSF)-funded study appears in the Oct. 2016 issue of the journal "To aid in accurately assessing seismic hazard and reducing risk in a tectonically active region, it is crucial to correctly identify and locate faults before earthquakes happen," said Valerie Sahakian, a Scripps alumna, and lead author of the study.The research team used a suite of instruments, including multi-channel seismic data, ocean-bottom seismometers, and light detection and ranging, or lidar, to precisely map the deformation within the various sediment layers in and around the sea's bottom. They imaged the newly identified strike-slip fault within the Salton Sea, just west of the San Andreas Fault."The location of the fault in the eastern Salton Sea has made imaging it difficult and there is no associated small seismic events, which is why the fault was not detected earlier," said Scripps geologist Neal Driscoll, the lead principal investigator of the NSF-funded project, and coauthor of the study. "We employed the marine seismic equipment to define the deformation patterns beneath the sea that constrained the location of the fault."Recent studies have revealed that the region has experienced magnitude-7 earthquakes roughly every 175 to 200 years for the last thousand years. A major rupture on the southern portion of the San Andreas Fault has not occurred in the last 300 years."The extended nature of time since the most recent earthquake on the Southern San Andreas has been puzzling to the earth sciences community," said Nevada State Seismologist Graham Kent, a coauthor of the study and former Scripps researcher. "Based on the deformation patterns, this new fault has accommodated some of the strain from the larger San Andreas system, so without having a record of past earthquakes from this new fault, it's really difficult to determine whether this fault interacts with the southern San Andreas Fault at depth or in time."The findings provide much-needed information on the intricate structure of earthquake faults beneath the sea and what role it may play in the earthquake cycle along the southern end of the San Andreas Fault. Further research will help provide information into how the newly identified fault interacts with the southern San Andreas Fault, which may offer new insights into the more than 300-year period since the most recent earthquake."We need further studies to better determine the location and character of this fault, as well as the hazard posed by this structure," said Sahakian, currently a postdoctoral fellow at the U.S. Geological Survey's Earthquake Science Center. "The patterns of deformation beneath the sea suggest that the newly identified fault has been long-lived and it is important to understand its relationship to the other fault systems in this geologically complicated region."Scripps researcher Alistair Harding and Nevada Seismological Laboratory seismologist and outreach specialist Annie Kell also contributed to the study. | Earthquakes | 2,016 |
October 3, 2016 | https://www.sciencedaily.com/releases/2016/10/161003111456.htm | Strength of Earth's outer shell can be measured, weak spots pinpointed | An advanced imaging technique used to map Earth's outer shell also can provide a measure of strength, finding weak spots and magma upwellings that could point to volcanic or earthquake activity, according to a new study by geologists at the University of Illinois at Urbana-Champaign and the University of Adelaide in Australia. | The researchers developed a method for measuring strength and finding weak spots in the lithosphere, the outer layers of earth that include the crust and the outer mantle -- the molten rock lurking just under the surface that can well up and create volcanoes. The researchers found that calculating lithosphere strength using magnetotelluric imaging maps of the southwestern United States can more accurately describe the rough terrain and volcanic and seismic activity observed on the surface than can standard geologic models.The study by U. of I. geology professor Lijun Liu and Adelaide professor Derrick Hasterok is reported in the journal "According to plate tectonics, the standard theory of earth science, the lithosphere is supposed to be rigid. But we know that is not the case," Liu said. "We know that a lot of places like the western U.S. have frequent fault-slip earthquakes and very rough surface topography, and are tectonically active. In this paper, we propose a new way to describe the mechanical properties of Earth's lithosphere."Magnetotelluric imaging is a high-resolution mapping technique that the National Science Foundation has used to scan the lithosphere beneath much of the U.S. It provides information about the electrical conductivity of the lithosphere, which Liu and Hasterok were able to use to calculate strength and its variations from place to place."The same factors that affect electrical conductivity -- temperature, water content and the presence of molten material -- also affect the viscosity or strength. The hotter, wetter or more molten, the weaker the structure," Liu said.The detailed models produced using the MT imaging data of the southwestern U.S. more accurately portrayed surface structures at a scale of less than 100 kilometers, Liu said, which is important because features like volcanoes and faults are localized phenomena that are harder to predict using larger-scale models. The models depicted upwellings in the mantle and peaks in the topography that correlated to features in the terrain and active volcanoes.The researchers believe that analyzing lithosphere strength using MT images now being collected around the world can open new avenues of understanding the dynamic mechanisms of the Earth and its seismic activity."This method will aid our understanding of the processes that cause earthquakes and volcanic activity," Hasterok said. "We'll be able to see why earthquakes and volcanoes have occurred in the past and look for places where they might potentially happen in the future." | Earthquakes | 2,016 |
September 29, 2016 | https://www.sciencedaily.com/releases/2016/09/160929142759.htm | New technique for finding weakness in Earth's crust | Scientists have developed a method to estimate weakness in Earth's outer layers which will help explain and predict volcanic activity and earthquakes. | Published in the journal The research is a collaboration between researchers at the University of Illinois in the US and University of Adelaide in Australia.Geodynamic modelling relies on knowing the 'viscosity' or resistance to changing shape of Earth's outer layers."Producing realistic models of these movements has been difficult because the small scale variations in viscosity are often poorly known," says co-author Dr Derrick Hasterok, from the University of Adelaide's School of Physical Sciences."In essence, we've developed a method to estimate small scale (between one and 10 kilometer) variations of viscosity within the upper 400 km of Earth's crust using surface-based electromagnetic imaging techniques."The resulting model allows the dramatic improvement of flow models which can be used to make predictions about the forces driving tectonic plate deformation and sources of potential seismic and volcanic activity."This method will aid our understanding of the processes happening that cause earthquakes and volcanic activity," says Dr Hasterok. "We'll be able to see why earthquakes and volcanoes have occurred in the past and look for places where this might potentially happen in the future."The method they have developed uses an electromagnetic imaging technique called magnetotellurics to estimate the electrical conductivity beneath Earth's surface."The same factors which affect electrical conductivity ─ temperature, water content, and the presence of molten material (magma) ─ also affect the viscosity or strength. The hotter, wetter or more molten, the weaker the structure," says lead author Dr Lijun Liu, from the University of Illinois."We've been able to look at processes operating beneath Earth's surface at a much smaller scale than previous geodynamic modelling."The researchers used data from a magnetotelluric survery of western United States to show their model works. Currently there is a continent-wide project mapping the Australian upper mantle using the same electromagnetic technique, and the researchers believe applying this data to their new model will bring improved understanding of volcanic and earthquake activity along the southeastern and eastern coast of Australia. | Earthquakes | 2,016 |
September 28, 2016 | https://www.sciencedaily.com/releases/2016/09/160928094313.htm | Dense arrays of seismometers are letting scientists get a clearer look at a giant scar that underlies the American Midwest | When Doug Wiens approached Minnesota farmers to ask permission to install a seismometer on their land, he often got a puzzled look. "You could tell they were thinking 'Why are you putting a seismometer here?,' " said Wiens, professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis. "'We don't have earthquakes and we don't have volcanoes. Do you know something we don't?' " | Actually, he did. Deep beneath the fertile flat farmland, there is a huge scar in the Earth called the Midcontinent Rift. This ancient and hidden feature bears silent witness to a time when the core of what would become North America nearly ripped apart. If the U-shaped rip had gone to completion, the land between its arms -- including at least half of what is now called the Midwest -- would have pulled away from North America, leaving a great ocean behind.Weisen Shen, a postdoctoral research associate with Wiens, will be presenting seismic images of the rift at the annual meeting of the Geological Society of America (GSA) Sept. 25-28. The images were made by analyzing data from Earthscope, a National Science Foundation (NSF) program that deployed thousands of seismic instruments across America in the past 10 years.The Midcontinent Rift was discovered by geophysicists who noticed that gravity was stronger in some parts of the upper Midwest than in others. In the 1950s and 1960s, they mapped the gravity and magnetic anomalies with airborne sensors. Shen is contributing to a session at the GSA dedicated to Bill Heinze, a geophysicist who helped discover and map the Midcontinent Rift.But understanding of the rift then stalled until 2003, when the NSF funded Earthscope, a program whose mission is to use North America as a natural laboratory to gain insight into how the Earth operates.As part of Earthscope, the Incorporated Research Institutions for Seismology (IRIS) installed a network of 400 seismometers, called the USArray, that rolled across the United States from west to east, gathering data at each location for two years before moving on. USArray was installed on the West Coast beginning in 2004, and had advanced to the Midwest by 2010.Earthscope also made available a pool of seismometers, called the flexible array, for more focused field experiments. A consortium of universities, including Washington University in St. Louis, installed 83 of these stations along and across the rift in 2011, creating a dense array called SPREE.Seismologists had never before been able to blanket the landscape with seismometers in this way, and so the USArray has stimulated many innovations in the manipulation of the seismic data to extract information about Earth's crust and upper mantle.Seismic interpretation is a thorny version of what is called an inverse problem. If the Earth's interior were of uniform composition, seismic waves would travel in straight lines. But instead, underground structures or differences in temperature and density refract and reflect them. The problem is to figure out mathematically which obstructions could have produced the wave arrivals that the seismometers recorded.It's a bit like trying to figure out the shape of an island in a pond by throwing a pebble into the lake and recording the ripples arriving at the shore.The data wizard on the Washington University team is Shen, who has devised new techniques for combining many types of seismological data to create sharper images of Earth's interior.The farmers in Minnesota have a point when they wonder what an "earthquake sensor" could detect in an area where there are no earthquakes. The answer is that the seismometers record distant earthquakes, such as those on the Pacific Ring of Fire on the opposite side of the planet, and ambient noise, caused by activity such as powerful storms slamming into the Jersey Shore.Shen has seasoned the mix with several other measurements that can be extracted from the seismic record as well. By inverting all of these data functions simultaneously within a Bayesian statistical framework, he is able to obtain much clearer images of Earth's interior than one type of data alone would produce, together with estimates of the probability that the images are correct.What have the scientists learned about the rift?"When you pull apart a continent, like a piece of taffy, it starts to stretch and to thin," said Michael Wysession, professor of earth and planetary sciences and a member of the SPREE team. "And as it sags, the dip fills with low-density sediment."So if you go over a rift with a gravity sensor, you expect to find a negative gravity anomaly. Mass should be missing. But that's not what happened with the Midcontinent Rift. Instead of being thinner than the surrounding crust, it is thicker."We know that lava comes out at rifts," Wysession said. "The East African rift zone, for example, includes a number of active and dormant volcanoes, such as Mount Kilimanjaro. But the Midcontinent Rift was flooded with lava, and as it sank under the weight of the cooling basaltic rock, even more lava flowed into the depression."A huge volume of lava erupted here," Wysession said. "It was perhaps the largest outflowing of lava in our planet's history. And then, after the eruptions ended, the area was compressed by mountain building event to its east, thickening the scar by squeezing it horizontally.Shen published images of the rift made with USArray data in the Journal of Geophysical Research 2013. But at that time, he had only sparse coverage in the rift's vicinity. At the 2016 GSA meeting he will present images made with both USArray and SPREE data (especially many more "receiver functions," a type of seismic data that is particularly sensitive to seismic boundaries) that show what lies beneath the rift more clearly.Miles beneath the Earth's surface, there is a seismic boundary called the Mohorovičić discontinuity, or Moho. At the Moho, seismic waves hit higher density material and suddenly accelerate. But beneath the rift, Shen said, the Moho is blurred rather than sharp. "Its structure has been destroyed," he said.He also sees evidence of something called magmatic underplating. "We think magma might have trapped, or stalled out, at the Moho or within the crust during its rise to the surface," he said. This might explain why the Moho is so disrupted, although Shen can think of alternative explanations and expects there to be lively discussions at the GSA.He compares images of the Midcontinent Rift made with the SPREE array to images of the Rio Grande rift made with a similar seismic array called La Ristra. The La Ristra images show that the Rio Grande rift is thinner than the surrounding crust, not thicker. The Moho is clear and rises rather than sinks under the rift."I think we're looking at different stages of rifting," Shen said. The Rio Grande Rift is still active, still opening, but the Midcontinent Rift is already dead and has been squeezed shut.Wiens commented that the tremendous outpouring of magma at the Midcontinent Rift might also have disrupted its structure, making it look different from other rifts."My goal," Shen said, "is to provide basic seismic models of interesting tectonic regions like this one for geologists, geochemists and scientists from other disciplines to use -- to help them interpret their results and also help the public to better understand the story of the land they live on."Rural Minnesota is already onboard. "Some landowners were quite interested in what we were doing," Wiens said. "We got into one or two small town newspapers. 'So-and-so now has a seismometer on his farm,' the headline would read." | Earthquakes | 2,016 |
September 27, 2016 | https://www.sciencedaily.com/releases/2016/09/160927111442.htm | High-tech future early warning system for hurricanes, tornados and volcanic eruptions | Earlier this year, the Laser Interferometer Gravitational-Wave Observatory (LIGO) was able to detect a gravity wave wafting through space from two colliding black holes billions of years ago. | Now a group of researchers at Hendrix College in Conway, Arkansas has built a much smaller ring laser interferometer to explore how it could detect geophysical effects such as earthquake-generated ground rotation and infrasound from convective storms and have demonstrated the technology's potential as an early-warning system for natural disasters.Interferometers invented by Albert Michelson, who was awarded the 1907 Nobel Prize in physics for his work use a semi-transparent mirror to divide a beam of uniform light waves. Once divided, the different light waves are routed along different paths and then recombined. After recombination, an interference pattern of alternating bright and dark fringes is created. The fringes move in response to any changes between the two path lengths.More than 55 years later, ring laser interferometers were developed that could measure frequencies' proportional rotation instead of fringe shifts.This week in the"We essentially verified many of the results from a long-term study by the U.S. National Oceanic and Atmospheric Administration (NOAA) but we substituted a ring laser in place of microphones," said Robert Dunn, professor of physics at Hendrix College.The group's ring laser was able to "clearly show the frequency spectrum of the infrasound," he said. Specifically, they were able to detect infrasound from tornadoes 30 minutes before the tornado funnel was on the ground. The group also determined that infrasound from a tornado can travel 1,000 kilometers which confirms earlier studies by NOAA.How does their ring laser work? It's a bit complex, but to detect rotation via a ring laser, "a plasma tube projects a laser beam in both a clockwise and counterclockwise direction," Dunn explained. "If the laser cavity is rotating clockwise, it takes longer for a photon moving in the clockwise direction to go around the circumference of the cavity because it's chasing mirrors. Moving counterclockwise, the photon's path is shorter because it encounters mirrors. The speed of light is constant, so a path length difference exists between the beam moving clockwise vs. the one moving counterclockwise. The path length difference in turn creates a frequency difference."When the clockwise and counterclockwise beams are combined, "it creates a 'beat note' that's proportional to rotation," he continued. "Earth is always rotating, so a horizontal ring laser mounted away from the equator will measure its rotation."Phenomena that perturb or disturb the laser cavity modify Earth's beat frequency."This means that infrasound entering the laser cavity perturbs it and will frequency-modulate the beat note produced by Earth's rotation," Dunn explained."The detection of infrasound 30 minutes before a tornado is on the ground, in conjunction with Doppler radar, could prove very useful as an early warning system," Dunn pointed out. "And the ability to detect the rotational components of earthquake-generated seismic waves may help reduce the damage from earthquakes … because building codes often neglect the effects of ground rotation."Beyond tornado early warning systems, ring lasers can also detect infrasound from hurricanes and volcanoes."Volcanic ash can destroy jet engines, so the ability of an array of ring lasers to detect volcanic eruptions in remote locations like the Aleutian Islands could help to ensure the safety of commercial aircraft that regularly fly over the region," he added.Dunn stressed that, at this point, all of their results "must be considered preliminary," and that the group's goal is to "continue exploring how ring lasers can help reduce the impact of natural hazards." | Earthquakes | 2,016 |
September 22, 2016 | https://www.sciencedaily.com/releases/2016/09/160922161242.htm | Resonance in Rainbow Bridge | Utah's iconic Rainbow Bridge hums with natural and human-made vibrations, according to a new University of Utah study, published September 21 in | "Rainbow Bridge is constantly on the verge of stability," Moore says. "It's at this delicate balance, and it's worth trying to understand what forces play a role in accelerating the demise of such sensitive and exceptional natural features."Rainbow Bridge, located in southern Utah, is a sandstone formation arching over a side canyon of the Lake Powell reservoir. At nearly 300 feet from the canyon floor to the apex of the arch, Rainbow Bridge is one of the highest natural bridges in the world. The site is also revered as sacred by five nearby Native American nations, and visitors are asked not to walk under the bridge out of respect.With permission from tribal groups obtained by the National Park Service, Moore and his team monitored Rainbow Bridge to determine its modes of vibration, or predominant movements that together make up the vibration of the bridge. "A mode is the pattern of vibrational motion at a given frequency," Moore says. "Think of a guitar string. When you pluck a guitar string you generate one main tone plus several overtones on top of that. Those are all different modes."He and his team placed two seismic sensors on the bridge and two at a nearby location for reference comparison. Moore had conducted similar studies on other rock arches, seeking to understand how arches vibrate and what kinds of vibrational energy can cause resonance in the rock structures.Every object, including buildings, bridges, and rock arches, resonates at preferred frequencies. If the object feels vibrational energy at its resonant frequencies, then the motion of the object amplifies the vibrational waves -- sometimes to the point of damage. Resonant frequencies are well-known for human-made objects, but are more difficult to calculate for natural structures, such as Rainbow Bridge. The team recognized the rare opportunity to study the revered site. "We had a real respect for the bridge and the access we were permitted," Moore says.Over two days of seismic monitoring in March 2015, the team identified eight major modes of resonant vibration -- some forward and back, some up and down, and some twisting. Overall vibration of the bridge was a combination of those modes. Most of the time the bridge just shivered at a low hum.Several human-caused events contributed to resonance, however. Mode 1, for example, a forward and back bending motion, resonates at a frequency of around 1.1 Hertz -- about the same frequency as the waves of Lake Powell. Vibrations from those waves travel through the rock and are felt in Rainbow Bridge.The bridge also feels earthquakes. During the study period, the team recorded three earthquakes (listen to one of them in the accompanying audio file). Two of the earthquakes were local, but one, likely an induced earthquake, occurred in Oklahoma -- a testament, Moore says, that human activities can have unanticipated consequences. "Many things we do are actually felt by Rainbow Bridge, which is extremely remote," he says. "Human activity has altered Earth's vibrational wavefield." It's unclear what effect these low-level vibrations have on sensitive structures, or how they compare with natural vibrations caused by forces such as wind. "Recording that is an interesting outcome," Moore says.While Moore's team conducted seismic monitoring, Jack Wood of the National Park Service took photos of the bridge from countless vantage points, allowing the team to construct a 3D model of Rainbow Bridge that can be viewed here.From the model, the researchers were able to estimate the weight of the bridge at around 110,000 tons. According to Moore, that's about the same as a Nimitz-class aircraft carrier or a large cruise ship.Moore says the team's work is an impetus for further study of Rainbow Bridge, since so little is known about how vibration and resonance affect the health of the bridge. A repeated experiment would allow for comparison of the bridge's vibrational modes with the baseline established in this study as a way to assess whether the bridge is undergoing changes."We hope to provide a new way for people to look at the bridge as a dynamic, lively feature that's constantly vibrating and constantly moving," Moore says. "You get a new understanding of the bridge as a living feature rather than a static structure." | Earthquakes | 2,016 |
September 22, 2016 | https://www.sciencedaily.com/releases/2016/09/160922150659.htm | Research finds way to make fracking safer | Injecting wastewater deep underground as a byproduct of oil and gas extraction techniques that include fracking causes human-made earthquakes, the lead author of new research from Arizona State University said Thursday. | The study, which also showed that the risk can be mitigated, has the potential to transform oil and gas industry practices, ASU geophysicist Manoochehr Shirzaei said, calling the findings "very groundbreaking" and "very new.""It's a hot topic" because "injection and fracking is extremely important in terms of jobs, money and independence," Shirzaei, an assistant professor in the School of Earth and Space Exploration, said.The technique to extract oil and gas from rock using a high-pressure mix of water, sand or gravel and chemicals produces lots of wastewater, he said. This wastewater is disposed of through underground injections that "have led to an increase in earthquakes across the United States," he said."So now the goal, the scope of every scientist across the U.S.A., and maybe abroad, is to make that injection safer" by "reducing the number of earthquakes as much as we can," he said, explaining why the research was done.Shirzaei was careful to say that the injection of wastewater can come from processes associated with oil and gas extraction other than hydraulic fracturing.He said the study, published in the journal Shirzaei said he already has plans to present the findings to state and industry leaders in Texas and Colorado. He said that no one from the oil and gas industry has seen the work because researchers wanted to maintain their independence.The research could help reduce quakes like those felt recently in east Texas, which hasn't experienced such seismic activity historically. In May 2012, a 4.8 magnitude quake hit Timpson -- the largest ever monitored in the region. Several more temblors hit the area over the next 16 months.The quakes marked a significant increase in east Texas and in areas of the U.S. where unprecedented volumes of wastewater are being shot into deep geological formations.About 2 billion gallons of wastewater get injected underground every day into about 180,000 disposal wells in the U.S., mainly in Texas, California, Oklahoma and Kansas, according to the official news release.For the study, Shirzaei and co-authors William Ellsworth of Stanford University, Kristy Tiampo of the University of Colorado Boulder, Pablo González of the University of Liverpool (UK), and Michael Manga of UC Berkeley focused on four high-volume wells used for disposing wastewater near the epicenter for the Timpson, Texas, earthquake, the release said.The researchers used space-borne Interferometric Synthetic Aperture Radar (InSAR), a remote satellite-based sensing technique, to measure the surface uplift of the area near the wells, the release said."Monitoring surface deformation using these remote sensing techniques is a proactive approach to managing the hazards associated with fluid injection, and can help in earthquake forecasting," Shirzaei said, according to the release. "Our study reports on the first observations of surface uplift associated with wastewater injection."The researchers then calculated the strain and pore pressure underneath the wells that resulted in the uplift and, in turn, triggered the earthquakes, the release said. The research found that seismic activity increased, even when water injection rates declined, due to pore pressure continuing to diffuse throughout the area from earlier injections, the release said.InSAR uses a highly accurate radar to measure the change in distance between the satellite and ground surface, allowing the team to show that injecting water into the wells at high pressure caused ground uplift near the shallower wells, the release said.In addition, the data show less seismic activity in denser rock where pore pressure was prevented from disseminating into basement rock, helping to explain why injection can, but does not always, cause earthquakes, the release said.By integrating seismic data, injected water histories, and geological and hydrogeological information with surface deformation observations, the researchers have provided a definitive link between wastewater injection and earthquake activity in Texas, helping explain why injection causes earthquakes in some places and not others, the release said."This research opens new possibilities for the operation of wastewater disposal wells in ways that could reduce earthquake hazards," Shirzaei said, in the release. | Earthquakes | 2,016 |
September 15, 2016 | https://www.sciencedaily.com/releases/2016/09/160915085546.htm | Taking a fault's temperature | Ever think about taking a fault's temperature? What would you learn? A unique experiment where temperature was continuously measured for nearly a year inside the fault that made the catastrophic 2011 magnitude 9.0 Japan Earthquake reveals the thermal signature of pulses of water squirting out of fractures in response to other earthquakes on neighboring faults. | The experiment required measurements more than 7 km (4.5 miles) beneath the sea surface in a borehole observatory stretching nearly a kilometer (more than a half mile) underground as part of the Integrated Ocean Drilling Program's Japan Trench Fast Drilling Project.The results illustrate how water pressure within fault zones, which influences the susceptibility of faults to slip, can be disturbed by earthquakes on other faults. The observation of interactions between faults during the aftermath of a major earthquake helps scientists gain a better understanding of the processes that control earthquake occurrence.The research, supported by a grant from the Gordon and Betty Moore Foundation, was conducted by researchers from Texas A&M University and the University of California Santa Cruz. | Earthquakes | 2,016 |
September 12, 2016 | https://www.sciencedaily.com/releases/2016/09/160912132306.htm | Stalagmites in Indiana cave may record past earthquakes | Stalagmites rising from the floor of a cave in southern Indiana may contain traces of past earthquakes in the region, according to a report published September 13 in the | The rock formations in Donnehue's Cave, and others like them in local caves, could help scientists better understand the history of ancient seismic events in the Wabash Valley fault system of the Midwestern United States, said Samuel Panno, a University of Illinois and Illinois State Geological Survey researcher.However, the stalagmites also contain traces of past climate events such as glacial flooding, and the BSSA study by Panno and his colleagues demonstrates the importance of untangling climate and seismic effects on stalagmite growth.Stalagmites grow on cave floors from the accumulation of minerals that are precipitated from mineral-laden waters that drip from a cave ceiling. During this process, small to large stalactites that hang like icicles on the cave ceiling grow in the same manner. Earthquakes can leave their mark on stalagmites by shifting the ground in a way that changes the flow of the drip feeding the stalagmite -- closing a crack through which the drip flowed, for instance, or knocking down a stalactite that fed a stalagmite."Then when you take a stalagmite and slice it down its middle the long way and open it up like a book," Panno explained, "you can see these shifts in the axis of its growth."Using a variety of dating techniques to determine the age of the stalagmite and any surrounding sediments, scientists can then pinpoint the timing of these growth shifts and compare them to the timing of known earthquakes in an area.Among the four Donnehue stalagmites in the study, the research team found a twin stalagmite pair that had stopped growing around 100,000 years B.P. and then resumed growing at around 6000 years B.P., overlapping in time with a magnitude 7.1 to 7.3 earthquake in the area. Another younger stalagmite began growing around 1800 years B.P. -- coinciding with a magnitude 6.2 earthquake -- and showed later shifts in its growth axis that overlap with other seismic events in the nearby New Madrid Seismic Zone.These older earthquakes are known from other studies of soil shaking triggered by earthquakes, called paleoliquefaction, in ancient sediments. But seismic signs contained within stalagmites could potentially extend the evidence for these historic and prehistoric earthquakes, Panno said."Most of the evidence for paleoearthquakes comes from liquefaction features that are fairly easy to date," he noted. "The problem is that you are doing this in sediments that are usually on the order of several hundred to up to 20,000 years old, so to go beyond that, to get older and older earthquake signatures, we decided to look into caves."Stalagmite growth can also be affected by climate change, whether through drying up a drip source or through flooding that can block drip passages, or by smothering or dislodging growing stalagmites. Most of the stalagmites examined in the BSSA study were affected by climate-related events, Panno and his colleagues note.For instance, some of the stalagmites show shifts in growth patterns that coincide with known episodes of flooding from the melting of glacial ice, and others contain thin layers of silt deposited by these floods. "We're learning that you have to be really careful in where you sample these things, because the caves in southern Indiana, for example, tended to flood during the Pleistocene," Panno said. "That flooding can move a stalagmite or knock down the stalactite feeding it and change its drip location."Panno is working with U.S. Geological Survey seismologist John Tinsley at other caves in the Midwestern U.S., including Indiana's well-known tourist attraction Marengo Cave, to find other stalagmites, as well as related fallen stalactites that might bear signs of seismic history. They hope future studies will provide more solid evidence of how these formations could store information on the timing, magnitude and origin of past earthquake activity. | Earthquakes | 2,016 |
September 8, 2016 | https://www.sciencedaily.com/releases/2016/09/160908151116.htm | Earthquakes can trigger near-instantaneous aftershocks on different faults | According to a new study by scientists at Scripps Institution of Oceanography at the University of California San Diego, a large earthquake on one fault can trigger large aftershocks on separate faults within just a few minutes. These findings have important implications for earthquake hazard prone regions like California where ruptures on complex fault systems may cascade and lead to mega-earthquakes. | In the study, published in the Sept. 9 issue of the journal In one instance along the Sundra arc subduction zone, where the magnitude 9 Sumatra-Andaman mega-earthquake occurred off the coast of Indonesia in 2004, a magnitude 7 quake triggered two large aftershocks over 200 kilometers (124 miles) away. These aftershocks miles away reveal that stress can be transferred almost instantaneously by the passing seismic waves from one fault to another within the earthquake fault system."The results are particularly important because of their seismic hazard implications for complex fault systems, like California," said Fan, the lead author of the study. "By studying this type of triggering, we might be able to forecast hosting faults for large earthquakes."Large earthquakes often cause aftershock sequences that can last for months. Scientists generally believe that most aftershocks are triggered by stress changes caused by the permanent movement of the fault during the main seismic event, and mainly occur near the mainshock rupture where these stress changes are largest. The new findings show that large early aftershocks can also be triggered by seismic wave transients, where the locations of the main quake and the aftershock may not be directly connected."Multiple fault system interactions are not fully considered in seismic hazard analyses, and this study might motivate future modeling efforts to account for these effects," said Shearer, the senior author of the study. | Earthquakes | 2,016 |
August 25, 2016 | https://www.sciencedaily.com/releases/2016/08/160825151609.htm | X-raying the Earth with waves from stormy weather 'bombs' | Using a detection network based in Japan, scientists have uncovered a rare type of deep-earth tremor that they attribute to a distant North Atlantic storm called a "weather bomb." | The discovery marks the first time scientists have observed this particular tremor, known as an S wave microseism. And, as Peter Gerstoft and Peter D. Bromirski write in a related Perspective, their observation "gives seismologists a new tool with which to study Earth's deeper structure," one that will contribute to a clearer picture of Earth's movements, even those originating from the atmosphere-ocean system.Faint tremors called microseisms are phenomena caused by the sloshing of the ocean's waves on the solid Earth floor during storms. Detectable anywhere in the world, microseisms can be various waveforms that move through the Earth's surface and interior, respectively.So far, however, scientists analyzing microseismic activity in the Earth have only been able to chart P waves (those that animals can feel before an earthquake), and not their more elusive S wave counterpart (those that humans feel during earthquakes).Here, using 202 Hi-net stations operated by the National Research Institute for Earth Science and Disaster Prevention in Japan's Chugoku district, Kiwamu Nishida and Ryota Takagi successfully detected not only P wave microseisms triggered by a severe and distant North Atlantic storm, known as a weather bomb, but also S wave microseisms, too.What's more, the authors determined both the direction and distance to these waves' origins, providing insight into their paths as well as the earthly structures through which they traveled. In this way, the seismic energy travelling from this weather bomb storm through the Earth illuminated many dark patches of its interior. Nishida and Takagi's findings not only offer a new means by which to explore the Earth's internal structure, but they may also contribute to more accurate detection of earthquakes and oceanic storms. | Earthquakes | 2,016 |
August 24, 2016 | https://www.sciencedaily.com/releases/2016/08/160824212210.htm | Seismic shield: Large-scale metamaterials combat earthquakes in 3-D model | Numerical analysis considers both surface and guided waves, accounts for soil dissipation, and provides design guidelines for implementing earthquake protection using an array of ground-based cavities. | Metamaterials -- artificial structures that exhibit extraordinary vibrational properties -- could come to the rescue of regions threatened by earthquakes, according to new results published in the Today, large structures such as bridges and office blocks are protected against earthquakes through vibration isolation strategies. However, these approaches can be difficult to implement retrospectively, especially in historical buildings, and only apply locally. Shielding vulnerable structures using large-scale metamaterials -- which inhibit the propagation of incoming seismic waves through interference effects -- could help to protect a much wider area without any direct modification to existing buildings in the region.One of the simplest and most effective seismic shields proposed by the team involves digging 2-3 rows of equally spaced cross-shaped cavities in the ground. "The exact dimensions will depend on the soil type and the frequency range of the shield," explained Marco Miniaci of the Universities of Torino and Le Havre. "For sandy conditions and low-frequency seismic excitations, the width, spacing and depth of the cavities, which should be lined with concrete to prevent the surrounding soil from collapsing, could reach 10 metres."To extend the performance of the protective structure, the group proposes adding a number of smaller cylindrical cavities measuring 2m in diameter. There are other tweaks that can be applied too. By scaling down the size of the array, the shield's properties could be redirected towards similar problems occurring at higher frequency ranges. Scenarios include vibration prevention in the vicinity of high-speed train networks or heavy tramways. Blast protection could be another potential application."The next steps should involve experimental tests using scaled models in specialized geotechnical seismic and vibration labs," said Miniaci. "This would provide further validation of the proposed structures and help to build on earlier work in the field."Other researchers contributing to the project include Anastasiia Krushynska and Federico Bosia of the University of Torino, and Nicola Pugno of the University of Trento, FBK Trento and Queen Mary University of London. | Earthquakes | 2,016 |
August 24, 2016 | https://www.sciencedaily.com/releases/2016/08/160824140051.htm | Post-disaster optimization technique capable of analyzing entire cities | Some problems, says Paolo Bocchini, cannot be solved through intuition. | "If you are trying to solve a problem that has, say, ten possible outcomes -- you can probably find a way to figure out which one is optimal," says Bocchini, assistant professor of civil and environmental engineering at Lehigh University. "But what if the possible solutions number as high as 10 to the 120th power?"To illustrate the size of that figure, 10 to the 120th power, in long form, is written as a "1" followed by 120 zeroes.That is the massive number of possible recovery options with which civic leaders and engineers would be faced in the aftermath of a major catastrophic event, such as a hurricane or an earthquake."In a post-disaster recovery period, there may be one, large, very important bridge to repair that would take as long as a year to restore to full functionality," says Bocchini. "During that year, you could restore four smaller bridges which might have an even greater impact on getting the city back up and running. So, how do you figure out which choice is optimal?"He adds: "Computational models that predict what might work for one bridge or five bridges, simply don't work when you try to scale up to 100 bridges."To address this, Bocchini and his colleague Aman Karamlou, a doctoral assistant and structural engineering Ph.D. candidate, created a novel method that represents a major improvement in existing computational models and optimization methodologies. Their technique, Algorithm with Multiple-Input Genetic Operators -- or AMIGO, for short -- is described in a paper that was recently published in Designed to consider very complex objectives while keeping computational costs down, AMIGO makes the search process more efficient and expedites the convergence rate (the speed at which the sequence approaches its limit). It does this by taking advantage of the additional data in the genetic operators which are used to guide the algorithm toward a solution.In addition to being the first model to factor in so many elements, AMIGO is unique for its versatility."AMIGO takes the topology or characteristics of a network -- as well as the damage -- and then develops optimal recovery strategies. It can be used to solve a variety of scheduling optimization problems common in different fields including construction management, the manufacturing industry and emergency planning," says Bocchini.To demonstrate the effectiveness of their algorithm, Bocchini and Karamlou conducted a large-scale numerical analysis using an imagined earthquake scenario in the City of San Diego, California.They chose San Diego for the size of its transportation network -- it contains 238 highway bridges -- as well as its importance and value as a U.S. strategic port. The total value of the port's imports and exports in 2013 has been estimated to be more than $7 billion.The researchers identified the 80 bridges that would sustain the most serious damage based on the seismicity of the region, and used AMIGO to calculate the best restoration strategy.In a post-disaster situation, after the initial emergency response, those responsible for the recovery of a city or region must plan a repair schedule that balances mid-term and long-term recovery goals. Because every action will have an impact on the recovery, the trade-offs of each possible action must be considered.AMIGO is of the class of optimization solvers that uses what are called heuristic techniques and evolutionary algorithms that are inspired by the process of natural selection. These techniques are particularly useful for solving multi-objective optimization problems using a Pareto-based approach. The approach, which describes a method of assessing a set of choices, is named after Vilfredo Pareto (1848-1923), an Italian engineer and economist who used the concept in his studies of economic efficiency and income distribution.While the total number of feasible solutions in the imagined San Diego bridge network restoration scenario is considerably large, the results show that AMIGO managed to find a set of near optimal Pareto solutions in a small number of trials (about 25 generations).From the study: "Moreover, a new bridge recovery model is proposed. Compared to the previous studies, this recovery model is more realistic, as it takes advantage of the available restoration functions obtained by experts' surveys and scaling factors that account for the bridge cost."The researchers compared the performance of their optimization formulation with their previous optimization techniques. The results show significant improvement both in terms of optimality of the solution and convergence rate."This is of great importance, since for large realistic networks, the traffic analysis procedure can be computationally very expensive," they write. "Therefore, reducing the number of required generations for convergence can considerably affect the computational cost of the problem and make this approach finally applicable to real-size networks. Compared to previous formulations, the use of operational resource constraints and the new recovery model yield the generation of more realistic schedules."This paper was the first to be published under a project called Probabilistic Resilience Assessment of Interdependent Systems (PRAISys), a collaboration between Lehigh, Florida Atlantic University and Georgia State University. The team was awarded a grant of $2.2 million by the National Science Foundation (NSF) last year, as part of NSF's $20 million investment in new fundamental research to transform infrastructure." It is part of the Obama administration's "Smart Cities" initiative to help communities tackle local challenges and improve city services.The interdisciplinary Lehigh team -- led by Bocchini and made of up of faculty members with specialties in civil engineering, systems engineering, computer science and economics -- is looking at how interdependent systems work together during and after a disaster. The goal is to establish and demonstrate a comprehensive framework that combines models of individual infrastructure systems with models of their interdependencies for the assessment of interdependent infrastructure system resilience for extreme events under uncertainty using a probabilistic approach."In the post-disaster phase, leaders are faced with tough choices. The impact of each decision will affect so many other areas so it's important to go beyond looking at one system -- such as transportation -- and look at how they all work together," said Bocchini. | Earthquakes | 2,016 |
August 23, 2016 | https://www.sciencedaily.com/releases/2016/08/160823083555.htm | New insights into the relationship between erosion and tectonics in the Himalayas | Earth's climate interacts with so called surface processes -- such as landslides or river erosion -- and tectonics to shape the landscape that we see. In some regions, the sheer force of these processes has led scientists to believe that they may even influence the development of tectonics. An international team of researchers headed by the Cologne-based geographer Dr. Georgina King have now disproved this assumption. The results of their study, "Northward migration of the eastern Himalayan syntaxis revealed by OSL-thermochronometry," will appear in | In the eastern Himalaya, mountains exceeding 7,000 meters are coincident with extremely powerful rivers such as the Yarlung-Tsangpo, which is known as the "Everest of Rivers" and runs through the deeply incised Tsangpo gorge. "In this region the dramatic topography coupled with highly erosive rivers means that if surface processes can control tectonics, we should be able to record it here," says King.Dr. Georgina King heads the luminescence laboratory at the University of Cologne's Institute of Geography. She and her team used a new technique called luminescence thermochronometry to measure the cooling histories of rocks as they move towards the Earth's surface (exhumation). Their research revealed that surface processes do not control the location of tectonic deformation, but rather are responding to changing tectonics. The team measured the most recent stages of exhumation, that is, the final 1-2 km of the Earth's crust, which have risen to the surface over approximately the past 1 million years. In geological terms this is a quite recent period. The results show that in this time period, the rate of exhumation in the northward part of the eastern Himalayas increased. The scientists compared this record to plausible climatic and tectonic explanations. Using their data and data from other studies, they were able to show that this increased exhumation rate reflected tectonic changes and associated changes in river shape. "Our findings fit very well with previous hypotheses for this region, namely that there is tectonic, rather than climatic control over the pattern of erosion rates," King notes.Since surface processes can also influence the carbon cycle, this new research technique can also make valuable contributions to climate research. "As we improve our understanding of the role of surface processes in the dynamic evolution of mountains, it will give us insights into the associated carbon fluxes and how these influence global climate," King concludes. | Earthquakes | 2,016 |
August 22, 2016 | https://www.sciencedaily.com/releases/2016/08/160822174104.htm | Better understanding seismic hazards | The April 2015 Gorkha earthquake in Nepal killed more than 8,000 people and injured more than 21,000. With a magnitude of 7.8, it was the worst natural disaster to strike Nepal since the 1934 Nepal-Bihar earthquake. | Researchers Kelin Whipple, Manoochehr Shirzaei, Kip Hodges, and Ramon Arrowsmith of ASU's School of Earth and Space Exploration were quick to begin analyzing the data from this quake. Their findings have been recently published in The earthquake triggered numerous rock slides and avalanches, including one that obliterated the mountain village of Langtang, leaving few survivors. Elsewhere, entire villages were flattened by intense shaking, leaving thousands of people homeless and many hundreds missing."The days immediately after the earthquake were intense. We were very stressed by the rising death toll, and concerned for the many Nepalese guides and researchers we had worked with over the years," Whipple said.Despite the well-known association between seismic activity and mountain ranges, the Gorkha earthquake actually worked against long-term mountain building by uplifting the foothills and down-dropping the mountains. By studying this event and its counter-intuitive outcome, ASU researchers shed new light on the mechanisms of mountain building.The Himalaya, the most dramatic mountain range on Earth, is a manifestation of the ongoing collision between India and Asia. Exactly how the Himalaya were built, however, has long been debated.The conundrum is that major thrust faults that accommodate convergence between tectonic plates are usually relatively flat, tilted no more than a few degrees from horizontal, and thus do not produce much uplift.How, then, can we explain the existence of dramatic mountain ranges like the Himalaya?Some collisional mountain ranges grow because there are "ramps" or steep segments on major thrust faults that produce the rock uplift that builds high topography.In the Himalaya, the region of high topography is set back some 80 kilometers north of the active frontal thrust, leading to the conventional wisdom that the Himalaya grow by slip on a ramp beneath the High Himalaya. Whipple and colleagues realized that the Gorkha earthquake, while tragic, provided an opportunity to test this hypothesis.Even when seismic ruptures occur ~10 kilometers beneath the surface, as was the case of the Gorkha event, an earthquake causes patterns of deformation (uplift, subsidence and lateral shifts) that can reveal the geometry of the fault surface, or surfaces, involved.Using data from Global Positioning System (GPS) stations and Interferometric Synthetic Aperture Radar (InSAR) images collected during successive satellite fly-overs, ASU researchers were able to measure changes in surface elevation during a time period spanning the main Gorkha event, and several major aftershocks, with centimeter accuracy."Within hours of the event, it was clear from seismic data that the main rupture had occurred on a gently sloping thrust fault, but just 10 days later InSAR data was suggesting a more complex scenario -- and a possible resolution of an old debate," said Whipple.ASU researchers modeled these changes to show that the major active thrust fault remains relatively flat underneath the High Himalaya, inconsistent with the existence of the ramp often hypothesized to explain uplift of the range. This is fundamentally why the Gorkha earthquake actually uplifted the foothills and down-dropped the mountains.With the newly collected data, the researchers could see, in exquisite detail, physical evidence of a likely secondary rupture during the earthquake and its aftershocks that actually uplifted a portion of the High Himalaya northeast of Kathmandu. The secondary fault implicated is directly analogous to the fault responsible for the devastating 2005 Kashmir earthquake that claimed more than 85,000 lives in Pakistan.It appears that slip on this structure, and perhaps others like it, may contribute more to the continued growth of the mountains than large ruptures on the main active thrust fault. Interestingly, steep secondary thrusts may develop in response to rapid erosion focused in the High Himalaya.Ultimately, these findings not only provide a greater understanding of the mountain building process, they also may help anticipate seismic hazards in advance of devastating earthquakes by improving our ability to remotely identify active faults."To those that live at the foot of the Himalaya and other tectonically active mountain ranges, understanding the seismic hazard is of tantamount importance," said Whipple. | Earthquakes | 2,016 |
August 22, 2016 | https://www.sciencedaily.com/releases/2016/08/160822140520.htm | Some signs of induced seismicity spotted in Salton Trough's geothermal production fields | In some parts of Southern California's Brawley Seismic Zone, geothermal energy production may be increasing the background seismicity rate, but changes in earthquake rates elsewhere in the area seem to have natural causes, according to a report published online August 23 in the | Geothermal energy production in the Salton Trough's Brawley Seismic Zone does not have as dramatic of an impact on local seismicity as oil and gas production has had in parts of the central and eastern United States. There, the injection of massive volumes of wastewater from hydrocarbon production has increased the number of earthquakes and aftershocks in states like Oklahoma and Arkansas."It's difficult to broadly say that all the earthquakes that occur within a certain space and time at these Salton geothermal fields are going to be induced, because it's much more complicated than that," said U.S. Geological Survey (USGS) seismologist Andrea Llenos. "You have a lot of other natural processes here going on at the same time."After applying several models to investigate the earthquake behavior from two areas of geothermal production in the Brawley Zone, Llenos and her USGS co-author Andrew Michael concluded that geothermal production is connected to a significant increase in the background seismicity rate in the Salton Sea Geothermal Field (SSGF). The increase in the background rate at the SSGF occurred around 1988, coinciding with a "ramp-up" in geothermal operations in the field that may have led to a net depletion of fluids in the crust there.But Llenos and Michael found no clear connection between changes in seismicity and geothermal production in the North Brawley Geothermal Field (NBGF). They also found no significant increase in aftershocks in either field that could be connected to production.The seismologists developed their models using earthquake data collected from within 5 to 10 kilometers of each field, between 1975 and 2012 for the SSGF and 1980 and 2012 for the NBGF.Unlike the seismically quiet central U.S., the Salton Trough has long been the scene of significant seismic activity. The trough marks a transition between extensional rifting -- where the crust is stretching and thinning beneath the Gulf of California to the south -- to strike-slip motion along the San Andreas Fault system to the north. The area is prone to earthquake swarms, including an August 2012 swarm of more than 600 small earthquakes that occurred over two days near the town of Brawley.High heat flow through the crust in the Salton Trough makes it an attractive area for geothermal energy production, with four active geothermal fields that together generate more than 650 megawatts of power. Geothermal energy is produced when hot water is extracted from the ground as steam that powers generators. The water from the condensed steam is then injected back into the ground.At the time of the 2012 Brawley swarm, Llenos and Michael were finishing up a study of earthquake rate changes in Oklahoma and Arkansas, published in 2013, to evaluate whether those changes were induced by wastewater injection. "We wanted to see then if the tools we were using in the eastern and central U.S., which were working pretty well to distinguish natural and induced seismicity, would work as well or at all in the Salton Trough," Llenos explained.The energy production techniques differ considerably in the two regions. In the oilfields of Oklahoma, for example, the wastewater produced during oil recovery and injected back into the ground "increases the volume of fluids significantly at depth" Llenos said. "But for geothermal energy production, the field operators try to maintain a net fluid balance." In some fields, almost 90 percent of the fluids used in geothermal production get injected back into the ground shortly after they are extracted, Llenos noted.This difference may in part affect the production of aftershocks in each region, Llenos suggested. "In places like Oklahoma, the sudden changes in pressure at depth might bring many faults closer to their failure threshold," she said. "So if all these faults around an earthquake are closer to failure, we found that many more aftershocks are triggered as a result. We don't see that kind of drastic change in the Brawley Seismic Zone."Because the scientists had access to a much richer set of earthquake data in California than was available for the central U.S., "we were able to use more sophisticated models and tests here," Llenos said. "For example, we could analyze how aftershock triggering varies with distance between earthquakes much better here than we were able to in the central and eastern U.S."Since their 2013 study, however, more instruments have been placed and more seismicity data have been collected in the central U.S. "Now that there's more seismic network coverage in places like Oklahoma, we may someday be able to take the kinds of models we used here and reapply them in the central states," said Llenos. | Earthquakes | 2,016 |
August 19, 2016 | https://www.sciencedaily.com/releases/2016/08/160819120424.htm | 2014 Napa earthquake continued to creep, weeks after main shock | Nearly two years ago, on August 24, 2014, just south of Napa, California, a fault in Earth suddenly slipped, violently shifting and splitting huge blocks of solid rock, 6 miles below the surface. The underground upheaval generated severe shaking at the surface, lasting 10 to 20 seconds. When the shaking subsided, the magnitude 6.0 earthquake -- the largest in the San Francisco Bay Area since 1989 -- left in its wake crumpled building facades, ruptured water mains, and fractured roadways. | But the earthquake wasn't quite done. In a new report, scientists from MIT and elsewhere detail how, even after the earthquake's main tremors and aftershocks died down, earth beneath the surface was still actively shifting and creeping -- albeit much more slowly -- for at least four weeks after the main event. This postquake activity, which is known to geologists as "afterslip," caused certain sections of the main fault to shift by as much as 40 centimeters in the month following the main earthquake.This seismic creep, the scientists say, may have posed additional infrastructure hazards to the region and changed the seismic picture of surrounding faults, easing stress along some faults while increasing pressure along others.The scientists, led by Michael Floyd, a research scientist in MIT's Department of Earth, Atmospheric and Planetary Sciences, found that sections of the main West Napa Fault continued to slip after the primary earthquake, depending on the lithology, or rock type, surrounding the fault. The fault tended to only shift during the main earthquake in places where it ran through solid rock, such as mountains and hills; in places with looser sediments, like mud and sand, the fault continued to slowly creep, for at least four weeks, at a rate of a few centimeters per day."We found that after the earthquake, there was a lot of slip that happened at the surface," Floyd says. "One of the most fascinating things about this phenomenon is it shows you how much hazard remains after the shaking has stopped. If you have infrastructure running across these faults -- water pipelines, gas lines, roads, underground electric cables -- and if there's this significant afterslip, those kinds of things could be damaged even after the shaking has stopped."Floyd and his colleagues, including researchers from the University of California at Riverside, the U.S. Geological Survey, the University of Leeds, Durham University, Oxford University, and elsewhere, have published their results in the journal Floyd and co-author Gareth Funning, of UC Riverside, have been studying fault motions in northern California for the past seven years. When the earthquake struck, at about 3:20 a.m. local time, they just happened to be stationed 75 miles north of the epicenter."At the time, I did stir, thinking, 'C'mon, go back to sleep!'" Floyd says. "When we woke up, we turned on the news, figured out what happened, and immediately got back in our cars, picked up the instruments we had in the field, drove down the freeway to American Canyon, and started to put out instruments at sites we had measured just a few weeks before."Those instruments made up a network of about a dozen GPS receivers, which the team placed on either side of the fault line, as close to the earthquake's epicenter as they could. They left most of the instruments out in the field, where they recorded data every 30 seconds, continuously, for three weeks, to observe the distance the ground moved."The key difference between this study and other studies of this earthquake is that we had the additional GPS data very close to the epicenter, whereas other groups have only been able to access data from sites farther away," Floyd says. "We even had one point that was 750 meters from the surface rupture."The team combined its GPS data with satellite measurements of the region to reconstruct the ground movements along the fault and near the epicenter in the weeks following the main earthquake. They found that the fault continued to slip -- one side of the fault sliding past the other, like sandpaper across wood -- at a steady rate of several centimeters per day, for at least four weeks."The widespread and rapid afterslip along the West Napa Fault posed an infrastructure hazard in its own right," the authors write in the paper. "Repeated repairs of major roads crosscut by the rupture were required, and in some areas, water pipes that survived the [main earthquake] were subsequently broken by the afterslip."The earthquake and the afterslip took many scientists by surprise, as seismic data from the area showed no signs of movement along the fault prior to the main shock.Regarding the afterslip's possible effects on surrounding faults, the researchers found that it likely redistributed the stresses in the region, lessening the pressure on some faults. However, the researchers note that the afterslip may have put more stress on one particular region near the Rodgers Creek Fault, which runs through the city of Santa Rosa."Right now, we don't think there's any significantly heightened risk of quakes happening on other nearby faults, although the risk always exists," Floyd says.Curiously, the scientists identified a large region beneath the West Napa Fault, just northwest of Napa, which they've dubbed the "slip and aftershock shadow" -- a zone that was strangely devoid of any motion during both the earthquake and afterslip. Floyd says this shadow may indicate a buildup in seismic pressure."The fact that nothing happened there is almost more cause for concern for us than where things actually happened," Floyd says. "It would produce a fairly small quake if that area was to rupture, but there's just no knowing if it would continue on to start something more."Floyd says that in developing seismic hazard assessments, it's important to consider afterslip and slowly creeping faults, which occur often and over long periods of time following the more obvious earthquake."There are some earthquakes where we think we might be seeing some activity even 15 years after the main quake," Floyd says. "So the more examples of an earthquake happening followed by afterslip that we can study, the better we can understand the entire process." | Earthquakes | 2,016 |
August 18, 2016 | https://www.sciencedaily.com/releases/2016/08/160818090604.htm | The math of earthquakes | A UTEP computational science doctoral student has successfully tied a new mathematical modeling process to the study of earthquakes. | "The model that we applied to the earthquake data was originally applied to financial data," said Osei Tweneboah, who received his master's degree from UTEP in 2015. "Financial data is high frequency, which means there are a lot of fluctuations in the data. Earthquake data behaves like the financial data."After going through a variety of financial models to find a good fit, Tweneboah zeroed in on one called Ornstein-Uhlenbeck. His modeling will help analyze the effect that earthquakes from long ago have on present and future quakes. The hope is for better understanding of how tectonic stress decays and accumulates during long periods of time -- and to potentially estimate when an earthquake could happen.In May, Tweneboah presented his findings in a paper published in the journal | Earthquakes | 2,016 |
August 8, 2016 | https://www.sciencedaily.com/releases/2016/08/160808091256.htm | International ocean drilling expedition to understand causes of the Indian Ocean 2004 earthquake and tsunami | The devastating earthquake that struck North Sumatra and the Andaman and Nicobar Islands on Boxing Day (26 December) in 2004 caused a tsunami that inundated coastal communities around the Indian Ocean, killing over 250,000 people in 14 countries. That earthquake was caused by a slip on a subduction zone plate boundary fault beneath the eastern Indian Ocean. | Now, over the coming weeks, a team of international researchers are returning to offshore Sumatra to collect marine sediments, rocks and fluids from this particular zone for the first time to gain a better understanding of the materials and to collect data for predicting how they behave in fault zones to generate large earthquakes.Throughout August and September the researchers, including experts from Ocean and Earth Science at the University of Southampton will spend two months on board the drilling vessel JOIDES Resolution as part of the International Ocean Discovery Programme (IODP). The Expedition, number 362 of the IODP, involves 33 scientists and two educators from 13 countries including Professors Lisa McNeill and Tim Henstock from the University of Southampton. Professor McNeill is one of the Expedition leaders along with Associate Professor Brandon Dugan of the Colorado School of Mines and Dr Katerina Petronotis of the IODP."We are very excited that the project is about to start as it has taken many years of preparation and the dedication of a large team of scientists from around the world," said Professor McNeill. "We have an excellent team onboard and we hope the results will help us understand what controls the size of the very largest earthquakes on Earth, particularly following the enormous numbers of casualties due to subduction earthquakes and tsunamis in the last 10-15 years."The Boxing Day earthquake of 2004 and the Japan Tohoku-oki earthquake in 2011 both ruptured to much shallower depths than expected, producing very large earthquakes and tsunami, and prompting a re-evaluation of earthquake slip potential and of the properties of shallow subduction faults," Professor McNeill continued. "Subsequent large magnitude earthquakes have struck this margin since 2004, including unusually large earthquakes in the Indian plate offshore North Sumatra in 2012. Therefore developing a better understanding of earthquake and tsunami behavior and potential is a priority for local communities, for the wider Indian Ocean, and for related subduction zones."Professor McNeill explained that the North Sumatran subduction margin has an unusual structure and morphology that is likely influenced by the properties of the sediments and rocks forming the margin."Although our understanding of this margin's structure and development has increased enormously since 2004 due to marine geophysical data collection, as yet very little is known of the properties of the materials that make up this subduction zone," she continued. "This project will investigate how materials coming into the system drive shallow earthquake rupture and influence the shape of the continental margin. Our ultimate goal is to understand the hazard potential for this margin, and eventually others with similar material properties and margin morphology."This ocean drilling expedition will for the first time drill scientific boreholes within the sediments entering this subduction zone, including the layer of sediment that eventually develops into the earthquake-generating fault," Professor Henstock explained. "We know the sediments are of deep sea and terrestrial origin, including those eroded from the high Himalayas and transported thousands of kilometres into the Bay of Bengal and eastern Indian Ocean. But we do not know how the sediments change as they become physically and chemically altered as the sediment section builds up to 4-5 km thickness before reaching the subduction zone."Burial and increased temperatures also affect fluids within the sediment pile, and these are very important for earthquake fault behavior," Professor Henstock concluded. "Sampling and measuring the properties of the materials in situ and then extrapolating their properties to greater burial depths using modeling techniques and lab experiments will be important goals of this project." | Earthquakes | 2,016 |
August 5, 2016 | https://www.sciencedaily.com/releases/2016/08/160805230109.htm | Subduction zone earthquakes off Oregon, Washington more frequent than previous estimates | A new analysis suggests that massive earthquakes on northern sections of the Cascadia Subduction Zone, affecting areas of the Pacific Northwest that are more heavily populated, are somewhat more frequent than has been believed in the past. | The chance of one occurring within the next 50 years is also slightly higher than previously estimated.The findings, published this week in the journal The work was done by researchers from Oregon State University, Camosun College in British Columbia and Instituto Andaluz de Ciencias de la Tierra in Spain. The research was supported by the National Science Foundation and the U.S. Geological Survey."These new results are based on much better data than has been available before, and reinforce our confidence in findings regarding the potential for major earthquakes on the Cascadia Subduction Zone," said Chris Goldfinger, a professor in the College of Earth, Ocean and Atmospheric Sciences at OSU, and one of the world's leading experts on tectonic activity of this subduction zone."However, with more detailed data we have also changed somewhat our projections for the average recurrence interval of earthquakes on the subduction zone, especially the northern parts. The frequency, although not the intensity, of earthquakes there appears to be somewhat higher than we previously estimated."The Cascadia Subduction Zone runs from northern California to British Columbia, and scientists say it can be roughly divided into four segments. There have been 43 major earthquakes in the past 10,000 years on this subduction zone, sometimes on the entire zone at once and sometimes only on parts of it. When the entire zone is involved, it's believed to be capable of producing a magnitude 9.1 earthquake.It's been known for some time, and still believed to be accurate, that the southern portions of the subduction zone south of Newport, Oregon, tend to rupture more frequently -- an average of about every 300-380 years from Newport to Coos Bay, and 220-240 years from Coos Bay to Eureka, California.The newest data, however, have changed the stakes for the northern sections of the zone, which could have implications for major population centers such as Portland, Tacoma, Seattle and Vancouver, B.C.A section of the zone from Newport to Astoria, Oregon, was previously believed to rupture on average about every 400-500 years, and that average has now been reduced to 350 years. A section further north from Astoria to Vancouver Island was previously believed to rupture about every 500-530 years, and that average has now been reduced to 430 years.The last major earthquake on the Cascadia Subduction Zone -- pinpointed in time because it caused a tsunami that raced all the way across the Pacific Ocean to Japan -- occurred in January, 1700, more than 315 years ago."What this work shows is that, contrary to some previous estimates, the two middle sections of the Cascadia Subduction Zone that affect most of Oregon have a frequency that's more similar than different," said Goldfinger, who directs the Active Tectonics and Seafloor Mapping Laboratory at OSU.Based on these findings, the chances of an earthquake in the next 50 years have also been slightly revised upwards. Of the part of the zone off central and northern Oregon, the chance of an event during that period has been changed to 15-20 percent instead of 14-17 percent. On the furthest north section of the zone off Washington and British Columbia, the chance of an event has increased to 10-17 percent from 8-14 percent.The study also increased the frequency of the most massive earthquakes, where the entire subduction zone ruptures at once. It had previously been believed this occurred about half the time. Now, the data suggest that several partial ruptures were more complete than previously thought, and that complete ruptures occur slightly more than half the time."Part of what's important is that these findings give us more confidence about what's coming in our future," Goldfinger said."We believed these earthquakes were possible when the hypothesis was first developed in the late 1980s. Now we have a great deal more certainty that the general concern about earthquakes caused by the Cascadia Subduction Zone is scientifically valid, and we also have more precise information about the earthquake frequency and behavior of the subduction zone."Based in part on the growing certainty about these issues, OSU has developed the Cascadia Lifelines Program, an initiative working with Pacific Northwest business and industry to help prepare for the upcoming subduction zone earthquake, mitigate damage and save lives. Many other programs are also gaining speed.The new measurements in this research were made with cores that showed the results of massive amounts of sediments released by subsea landslides during a subduction zone earthquake -- a catastrophic event beneath the sea as well as on land. New technology is helping researchers to actually simulate these underwater landslides, better understand their behavior, and more accurately identify the "turbidite" or sediment layers they leave behind.The large amounts of additional data, researchers say, has helped refine previous work, fill holes in the data coverage, and also to rule out other possible causes of some sediment deposits, such as major storms, random landslides or small local earthquakes. | Earthquakes | 2,016 |
August 1, 2016 | https://www.sciencedaily.com/releases/2016/08/160801113957.htm | The search for the earthquake nucleus | Where a tectonic plate dives under another, in the so-called subduction zones at ocean margins, many strong earthquakes occur. Especially the earthquakes at shallow depths often cause tsunamis. How exactly are such earthquakes initiated? Which rock composition favours a break in the earth's interior that can lead to such natural disasters? Scientists at GEOMAR Helmholtz Centre for Ocean Research Kiel and the University of Utrecht (NL) published a study in the scientific journal | The effects of earthquakes are often severe and highly visible. They can destroy homes, induce slope failures and trigger tsunamis. The main cause for earthquakes are the stresses that occur in the Earth's interior, when two tectonic plates pass each other and interlock during this process. But even the worst earthquake starts with a very small first crack in the rock from which a large fracture can develop. So far it was assumed that initial cracks for earthquakes mainly occur in clay-rich sediments. Scientists at GEOMAR Helmholtz Centre for Ocean Research Kiel and the University of Utrecht (NL) were now able to prove that under certain conditions calcareous sediments are the most likely candidates for the first breakage of an earthquake. The study is published today in the international journal For their investigations the scientists used samples obtained during two expeditions in 2011 and 2012 with the US drillship JOIDES RESOLUTION off the coast of Costa Rica. There the Pacific Cocos plate is subducted beneath the Caribbean plate. In the past this has repeatedly led to severe earthquakes in this region. "The aim of the Costa Rica Seismogenesis Project (CRISP) was to obtain information about the structure of the subducting and the overriding plate using drill cores" Dr. Michael Stipp from GEOMAR, initiator and second author of the current research study, explains.During subduction the Cocos Plate carries its overlying sediments downwards, which are thus sandwiched between the plates. "Off the coast of Costa Rica, the seismogenic zone that is the zone where earthquakes are generated along the plate boundary, starts already in an exceptionally shallow depth of about five to six kilometres. This is right in these subducted sediments," Robert Kurzawski states, PhD student at GEOMAR and first author of the study.However, the sediments usually show variable compositions. Off the coast of Costa Rica and in most subduction zones in the tropical and subtropical area both clayey and calcareous sediment layers are found. Due to the drill cores obtained from JOIDES RESOLUTION the scientist could investigate samples exactly from these sediment layers. In the "Rock Mechanics Laboratory" of the University of Utrecht they brought the samples to conditions that prevail at depth, where shallow earthquakes occur. "These conditions include an increased pressure, temperatures of about 100 degrees Celsius and finally shear movements," Dr. Stipp explains.Since the clay sediments are considered mechanically weak, it was assumed that the first cracks would be formed in these when the subsurface stresses are large enough. In the experiments, it became clear that the clay-rich sediments from Costa Rica in contrast to the calcareous sediments react less sensitive to changes in stress, temperature and especially pore pressure. The calcareous sediments, however, change their frictional properties significantly during the increase in temperature and pore pressure. "Exactly at the conditions which are expected for shallow earthquakes the chalks suddenly got unstable and weaker than the clayey material. With these properties the calcareous sediments form the predetermined breaking point in the rock sequence, " Robert Kurzawski explains.These results are particular interesting, because calcareous sediments are typical and widespread especially for tropical and subtropical oceans and thus occur at many subduction zones around the Pacific, but also in the Caribbean and Mediterranean Sea. "Of course we still do not know all the processes that can trigger earthquakes. But we have demonstrated by this study that material properties cannot simply be extrapolated from surface conditions to those at greater depth. Therefore, further drilling, especially in the framework of the International Ocean Discovery Program (IODP), is required to learn more about the earthquake processes at depth, " Michael Stipp concludes. | Earthquakes | 2,016 |
July 28, 2016 | https://www.sciencedaily.com/releases/2016/07/160728143525.htm | Earth's mantle appears to have a driving role in plate tectonics | Deep down below us is a tug of war moving at less than the speed of growing fingernails. Keeping your balance is not a concern, but how the movement happens has been debated among geologists. | New findings from under the Pacific Northwest Coast by University of Oregon and University of Washington scientists now suggest a solution to a mystery that surfaced when the theory of plate tectonics arose: Do the plates move the mantle, or does the mantle move the plates.The separation of tectonic plates, the researchers proposed in a paper online ahead of print in the journal The new idea is based on seismic imaging of the Endeavor segment of the Juan de Fuca Plate in the Pacific Ocean off Washington and on data from previous research on similar ridges in the mid-Pacific and mid-Atlantic oceans."Comparing seismic measurements of the present mantle flow direction to the recent movements of tectonic plates, we find that the mantle is flowing in a direction that is ahead of recent changes in plate motion," said UO doctoral student Brandon P. VanderBeek, the paper's lead author. "This contradicts the traditional view that plates move the mantle."While the new conclusion is based on a fraction of such sites under the world's oceans, a consistent pattern was present, VanderBeek said. At the three sites, the mantle's flow is rotated clockwise or counterclockwise rather than in the directions of the separating plates. The mantle's flow, the researchers concluded, may be responsible for past and possibly current changes in plate motion.The research -- funded through National Science Foundation grants to the two institutions -- also explored how the supply of magma varies under mid-ocean ridge volcanoes. The researchers conducted a seismic experiment to see how seismic waves moved through the shallow mantle below the Endeavor segment.They found that the middle of the volcanic segment, where the seafloor is shallowest and the inferred volcanic activity greatest, the underlying mantle magma reservoir is relatively small. The ends, however, are much deeper with larger volumes of mantle magma pooling below them because there are no easy routes for it to travel through the material above it.Traditional thinking had said there would be less magma under the deep ends of such segments, known as discontinuities."We found the opposite," VanderBeek said. "The biggest volumes of magma that we believe we have found are located beneath the deepest portions of the ridges, at the segment ends. Under the shallow centers, there is much less melt, about half as much, at this particular ridge that we investigated."Our idea is that the ultimate control on where you have magma beneath these mountain ranges is where you can and cannot take it out," he said. "At the ends, we think, the plate rips apart much more diffusely, so you are not creating pathways for magma to move, build mountains and allow for an eruption." | Earthquakes | 2,016 |
July 26, 2016 | https://www.sciencedaily.com/releases/2016/07/160726131806.htm | Earthquake-resilient pipeline could shake up future for aging infrastructure on west coast | A top engineer from the city of Los Angeles visited Cornell University this month as researchers tested a new earthquake-resilient pipeline designed to better protect southern California's water utility network from natural disasters. They ran multiple tests, including an earthquake simulation in which a 28-foot-long section of the pipe was outfitted with more than 120 monitoring instruments and buried within 80 tons of soil -- an experiment that took over a month for the research team to prepare. | The test mimicked a fault rupture that can occur during an earthquake when global plates begin to slip past each other, causing the ground to shift and deform. A large, hydraulically powered "split box" imposed 2 feet of fault rupture along a 50-degree angle, forcing the buried pipeline into a combination of compression and bending."The pipe was able to accommodate the 2 feet and didn't spring a leak," said Brad Wham, a geotechnical engineering postdoc from Cornell who designed the test, which was performed at the Cornell Geotechnical Lifelines Large-Scale Testing Facility. "We took the pipe to three times its current design standard, and it continued to convey water. So we consider it a successful test and very promising technology." And while the test pipe was only 8 inches in diameter, Wham says the results are scalable and could be applied to pipelines as large as 70 inches in diameter or greater."It surpassed expectations," said Tom O'Rourke, professor of civil and environmental engineering at Cornell University and the project's principal investigator.The steel pipe, developed by JFE Holdings in Japan, uses a unique structural wave design to control buckling, allowing the pipe to bend and compress without rupturing or losing water pressure. The wave features are installed at key locations along the pipeline to absorb large ground deformation, such as movements imposed by earthquakes and landslides or from undermining associated with scour during hurricanes and floods. The extent of its performance was unknown until it arrived at Cornell.The results are significant for Los Angeles and other West Coast cities that want to upgrade their aging utility systems, especially portions that cross over fault lines. Craig Davis, the resilience program manager for L.A.'s Department of Water and Power, attended the testing and said his city's water utility system -- the nation's largest -- crosses over 30 fault lines en route to supplying water to more than 4 million residents. The new pipe produced by JFE Holdings now gives Davis and other engineers a new option for securing water supply to the city's most vulnerable areas.Los Angeles is upgrading its water utility system through the "Resilience By Design" program implemented by Mayor Eric Garcetti, and other municipalities around the country are eager to initiate similar programs following natural disasters like Hurricane Katrina and Superstorm Sandy. "What we've actually seen is a paradigm shift in pipeline technology, and it's a market-driven research environment," said O'Rourke, who added that a steady stream of business from manufacturing companies like JFE Holdings has kept his facility in high demand. "All of the West Coast utilities say that if you want us to consider your pipe, you have to test it Cornell. Ours is the only facility in the world that can perform these kinds of tests."Following the fault rupture test, the research team spent three days carefully excavating the pipeline and will begin collecting additional data based on its deformation. The results will help officials identify the most strategic locations for the new pipeline to be installed."We modeled the Los Angeles water supply and have the entire system on a secure computer," said O'Rourke. "We created the next generation of hazard-resilient network modeling, and they actually used it to develop policy and emergency response operations."Los Angeles is not the only city to benefit from Cornell's unique testing facility. San Francisco has implemented fault rupture hazard solutions for pipelines validated by Cornell, with Portland, Seattle and Vancouver all considering upgrades based on recent test results. | Earthquakes | 2,016 |
July 26, 2016 | https://www.sciencedaily.com/releases/2016/07/160726131638.htm | Ancient temples in the Himalaya reveal signs of past earthquakes | Tilted pillars, cracked steps, and sliding stone canopies in a number of 7th-century A.D. temples in northwest India are among the telltale signs that seismologists are using to reconstruct the extent of some of the region's larger historic earthquakes. | In their report published online July 27 in The temples in the Chamba district of Himachal Pradesh, India lie within the Kashmir "seismic gap" of the Northwest Himalaya range, an area that is thought to have the potential for earthquakes magnitude 7.5 or larger. The new analysis extends rupture zones for the 1905 Kangra earthquake (magnitude 7.8) and the 1555 Kashmir earthquake (possibly a magnitude 7.6 quake) within the Kashmir gap.The type of damage sustained by temples clustered around two towns in the region -- Chamba and Bharmour -- suggests that the Chamba temples may have been affected by the 1555 earthquake, while the Bharmour temples were damaged by the 1905 quake, the seismologists conclude.The epicenter of the 1555 earthquake is thought to be in the Srinagar Valley, about 200 kilometers northwest of Chamba. If the 1555 earthquake did extend all the way to Chamba, Joshi said, "this further implies that the eastern Kashmir Himalaya segment between Srinagar and Chamba has not been struck by a major earthquake for the last 451 years."The stress built up in this section of the fault, Joshi added, "may be able to generate an earthquake of similar magnitude to that of the 2005 Kashmir earthquake that devastated the eastern Kashmir."That magnitude 7.6 earthquake killed more than 85,000 people, mostly in north Pakistan, and caused massive infrastructure damage.To better understand the historical earthquake record in the region, Joshi and Thakur examined several temples in the region to look for telltale signs of earthquake damage. It can be difficult at first to distinguish whether a tilted pillar, for example, is due to centuries of aging or to earthquake deformation.But Joshi noted that archaeoseismologists are trained to look for regular kinds of deformation to a structure -- damages "that have some consistency in their pattern and orientation," said Joshi. "In the cases of aging and ground subsidence, there is no regular pattern of damage."At the temples, the researchers measured the tilt direction, the amount of inclination on pillars and the full temple structures, and cracks in building stones, among other types of damage. They then compared this damage to historic accounts of earthquakes and information about area faults to determine which earthquakes were most likely to have caused the damage."In the Chamba-area temples, there are some marker features that indicate that the body of the temple structure has suffered some internal deformation," said Joshi. "The pillars and temple structures are tilted with respect to their original positions. The rooftop portions show tilting or displacement."Other earthquake damage uncovered by the researchers included upwarping of stone floors, cracked walls, and a precariously leaning fort wall."The deformation features also give some clues about the intensity of an earthquake," Joshi explained. "For example if a structure experiences a higher intensity XI or X, then the structure could collapse. But if the structure is not collapsed but it tilts only, then it indicates that the structure experienced lower intensity of IX and VIII."The Mercalli intensity scale is a measurement of the observed effects of an earthquake, such as its impact on buildings and other infrastructure. Scale measurements of VIII ("severe") and IX ("violent") would indicate significant damage, while higher scale measurements indicate partial to complete destruction of buildings, roads, and other infrastructure. | Earthquakes | 2,016 |
July 25, 2016 | https://www.sciencedaily.com/releases/2016/07/160725090232.htm | Magma build-up may put Salvadoran capital at risk | The build-up of magma six kilometres below El Salvador's Ilopango caldera means the capital city of San Salvador may be at risk from future eruptions, University of Bristol researchers have found. | A caldera is a large cauldron-like volcanic depression or crater, formed by the collapse of an emptied magma chamber. The depression often originates from very big explosive eruptions. In Guatemala and El Salvador, caldera volcanoes straddle tectonic fault zones along the Central American Volcanic Arc (CAVA). The CAVA is 1,500 kilometres long, stretching from Guatemala to Panama.The team, from the Volcanology research group at Bristol's School of Earth Sciences and the Ministry of the Environment and Natural Resources in El Salvador, studied the density distribution beneath the Ilopango caldera and the role tectonic stresses -- caused by the movement of tectonic plates along fault lines -- have on the build-up of magma at depth. Their study is published in the journal The Ilopango caldera is an eight km by 11 kilometre volcanic collapse structure of the El Salvador Fault Zone. The collapsed caldera was the result of at least five large eruptions over the past 80,000 years.The last of these occurred about 1,500 years ago and produced enough volcanic ash to form a 15 centimetre thick layer across the entire UK. This catastrophic eruption destroyed practically everything within a 100 kilometre radius, including a well-developed native Mayan population, and significantly disturbed the Mayan populations as far as 200 kilometres away.The most recent eruptions occurred in 1879-1880 and were on a much smaller scale than the previous one.Project leader and co-author Dr Joachim Gottsmann said: "Most earthquakes take place along the edges of tectonic plates, where many volcanoes are also located. There is therefore a link between the breaking of rocks, which causes faults and earthquakes and the movement of magma from depth to the surface, to feed a volcanic eruption. The link between large tectonic fault zones and volcanism is, however, not very well understood."Existing studies show that magma accumulation before a large caldera-forming eruption, as well as the caldera collapse itself, may be controlled by fault structures."However, it is unclear to what extent regional tectonic stresses influence magma accumulation between large caldera-forming eruptions.," co-author Professor Katharine Cashman said.Lead author Jennifer Saxby, whose research towards a MSc in Volcanology contributed to the study, said: "Addressing this question is important not only for understanding controls on the development of magmatic systems, but also for forecasting probable locations of future eruptive activity from caldera-forming volcanoes."The team discovered that the current tectonic stress field promotes the accumulation of magma and hydrothermal fluids at shallow (< 6km) depth beneath Ilopango. The magma contains a considerable amount of gas, which indicates the system is charged to possibly feed the next eruption.Dr Gottsmann said: "Our results indicate that localised extension along the fault zone controls the accumulation, ascent and eruption of magma at Ilopango. This fault-controlled magma accumulation and movement limits potential vent locations for future eruptions at the caldera in its central, western and northern part -- an area that now forms part of the metropolitan area of San Salvador, which is home to 2 million people. As a consequence, there is a significant level of risk to San Salvador from future eruptions of Ilopango." | Earthquakes | 2,016 |
July 21, 2016 | https://www.sciencedaily.com/releases/2016/07/160721144128.htm | Tide-triggered tremors give clues for earthquake prediction | The triggering of small, deep earthquakes along California's San Andreas Fault reveals depth-dependent frictional behavior that may provide insight into patterns signaling when a major quake could be on the horizon, according to a paper released this week by the | The study, which was led by the U.S. Geological Survey and Los Alamos National Laboratory, reports that the deepest part of California's 800-mile-long San Andreas Fault is weaker than expected and produces small earthquakes in response to tidal forces."These findings provide previously inaccessible information about the San Andreas Fault activity and strength," said Los Alamos National Laboratory's Paul Johnson, a coauthor on the paper and geophysicist in the Lab's Earth and Environmental Sciences Division. "The study's discovery of low-frequency-earthquake (LFE) and tidal triggering of the San Andreas Fault gives seismologists new warning signals and information about slightly more predictable triggers of quakes to come."Los Alamos maintains technical expertise in seismology and the behavior of Earth's crust as a part of its role monitoring underground nuclear testing globally and applies that expertise to other national challenges, including earthquakes.The team used a data set of 81,000 LFEs since 2008 to match LFEs to tides. They determined in addition to being modulated with the semidiurnal (twice daily) tides, LFEs are also modulated by fortnightly tides. The contrasting relationship between the LFE responses observed at two different tidal timescales should serve as a powerful constraint on understanding frictional behavior and stress transfer on the deep San Andreas."The findings provide new information regarding the fault zone structure with depth," Johnson said. The authors found that deep, small, low-frequency earthquakes (LFEs) on the San Andreas Fault are most likely to occur during the waxing period approaching a full or new moon within the fortnightly tide period of 14.7 days. The fortnightly tide modulates the semidiurnal (twice a day) tide. LFEs preferentially occur not when the tidal amplitude is highest, as might be expected, but when the tidal amplitude most exceeds its previous value, the authors found. LFEs correlate more strongly with larger-amplitude shear stress.Previous studies have found stronger tidal semidiurnal variation for deeper, continuously active LFE families. The team used two models to explain variations: One, based on friction studies, posited LFEs occur when stress accelerates slip. The other model suggests LFEs occur by simple threshold failure but are driven indirectly by tidally modulated creep. Regardless of which tidal triggering model is correct, the inverse relationship between the strength of the semidiurnal and fortnightly modulations provides a key insight into the mechanics of LFEs and the structure of the deep fault, according to the paper."The pattern of LFEs tells us something about loading rates and stress conditions in the deep part of the fault," said Andrew Delorey, a seismologist with Los Alamos. "We don't know to what extent the deep part of the fault where LFEs occur is coupled to the shallow part of the fault where regular earthquakes occur. We may find that as stress increases and approaches failure in the shallow fault, where large earthquakes occur, it will affect the pattern of LFEs in a way that allows us to use LFE behavior to infer conditions in the shallow fault."While tidal triggering of earthquakes is found only for select environments, triggering of tremor has been found almost everywhere that tectonic tremor is observed, generating insights into the mechanics of the brittle transition zones. The response to the tidal stress carries otherwise inaccessible information about fault strength and rheology. | Earthquakes | 2,016 |
July 19, 2016 | https://www.sciencedaily.com/releases/2016/07/160719110218.htm | Elderly Japanese most resilient in wake of triple disaster, study finds | Research into the aftermath of the Fukushima earthquake, tsunami and subsequent nuclear meltdown found that the oldest were least likely to experience a deterioration of existing chronic conditions. | The study also reveals that the health of people living in the countryside was more resilient than that of urban dwellers following the triple disaster of 2011.The findings are in contrast to previous studies that suggested that young, city-dwellers would be less susceptible to ill-health in the aftermath of a major disruptive event.Experts from the University of Edinburgh worked with Dr Masaharu Tsubokura from the University of Tokyo to track 400 diabetic patients who were treated by a public hospital in Minamisoma City, 23km away from the Fukushima nuclear power plant.They compared how well patients managed their blood sugar levels before the disaster in 2010 with how well they coped in the year following the earthquake.Two-thirds experienced a deterioration in their body's ability to regulate diabetes, with the number classed as having acute problems controlling blood sugar levels increasing from 32 per cent to 41 per cent.Age was the most significant factor in determining the level of robustness -- with each additional year providing more benefit.Evacuation did not protect patients from deteriorating health. A third of the patients studied left the area in the wake of the disaster. This group suffered an increased decline in its ability to control blood sugar, compared with those who remained.Sarah Hill, director of the University of Edinburgh's Global Public Health Unit, said: "We were incredibly surprised by these results, as they run counter to received wisdom about the impact of disasters on health."Younger, urban diabetics may have experienced greater stress as a result of the disaster causing greater disruption to their lives. Older patients may have been more content to stay put, meaning less upheaval and stress. The longevity of Japanese pensioners is well-known, so their healthy diet and lifestyle may also be a factor."The results will certainly help health professionals identify patients with chronic diseases who are most at risk in a disaster situation and ensure they get the appropriate help."The findings are from a paper, Sociodemographic patterning of long-term diabetes mellitus control following Japan's 3.11 triple disaster: A retrospective cohort study, published in the journal | Earthquakes | 2,016 |
July 18, 2016 | https://www.sciencedaily.com/releases/2016/07/160718142204.htm | Better understanding post-earthquake fault movement | Preparation and good timing enabled Gareth Funning and a team of researchers to collect a unique data set following the 2014 South Napa earthquake that showed different parts of the fault, sometimes only a few kilometers apart, moved at different speeds and at different times. | Aided by GPS measurements made just weeks before the earthquake and data from a new radar satellite, the team found post-earthquake fault movement, known as afterslip, was concentrated in areas of loosely packed sediment. Areas where the fault passed through bedrock tended to slip more during the actual earthquake.Sections of Highway 12, which runs through the earthquake zone, were broken during the initial 6.0 magnitude earthquake and were further damaged in the coming days due to afterslip. In some areas the afterslip damage exceeded the initial damage from the earthquake."No one has seen variability in afterslip like we saw," said Funning, an associate professor of earth sciences at the University of California, Riverside. "This helps us address a big question: Can we use geology as a proxy for fault behavior? Our findings suggest there is a relationship between those two things."The findings could have significant implications for earthquake hazard models, and also for planning earthquake response. If geological information can give a guide to the likely extent of future earthquakes, better forecasts of earthquake damage will be possible. And if areas likely to experience afterslip can be identified in advance, it can be taken into account when building or repairing infrastructure that crosses those faultsCalifornia, in particular the Hayward and Calaveras Faults, which run along the east side of the San Francisco Bay, seems more susceptible to afterslip than other earthquake-prone regions throughout the world, Funning said.The findings on the South Napa earthquake were recently published in paper, "Spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 South Napa, California, earthquake," in the journal Funning's work in the region just north of San Francisco dates back to 2006, when he was a post-doctoral researcher at UC Berkeley and noticed the area wasn't that well studied, at least compared to the central Bay Area.He continued the research after he was hired at UC Riverside and received funding from the United States Geological Survey to conduct surveys using GPS sensors in earthquake prone areas throughout Marin, Napa, Sonoma, Mendocino and Lake counties.He began the most recent survey in July 2014. When the South Napa earthquake struck on Aug. 24, 2014, he and three other researchers were in Upper Lake, CA in Lake County, about 70 miles north of the earthquake's epicenter, making additional measurements.The earthquake occurred at 3:20 a.m. By noon, Funning and the other researchers, Michael Floyd (a former post-doctoral researcher with Funning who is now a research scientist at the Massachusetts Institute of Technology), Jerlyn Swiatlowski (a graduate student working with Funning) and Kathryn Materna (a graduate student at UC Berkeley), had deployed additional GPS sensors in the earthquake zone in locations that they had, fortuitously, measured just seven weeks earlier.In total, there were more than 20 GPS sensors set up by Funning's team and scientists from the United States Geological Survey. They left the equipment out for four weeks following the earthquake.They then combined the GPS sensor data with remote sensing data. The South Napa earthquake was the first major earthquake to be imaged by Sentinel-1A, a European radar imaging satellite launched in 2014 that provides higher resolution information than was previously available. | Earthquakes | 2,016 |
July 14, 2016 | https://www.sciencedaily.com/releases/2016/07/160714151425.htm | Record-breaking volcanic kettle on Iceland explored | The Bárdarbunga eruption on Iceland has broken many records. The event in 2014 was the strongest in Europe since more than 240 years. The hole it left behind, the so-called caldera, is the biggest caldera formation ever observed. And the event as such was studied in unprecedented detail by a team of international scientists, amongst them a group from the GFZ German Research Centre for Geosciences. Together with lead author Magnus T. Gudmundsson from the University of Iceland, the team has now published its findings in the upcoming issue of | From August 2014 to February 2015, the Bárdabunga caldera was formed in the centre of Iceland. Calderas are kettle-shaped volcanic structures with a diameter of one kilometer up to 100 kilometers. They form through the collapse of subterranean magma reservoirs during volcanic eruptions. Since their formation is not very frequent, knowledge of such calderas is scarce. As part of an international team, GFZ scientists from the section Physics of Earthquakes and Volcanoes documented the event in great detail. The scientists used satellite images, seismological and geochemical data, GPS data and modelling.The process of subsidence was triggered by the lateral intrusion of magma from a reservoir 12 kilometers below the surface. The magma flowed for 45 kilometers along a subterranean path before erupting as a major lava flow northeast of the volcano. The subsidence was accompanied by 77 earthquakes reaching magnitudes larger than M 5.In their study, the scientists show how the ice-filled subsidence bowl developed gradually over the course of six months to become eight by eleven kilometers wide and up to 65 meters deep. "Dr. Sebastian Heimann (GFZ) investigated the mechanisms underlying the collapse using seismological methods. "Another surprise for the scientists was how the magma behaved within the canal beneath the surface. "The chamber lies beneath Europe's largest glacier, the Vatnajökull, and the caldera was filled with ice. Thomas Walter says: "With the data they gathered, the geoscientists hope to gain deeper insights into the currently un-explored mechanisms of caldera formation. Eruptions connected to such processes can be far bigger than the observed Icelandic event. Catastrophic events can occur for instance at Yellowstone, USA, or in the Andes region. Exactly 200 years ago, the eruption of the Tambora volcano in Indonesia and the subsequent caldera formation lead to an atmospheric shock wave that could be measured globally as well as to a devastating tsunami. The volcanic aerosols and ash in the stratosphere brought the infamous "year without summer" in 1816. | Earthquakes | 2,016 |
July 13, 2016 | https://www.sciencedaily.com/releases/2016/07/160713115102.htm | Earthquake prediction: An innovative technique for monitoring submarine faults | To monitor a segment of the North Anatolian seismic fault near Istanbul, an international team of researchers, in particular from CNRS and Université de Bretagne Occidentale, has installed a network of transponders on the floor of the Sea of Marmara. The aim is to measure motion of the sea floor on either side of this segment. The data collected during the first six months reveals that the fault is probably locked in the region of this segment, suggesting that there is a progressive build-up of energy that could be released suddenly. This could cause a major earthquake in the Istanbul area. | The study, carried out by a collaboration of researchers from France, Germany and Turkey, is published in The North Anatolian fault, which caused destructive earthquakes in Turkey in 1999, is comparable to the San Andreas fault in California. It marks the boundary between the Eurasian and Anatolian tectonic plates, which move relative to each other at a speed of around 2 cm per year. The behavior of one underwater segment of the fault, located a few tens of kilometers from Istanbul in the Sea of Marmara, particularly intrigues researchers, since there has apparently been no seismic activity there since the eighteenth century. How does this segment behave? Does it continuously creep? Does it regularly give way, occasionally causing small, low-magnitude quakes? Or is it locked, making it likely that it will one day rupture and cause a major earthquake?Observing the motion of a submarine fault in situ over a period of several years is no easy matter. To meet this challenge, the researchers are testing an innovative underwater remote sensing method, using active, autonomous acoustic transponders remotely accessible from the sea surface. Placed on the sea floor on either side of the fault at a depth of 800 meters, the transponders take it in turns to interrogate each other in pairs, and measure the round-trip time of an acoustic signal between them. These time lapses are then converted into distances between the transponders. The variation in these distances over time is used to detect motion of the sea floor and any deformation of the network of transponders, and thus infer the displacement of the fault. Specifically, a network of ten French and German transponders was set up during an initial sea cruise1 in October 2014. The first six months of data (travel time, temperature, pressure and stability)2 have confirmed that the system is performing well. Following calculations, the data show no significant motion of the monitored fault, within the network's resolution limits. The distances between the transponders, which are between 350 and 1700 meters apart, are measured with a resolution of 1.5 to 2.5 mm. The segment is therefore probably locked or nearly locked, and is accumulating stress that could trigger an earthquake. However, it will be necessary to acquire data for several years in order to confirm this observation or show that this part of the fault has a more complex behavior.Going beyond this specific demonstration, if this approach, known as acoustic seafloor geodesy, proves to be robust in the long term (in this case, three to five years are planned, within the limits of the autonomy of the batteries), it could be included within a permanent underwater observatory as an addition to other observations (seismology, gas bubble emission, etc) for in situ real-time monitoring of the activity of this particular fault, or of other active submarine faults elsewhere in the world.The work was carried out by the Laboratoire Domaines Océaniques3 (LDO, CNRS/Université de Bretagne Occidentale), in collaboration with the Laboratoire Littoral Environnement et Sociétés (CNRS/Université de La Rochelle), GEOMAR (Kiel, Germany), Centre Européen de Recherche et d'Enseignement de Géosciences de l'Environnement (CNRS/Collège de France/AMU/IRD), the IFREMER's Laboratoire Géosciences Marines, the Eurasian Institute of Earth Sciences at the Istanbul Technical University (Turkey), and the Kandilli Observatory and Earthquake Research Institute at Bogazici University, Istanbul. This paper is dedicated to the memory of the Principal Investigator of the project, Anne Deschamps, CNRS researcher at LDO, who passed away shortly after leading the successful deployment of the acoustic transponders.1. By the oceanographic vessel Pourquoi pas?, with the help of IFREMER's Laboratoire Géosciences Marines2. The data was collected from the surface during the campaign of the German oceanographic vessel Poseidon in April 2015.3. This laboratory is attached to the Institut Universitaire Européen de la Mer -- IUEM (CNRS/UBO/IRD) | Earthquakes | 2,016 |
July 11, 2016 | https://www.sciencedaily.com/releases/2016/07/160711151313.htm | A giant quake may lurk under Bangladesh and beyond | A huge earthquake may be building beneath Bangladesh, the most densely populated nation on earth. Scientists say they have new evidence of increasing strain there, where two tectonic plates underlie the world's largest river delta. They estimate that at least 140 million people in the region could be affected if the boundary ruptures; the destruction could come not only from the direct results of shaking, but changes in the courses of great rivers, and in the level of land already perilously close to sea level. | The newly identified threat is a subduction zone, where one section of earth's crust, or a tectonic plate, is slowly thrusting under another. All of earth's biggest known earthquakes occur along such zones; these include the Indian Ocean quake and tsunami that killed some 230,000 people in 2004, and the 2011 Tohoku quake and tsunami off Japan, which swept away more than 20,000 and caused the Fukushima nuclear disaster. Up to now, all known such zones were only under the ocean; this one appears to be entirely under the land, which greatly multiplies the threat. The findings appear in this week's issue of Subduction-zone quakes generally occur where plates of heavy ocean crust slowly dive offshore beneath the lighter rocks of adjoining continents, or under other parts of the seafloor. Sometimes sections get stuck against each other over years or centuries, and then finally slip, moving the earth. Scientists knew of the plate boundary in and around Bangladesh, but many assumed it to be sliding only horizontally near the surface, where it sometimes causes fairly large, but less damaging earthquakes in areas that are not as densely populated. However, the authors of the new research say movements on the surface over the past decade show that subduction is taking place below, and that part of the plate juncture is locked and loading up with stress. They are not forecasting an imminent great earthquake, but say it is an "underappreciated hazard.""Some of us have long suspected this hazard, but we didn't have the data and a model," said lead author Michael Steckler, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory. "Now we have the data and a model, and we can estimate the size." He said strain between the plates has been building for at least 400 years -- the span of reliable historical records, which lack reports of any mega-quake. When an inevitable release comes, the shaking is likely to be larger than 8.2, and could reach a magnitude of 9, similar to the largest known modern quakes, said Steckler. "We don't know how long it will take to build up steam, because we don't know how long it was since the last one," he said. We can't say it's imminent or another 500 years. But we can definitely see it building."The newly identified zone is an extension of the same tectonic boundary that caused the 2004 Indian Ocean undersea quake, some 1,300 miles south. As the boundary reaches southeast Asia, the complexity of the motions along it multiply, and scientists do not completely understand all of them. But basically, they say, a giant plate comprising India and much of the Indian Ocean has been thrusting northeasterly into Asia for tens of millions of years. This collision has caused the Himalayas to rise to the north, bringing events like the 2015 Nepal quake that killed 8,000 people. Bangladesh, India's neighbor, lies on the far eastern edge of this plate, but pressure from the collision seems to be warping Asia clockwise around the top of Bangladesh, ending up largely in the next country over, Myanmar. This wraparound arrangement has resulted in a crazy quilt of faults and quakes in and around Bangladesh. Among the largest, a 1762 subduction-zone quake near the southern coast killed at least 700 people. This January, a magnitude 6.7 event in adjoining eastern India killed more than 20. There have been dozens of large quakes in between, but the assumption was that no actual subduction was taking place under Bangladesh itself, seeming to insulate the region from a truly gigantic one. The new study undercuts this idea.Starting in 2003, U.S. and Bangladeshi researchers set up about two dozen ground-positioning (GPS) instruments linked to satellites, capable of tracking tiny ground motions. Ten years of data now show that eastern Bangladesh and a bit of eastern India are pushing diagonally into western Myanmar at a rapid clip -- 46 millimeters per year, or about 1.8 inches. Combined with existing GPS data from India and Myanmar, the measurements show that much of the resulting strain has been taken up by several known, slowly moving surface faults in Myanmar and India. But the rest of the movement -- about 17 millimeters, or two-thirds of an inch per year -- is shortening the distance from Myanmar to Bangladesh. This has been going on for a long time, and the results are clearly visible: neatly parallel north-south ranges of mountains draping the landscape, like a carpet being shoved against a wall. The researchers interpret the shortening pattern to mean that subduction is taking place below, and that a huge zone -- about 250 kilometers by 250 kilometers, more than 24,000 square miles -- is locked and building pressure, just a few miles below the surface. The zone includes Bangladesh's densely packed capital of Dhaka, a megalopolis of more than 15 million.Steckler says that, assuming fairly steady motion over the last 400 years, enough strain has built for the zone to jump horizontally by about 5.5 meters, or 18 feet, if the stress is released all at once. If strain has been building longer, it could be up to 30 meters, or almost 100 feet. The land would also move vertically, to a lesser extent. This is the worst-case scenario; in the best case, only part would slip, and the quake would be smaller and farther from Dhaka, said Steckler.In any case, Bangladesh and eastern India sit atop a landscape vulnerable even to moderate earthquakes: the vast delta of the Ganges and Brahmaputra rivers. This is basically a pile of mud as deep as 12 miles, washed from the Himalayas to the coast, covering the subduction zone. In a quake, this low-lying substrate would magnify the shaking like gelatin, and liquefy in many places, sucking in buildings, roads and people, said study coauthor Syed Humayun Akhter, a geologist at Dhaka University. The great rivers -- 10 miles across in places -- could jump their banks and switch course, drowning everything in the way; there is in fact evidence that such switches have happened in previous centuries.Akhter says that fast-growing, poor Bangladesh is unprepared; no building codes existed before 1993, and even now, shoddy new construction flouts regulations. Past quake damages and deaths are no indicator of what could happen now, he said; population and infrastructure have grown so fast that even fairly moderate events like those of past centuries could be mega-disasters. "Bangladesh is overpopulated everywhere," he said. "All the natural gas fields, heavy industries and electric power plants are located close to potential earthquakes, and they are likely to be destroyed. In Dhaka, the catastrophic picture will be beyond our imagination, and could even lead to abandonment of the city."Roger Bilham, a geophysicist at the University of Colorado who has studied the region but was not involved in the new paper, said its "data are unassailable, the interpretation is sound." Bilham said the research "ties an enormous amount of structural interaction together. We have seen in recent history only modest seismicity responding to those interactions. The Indian subcontinent is effectively being pushed into a tight corner."Susan Hough, a U.S. Geological Survey seismologist who also studies the region and was not involved in the study, said that in recent years, "we've been surprised by big earthquakes that have not been witnessed during historical times, or witnessed so long ago, they were forgotten. Studies like this are critical for identifying those zones."Scientists in Bangladesh and neighboring countries continue to assess the hazards. James Ni, a seismologist at New Mexico State University, said he and colleagues hope to deploy 70 seismometers across Myanmar in 2017, to get a better image of the apparently subducting slab. "We don't have a good idea of its geometry, we don't know how far it goes down," said Ni. He said that if the study authors are right, and the slab is building strain, a quake would probably turn urban areas in eastern India "into ruins," and effects likely would extend into Myanmar and beyond. "We need more data," he said.The other authors of the study are Dhiman Ranjan Mondal of the City University of New York; Leonardo Seeber, Jonathan Gale and Michael Howe of Lamont-Doherty Earth Observatory; and Lujia Feng and Emma Hill of Singapore's Nanyang Technological University. The research was supported by the U.S. National Science Foundation. | Earthquakes | 2,016 |
July 7, 2016 | https://www.sciencedaily.com/releases/2016/07/160707100807.htm | Understanding tsunamis with EM fields | Could electromagnetic fields be used in tsunami early warning? New research shows that important focal parameters of tsunamigenic earthquakes -- particularly fault dip direction -- can be extracted from tsunami-borne EM fields. | "It's been five years since we discovered that tsunamis generate EM fields," says Hiroaki Toh, who led the Kyoto University study. "We've now demonstrated that tsunami-generated EM fields are a reliable and useful source of information for seismology,"Tsunamis consist of large volumes of electrically conductive seawater, generating EM fields through the coupling of synchronous seawater motion with the Earth's geomagnetic field. In a previous study, Toh's team found that those tsunami-generated fields revealed information such as the height of the tsunami, its direction of travel, and its type (a rise wave or a backwash)."This time we aimed to extract information about hypocenters of tsunamigenic earthquakes," explains Toh.Knowing the direction in which the fault dips could be helpful for tsunami early warning, as the direction sometimes determines whether a rise wave or a backwash hits a particular costal area."With backwash, residents of coastal areas get more time to evacuate. The real disaster is when rise waves come in your direction; you can't afford to lose a single moment.""But fault dips are one of the most difficult characteristics to investigate. Even with modern techniques in seismology, seismic waves don't always tell us the direction in which the fault is dipping. In these instances, we have to wait for aftershocks to occur and make inferences from them."Toh and former graduate student Issei Kawashima analyzed waves from a 2007 tsunami earthquake at the Kuril Trench, off the northeast coast of Hokkaido. With improvements to preexisting methods in calculating tsunamis' phase velocity, they found that the fault dip lay to the southeast direction."EM fields have been measured on the ocean floor of the northwest Pacific since 2001," says Toh. "This research further proves that EM fields from tsunamis are rich in information that can eventually be applied to global tsunami early warning." | Earthquakes | 2,016 |
July 6, 2016 | https://www.sciencedaily.com/releases/2016/07/160706174225.htm | New study upends a theory of how Earth's mantle flows | A new study carried out on the floor of Pacific Ocean provides the most detailed view yet of how the earth's mantle flows beneath the ocean's tectonic plates. The findings, published in the journal | By developing a better picture of the underlying engine of plate tectonics, scientists hope to gain a better understanding of the mechanisms that drive plate movement and influence related process, including those involving earthquakes and volcanoes.When we look out at the earth, we see its rigid crust, a relatively thin layer of rock that makes up the continents and the ocean floor. The crust sits on tectonic plates that move slowly over time in a layer called the lithosphere. At the bottom of the plates, some 80 to 100 kilometers below the surface, the asthenosphere begins. Earth's interior flows more easily in the asthenosphere, and convection here is believed to help drive plate tectonics, but how exactly that happens and what the boundary between the lithosphere and asthenosphere looks like isn't clear.To take a closer look at these processes, a team led by scientists from Columbia University's Lamont-Doherty Earth Observatory installed an array of seismometers on the floor of the Pacific Ocean, near the center of the Pacific Plate. By recording seismic waves generated by earthquakes, they were able to look deep inside the earth and create images of the mantle's flow, similar to the way a doctor images a broken bone.Seismic waves move faster through flowing rock because the pressure deforms the crystals of olivine, a mineral common in the mantle, and stretches them in the same direction. By looking for faster seismic wave movement, scientists can map where the mantle is flowing today and where it has flowed in the past.Three basic forces are believed to drive oceanic plate movement: plates are "pushed" away from mid-ocean ridges as new sea floor forms; plates are "pulled" as the oldest parts of the plate dive back into the earth at subduction zones; and convection within the asthenosphere helps ferry the plates along. If the dominant flow in the asthenosphere resulted solely from "ridge push" or "plate pull," then the crystals just below the plate should align with the plate's movement. The study finds, however, that the direction of the crystals doesn't correlate with the apparent plate motion at any depth in the asthenosphere. Instead, the alignment of the crystals is strongest near the top of the lithosphere where new sea floor forms, weakest near the base of the plate, and then peaks in strength again about 250 kilometers below the surface, deep in the asthenosphere."If the main flow were the mantle being sheared by the plate above it, where the plate is just dragging everything with it, we would predict a fast direction that's different than what we see," said coauthor James Gaherty, a geophysicist at Lamont-Doherty. "Our data suggest that there are two other processes in the mantle that are stronger: one, the asthenosphere is clearly flowing on its own, but it's deeper and smaller scale; and, two, seafloor spreading at the ridge produces a very strong lithospheric fabric that cannot be ignored." Shearing probably does happen at the plate boundary, Gaherty said, but it is substantially weaker.Donald Forsyth, a marine geophysicist at Brown University who was not involved in the new study, said, "These new results will force reconsideration of prevailing models of flow in the oceanic mantle."Looking at the entire upper mantle, the scientists found that the most powerful process causing rocks to flow happens in the upper part of the lithosphere as new sea floor is created at a mid-ocean ridge. As molten rock rises, only a fraction of the flowing rock squeezes up to the ridge. On either side, the pressure bends the excess rock 90 degrees so it pushes into the lithosphere parallel to the bottom of the crust. The flow solidifies as it cools, creating a record of sea floor spreading over millions of years.This "corner flow" process was known, but the study brings it into greater focus, showing that it deforms the rock crystals to a depth of at least 50 kilometers into the lithosphere.In the asthenosphere, the patterns suggest two potential flow scenarios, both providing evidence of convection channels that bottom out about 250 to 300 kilometers below the earth's surface. In one scenario, differences in pressure drive the flow like squeezing toothpaste from a tube, causing rocks to flow east-to-west or west-to-east within the channel. The pressure difference could be caused by hot, partially molten rock piled up beneath mid-ocean ridges or beneath the cooling plates diving into the earth at subduction zones, the authors write. Another possible scenario is that small-scale convection is taking place within the channel as chunks of mantle cool and sink. High-resolution gravity measurements show changes over relatively small distances that could reflect small-scale convection."The fact that we observe smaller-scale processes that dominate upper-mantle deformation, that's a big step forward. But it still leaves uncertain what those flow processes are. We need a wider set of observations from other regions," Gaherty said.The study is part of the NoMelt project, which was designed to explore the lithosphere-asthenosphere boundary at the center of an oceanic plate, far from the influence of melting at the ridge. The scientists believe the findings here are representative of the Pacific Basin and likely ocean basins around the world.NoMelt is unique because of its location. Most studies use land-based seismometers at edge of the ocean that tend to highlight the motion of the plates over the asthenosphere because of its large scale and miss the smaller-scale processes. NoMelt's ocean bottom seismometer array, with the assistance of Lamont's seismic research ship the Marcus G. Langseth, recorded data from earthquakes and other seismic sources from the middle of the plate over the span of a year. | Earthquakes | 2,016 |
July 6, 2016 | https://www.sciencedaily.com/releases/2016/07/160706114615.htm | Penguin colonies at risk from erupting volcano | A volcano erupting on a small island in the Sub Antarctic is depositing ash over one of the world's largest penguin colonies. | Zavodovski Island is a small island in the South Sandwich archipelago and its volcano Mt Curry has been erupting since March 2016. The island is home to over one million chinstrap penguins -- the largest colony for this species in the world.The island is part of the British Overseas Territory of South Georgia & the South Sandwich Islands and uninhabited. British Antarctic Survey (BAS) recently remapped this chain of volcanic islands and was alerted to a large (7.2) magnitude earthquake last month in the vicinity.Researchers confirmed from satellite imagery that not one, but two volcanoes are erupting in the South Sandwich Islands. Mt Curry on Zavodovski Island to the north of the archipelago and Mt Sourabaya on Bristol Island to the south.Following the earthquake, fishing vessels in the area licenced by the Government of South Georgia & the South Sandwich Islands, captured photos of the Zavodovski Island eruption. They show the main volcanic vent is on the western side of the island, but the prevailing wind is blowing the smoke and ash to the east, and depositing much of it on the lower slopes of the volcano. These are home to the chinstraps, closely packed in great numbers. In addition there are around 180,000 macaroni penguins.Satellite images have confirmed that between one third and one half of the island has so far been covered in ash. At the time photos were taken, the adult chinstraps were moulting, shedding their old feathers for new ones and therefore unable to leave the island.Geographer Dr Peter Fretwell from BAS who was involved in the remapping of the archipelago says:"We don't know what impact the ash will have on the penguins. If it has been heavy and widespread it may have a serious effect on the population. It's impossible to say but two scientific expeditions are scheduled to visit the region from later this year and will try to assess the impact of the eruption."Penguin ecologist Mike Dunn from BAS says, "As the images were captured during the moult period for the chinstraps, the consequences could be very significant. When the penguins return to breed later in the year, it will be interesting to see what impact this event has on their numbers." | Earthquakes | 2,016 |
June 30, 2016 | https://www.sciencedaily.com/releases/2016/06/160630214454.htm | Fukushima and the oceans: What do we know, five years on? | A major international review of the state of the oceans 5 years after the Fukushima disaster shows that radiation levels are decreasing rapidly except in the harbour area close to the nuclear plant itself where ongoing releases remain a concern. At the same time, the review's lead author expresses concern at the lack of ongoing support to continue the radiation assessment, which he says is vital to understand how the risks are changing. | These are the conclusions of a major 5 year review, with multi-international authors who are all working together as part of a Scientific Committee on Oceanic Research (SCOR) Working Group. The report is being presented at the Goldschmidt geochemistry conference in Japan. The review paper is also published in Lead author, Dr. Ken Buesseler (Woods Hole Oceanographic Institution, USA) said: "This report pulls together much of the academic, industry and government studies to form a more complete picture of the amount of radioactivity released, its fate and transport in the ocean, whether we should be worried or not, and what can be predicted for the future. Overall, the results show a trend of decreasing radiation risk in oceans themselves and to marine life. This is generally true, except for the harbour at Fukushima NPP. The highest remaining oceanic contamination remains in seafloor sediments off coast of Japan.Despite this, we are still concerned that there is little support to continue assessments as time goes by, in particular from the US federal agencies which have not supported any ocean studies. This is not good, as public concern is ongoing, and we can learn a lot even when levels go down in the environment, and are no longer of immediate health concern."Prof. Bernd Grambow, Director of SUBATECH laboratory, Nantes, France and leader of the research group on interfacial reaction field chemistry of the ASRC/JAEA, Tokai, Japan, commented: "This report is an excellent summary of the impact and the fate of the release of radioactive substances to the ocean. While the distribution and impact of radioactive material becomes clearer with time, a lot of work still needs to be done. Discharge flux rates of Cs-137 to the ocean continue to be in the range of some TBq/yr. Forest and soil bound Cs-137 is only slowly being washed away, with waste piles accumulating in many placesThe evolution of transfer mechanisms and the flux of radioactive material through soils, plants and food chain from land to ocean are still insufficiently understood and still deserve close attention of the international scientific community." | Earthquakes | 2,016 |
June 29, 2016 | https://www.sciencedaily.com/releases/2016/06/160629135238.htm | Plate tectonics without jerking: Detailed recordings of earthquakes on ultraslow mid-ocean ridges | The earthquake distribution on ultraslow mid-ocean ridges differs fundamentally from other spreading zones. Water circulating at a depth of up to 15 kilometres leads to the formation of rock that resembles soft soap. This is how the continental plates on ultraslow mid-ocean ridges may move without jerking, while the same process in other regions leads to many minor earthquakes, according to geophysicists of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). Their study is going to be published advanced online in the journal | Mountain ranges like the Himalayas rise up where continental plates collide. Mid-ocean ridges, where the continents drift apart, are just as spectacular mountain ranges, but they are hidden in the depths of the oceans. On the seabed, like on a conveyor belt, new ocean floor (oceanic lithosphere) is formed as magma rises from greater depths to the top, thus filling the resulting gap between the lithospheric plates. This spreading process creates jerks, and small earthquakes continuously occur along the conveyor belt. The earthquakes reveal a great deal about the origin and structure of the new oceanic lithosphere. On the so-called ultraslow ridges, the lithospheric plates drift apart so slowly that the conveyor belt jerks and stutters and, because of the low temperature, there is insufficient melt to fill the gap between the plates. This way, the earth's mantle is conveyed to the seabed in many places without earth crust developing. In other locations along this ridge, on the other hand, you find giant volcanoes.Ultraslow ridges can be found under the sea ice in the Arctic and south of Africa along the Southwest Indian Ridge in the notorious sea areas of the Roaring Forties and Furious Fifties. Because these areas are so difficult to access, earthquakes have not been measured there. And so until now, little was known about the structure and development of around 20 percent of the global seabed.With the research vessel Polarstern, a reliable workhorse even in heavy seas, the researchers around Dr Vera Schlindwein of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have now for the first time risked deploying a network of ocean bottom seismometers (OBS) at the Southwest Indian Ridge in the Furious Fifties and recovered them a year later. At the same time, a second network was placed on a volcano in the more temperate latitudes of the Southwest Indian Ridge. "Our effort and our risk were rewarded with a unique set of earthquake data, which for the first time provides deep insights into the formation of the ocean floor when spreading rates are very slow," explains AWI geophysicist Vera Schlindwein.Her results turn current scientific findings on the functioning of ultra-slow mid-ocean ridges upside down: Schlindwein and her PhD student Florian Schmid found that water may circulate up to 15 kilometres deep in the young oceanic lithosphere, i.e. the earth crust and the outer part of the earth mantle. If this water comes into contact with rock from the earth mantle, a greenish rock called serpentinite forms. Even small quantities of ten percent serpentinite are enough for the rock to move without any earthquakes as if on a soapy track. The researchers discovered such aseismic areas, clearly confined by many small earthquakes, in their data.Until now, scientists thought that serpentinite only forms near fault zones and near the surface. "Our data now suggest that water circulates through extensive areas of the young oceanic lithosphere and is bound in the rock. This releases heat and methane, for example, to a degree not previously foreseen," says Vera Schlindwein.The AWI geophysicists were now able to directly observe the active spreading processes using the ocean floor seismometers, comparing volcanic and non-volcanic ridge sections. "Based on the distribution of earthquakes, we are for the first time able to watch, so to speak, as new lithosphere forms with very slow spreading rates. We have not had such a data set from ultra-slow ridges before," says Vera Schlindwein."Initially, we were very surprised that areas without earth crust show no earthquakes at all down to 15 kilometres depth, even though OBS were positioned directly above. At greater depths and in the adjacent volcanic areas, on the other hand, where you can find basalt on the sea floor and a thin earth crust is present, there were flurries of quakes in all depth ranges," says Vera Schlindwein about her first glance at the data after retrieving the OBS with RV Polarstern in 2014.The results also have an influence on other marine research disciplines: geologists think about other deformation mechanisms of the young oceanic lithosphere. Because rock that behaves like soft soap permits a completely different deformation, which could be the basis of the so-called "smooth seafloor" that is only known from ultra-slow ridges. Oceanographers are interested in heat influx and trace gases in the water column in such areas, which were previously thought to be non-volcanic and "cold." Biologists are interested in the increased outflow of methane and sulphide on the sea floor that is to be expected in many areas and that represents an important basis of life for deep-sea organisms. | Earthquakes | 2,016 |
June 24, 2016 | https://www.sciencedaily.com/releases/2016/06/160624155000.htm | Giant blobs of rock, deep inside the earth, hold important clues about our planet | Two massive blob-like structures lie deep within Earth, roughly on opposite sides of the planet. The two structures, each the size of a continent and 100 times taller than Mount Everest, sit on the core, 1,800 miles deep, and about halfway to the center of Earth. | Arizona State University scientists Edward Garnero, Allen McNamara and Sang-Heon (Dan) Shim, of the School of Earth and Space Exploration, suggest these blobs are made of something different from the rest of Earth's mantle. The scientists' work appears in the June issue of "While the origin and composition of the blobs are yet unknown," said Garnero, "we suspect they hold important clues as to how Earth was formed and how it works today."The blobs, he says, may also help explain the plumbing that leads to some massive volcanic eruptions, as well as the mechanism of plate tectonics from the convection, or stirring, of the mantle. This is the geo-force that drives earthquakes.Earth is layered like an onion, with a thin outer crust, a thick viscous mantle, a fluid outer core and a solid inner core. The two blobs sit in the mantle on top of Earth's core, under the Pacific Ocean on one side and beneath Africa and the Atlantic Ocean on the other.Waves from earthquakes passing through Earth's deep interior have revealed that these blobs are regions where seismic waves travel slowly. The mantle materials that surround these regions are thought to be composed of cooler rocks, associated with the downward movement of tectonic plates.The blobs, also called thermochemical piles, have long been depicted as warmer-than-average mantle materials, pushed upward by a slow churning of hot mantle rock. The new paper argues they are also chemically different from the surrounding mantle rock, and may partly contain material pushed down by plate tectonics. They might even be material left over from Earth's formation, 4.5 billion years ago.Much is yet to be learned about these blobs. But the emerging view from seismic and geodynamic information is that they appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and have been shaped by the mantle's large-scale flow. The scientists expect that further work on the two deep-seated anomalies will help clarify the picture and tell of their origin."If a neuroscientist found an unknown structure in the human brain, the whole community of brain scientists, from psychologists to surgeons, would actively pursue understanding its role in the function of the whole system," Garnero said."As the thermochemical piles come into sharper focus, we hope other Earth scientists will explore how these features fit into the big puzzle of planet Earth." | Earthquakes | 2,016 |
June 20, 2016 | https://www.sciencedaily.com/releases/2016/06/160620120250.htm | New analysis reveals large-scale motion around San Andreas Fault System | An array of GPS instruments near the San Andreas Fault System in Southern California detects constant motion of Earth's crust--sometimes large, sudden motion during an earthquake and often subtle, creeping motion. By carefully analyzing the data recorded by the EarthScope Plate Boundary Observatory's GPS array researchers from the University of Hawai'i at Mānoa (UHM), University of Washington and Scripps Institution of Oceanography (SIO) discovered nearly 125 mile-wide "lobes" of uplift and subsidence--a few millimeters of motion each year--straddling the fault system. This large scale motion was previously predicted in models but until now had not been documented. | The GPS array records vertical and horizontal motion of Earth's surface. Vertical motion is affected by many factors including tectonic motion of the crust, pumping of groundwater, local surface geology, and precipitation. The challenge faced by Samuel Howell, doctoral candidate at the UHM School of Ocean and Earth Science and Technology (SOEST) and lead author of the study, and co-authors was to discern the broad, regional tectonic motion from the shorter-scale, local motion.To tease out such motions, the team used a comprehensive statistical technique to extract from the GPS data a pattern of large-scale, smoothly varying vertical motions of the local crust."While the San Andreas GPS data has been publicly available for more than a decade, the vertical component of the measurements had largely been ignored in tectonic investigations because of difficulties in interpreting the noisy data. Using this technique, we were able to break down the noisy signals to isolate a simple vertical motion pattern that curiously straddled the San Andreas fault," said Howell.The pattern resulting from their data analysis was similar in magnitude and direction to motions predicted by previously published earthquake cycle model results led by co-authors Bridget Smith-Konter, associate professor at UHM SOEST, and David Sandwell, professor at SIO."We were surprised and thrilled when this statistical method produced a coherent velocity field similar to the one predicted by our physical earthquake cycle models," said Smith-Konter. "The powerful combination of a priori model predictions and a unique analysis of vertical GPS data led us to confirm that the buildup of century-long earthquake cycle forces within the crust are a dominant source of the observed vertical motion signal."The new findings, published today in | Earthquakes | 2,016 |
June 14, 2016 | https://www.sciencedaily.com/releases/2016/06/160614133623.htm | Researcher helps break ground on forecasting earthquakes | A University of Montana researcher is part of a team whose research is breaking ground on the complexity of earthquakes and the possibility to forecast them. | Rebecca Bendick, who works in UM's Department of Geosciences, used GPS records of surface motion to map the 7.8 magnitude Gorkha earthquake, which broke a 150-kilometer section of the Himalayas in April 2015, terminating close to Kathmandu."Measuring this earthquake tells us that the past history of great Himalayan earthquakes is much more complicated than previously thought," Bendick said.The Gorkha earthquake failed to rupture the Himalayan faults all the way to the surface. But rapid initial afterslip occurred north of the earthquake under Tibet during the first six months following the quake, releasing aseismic-moment equivalent to a magnitude 7.1 earthquake.Similar "incomplete" historical earthquakes have occurred in the Himalayas in 1803, 1833, 1905 and 1947.Bendick said this study shows rather than just rare and extremely large quakes doing all the work, a mixture of smaller and larger quakes cause the Himalayas to edge over India."This means our ability to forecast earthquake hazards in the region is even worse than we thought," she said. "The most important and practical message is that residents of the region should be prepared for more frequent, but perhaps less catastrophic quakes."The area just west of the Gorkha quake, spanning western Nepal and the Indian Himalaya has a very high earthquake hazard, Bendick said, with potential for either a large quake or megaquake."The pervasive lack of information transfer from earthquake research to people living in zones of high earthquake hazard has led to hundreds of thousands of fatalities in the past decade, a crisis unlikely to change in the future unless basic earthquake literacy is provided to those at risk," Bendick said. | Earthquakes | 2,016 |
June 13, 2016 | https://www.sciencedaily.com/releases/2016/06/160613153408.htm | Arc volcano releases mix of material from Earth's mantle and crust | Volcanoes are an explosive and mysterious process by which molten rock from Earth's interior escapes back into the atmosphere. Why the volcano erupts -- and where it draws its lava from -- could help trace the lifecycle of materials that make up our planet. | New University of Washington research shows that a common type of volcano is not just spewing molten rock from the mantle, but contains elements that suggest something more complicated is drawing material out of the descending plate of Earth's crust.Geologists have long believed that solidified volcanic lava, or basalt, originates in the mantle, the molten rock just below the crust. But the new study uses detailed chemical analysis to find that the basalt's magnesium -- a shiny gray element that makes up about 40 percent of the mantle but is rare in the crust -- does not look like that of the mantle, and shows a surprisingly large contribution from the crust. The paper was published the week of June 13 in the "Although the volcanic basalt was produced from the mantle, its magnesium signature is very similar to the crustal material," said lead author Fang-Zhen Teng, a UW associate professor of Earth and space sciences. "The ocean-floor basalts are uniform in the type of magnesium they contain, and other geologists agree that on a global scale the mantle is uniform," he said. "But now we found one type of the mantle is not."The study used rock samples from an inactive volcano on the Caribbean island of Martinique, a region where an ocean plate is slowly plunging, or subducting, beneath a continental plate. This situation creates an arc volcano, a common type of volcano that includes those along the Pacific Ocean's "Ring of Fire."Researchers chose to study a volcano in the Caribbean partly because the Amazon River carries so much sediment from the rainforest to the seabed. One reason scientists want to pin down the makeup of volcanic material is to learn how much of the carbon-rich sediment from the surface gets carried deep in the Earth, and how much gets scraped off from the descending plate and reemerges into the planet's atmosphere.Analyzing the weight of magnesium atoms in the erupted basalt shows that they came not from the mantle, nor from the organic sediment scraped off during the slide, but directly from the descending oceanic crust. Yet the volcanic basalt lacks other components of the crust."The majority of the other ingredients are still like the mantle; the only difference is the magnesium. The question is: Why?" Teng said.The authors hypothesize that at great depths, magnesium-rich water is squeezed from the rock that makes up Earth's crust. As the fluid travels, the surrounding rock acts like a Brita filter that picks up the magnesium, transferring magnesium particles from the crust to the mantle just below the subduction zone."This is what we think is very exciting," Teng said. "Most people think you add either crustal or mantle materials as a solid. Here we think the magnesium was added by a fluid."Fluids seem to play a role in seismic activity at subduction zones, Teng said, and having more clues to how those fluids travel deep in the Earth could help better understand processes such as volcanism and deep earthquakes.He and co-author Yan Hu, a UW doctoral student in Earth and space sciences, plan to do follow-up studies on basalt rocks from the Cascade Mountains and other arc volcanoes to analyze their magnesium composition and see if this effect is widespread.The other co-author is Catherine Chauvel at the University of Grenoble in France. The research was funded by the U.S. National Science Foundation and the French National Research Agency. | Earthquakes | 2,016 |
June 13, 2016 | https://www.sciencedaily.com/releases/2016/06/160613131100.htm | Electrical conductivity of salt water in seismogenic zones theoretically determined | A joint research team consisting of Hiroshi Sakuma, senior researcher, Functional Geomaterials Group, Environment and Energy Materials Division, National Institute for Materials Science (NIMS), Japan, and Masahiro Ichiki, assistant professor, Graduate School of Science, Tohoku University, Japan, succeeded in theoretically determining the electrical conductivity of NaCl solution (salt water) in a high-temperature and high-pressure environment at ground depths ranging from 10 to 70 km. By comparison with electrical conductivity data collected underground, the theoretical approach indicated the presence of salt water deep underground. This discovery may reinforce the theory that underground salt water influences the occurrence of earthquakes and volcanic eruptions. | It is commonly said that the presence of salt water in bedrock makes a fault prone to slide, influencing the occurrence of earthquakes, or decreases the melting points of rocks, influencing volcanic eruptions.However, it is difficult to directly verify the presence of salt water through drilling surveys deep underground. Since liquids including salt water have electrical conductivity about six orders of magnitude higher than that of solids, surveys involving the measurement of electrical conductivity are often carried out to detect the presence of salt water. However, because the electrical conductivity of salt water under the high-temperature and high-pressure conditions occurring in such environments as crustal seismogenic zones is unknown, it had been impossible to associate electrical conductivity measurements with the presence of salt water.The research team developed a molecular model to reproduce the supercritical state of water. Using the model, the team successfully calculated electrical conductivity of salt water with NaCl concentrations ranging from one-sixth to triple that in seawater at high temperature and high pressure (temperature: 673-2,000 K, pressure: 0.2-2 GPa), conditions that are difficult to simulate in experiments. These electrical conductivity data indicated that high electrical conductivity measured under the ground in the Tohoku region may be explained by the presence of salt water with salt concentrations equivalent to seawater.In future studies, we will combine these results with the electromagnetic crustal observations across Japan to identify the presence of salt water deep underground where seismic and volcanic activities are high, as in subduction zones, and conduct research in order to understand the mechanism of the outbreak of earthquakes and volcanic eruption.This research was conducted as a part of the projects "Geofluids: nature and dynamics of fluids in subduction zones," (Grant-in-Aid for Scientific Research on New Academic Related Areas) and "Research on understanding supercritical fluid properties in crust through molecular dynamics calculation and its influence on earthquake occurrence," (Grant-in-Aid for Challenging Exploratory Research) supported by the Ministry of Education, Culture, Sports, Science and Technology.This research was published in the online version of Journal of Geophysical Research: Solid Earth, on January 20, 2016. | Earthquakes | 2,016 |
June 13, 2016 | https://www.sciencedaily.com/releases/2016/06/160613122233.htm | Mounting tension in the Himalaya | The Gorkha earthquake struck Nepal on April 25, 2015. It's a part of the world that is prone to earthquakes, as the Indian plate makes its incremental, sticky descent beneath the Eurasian plate. The magnitude 7.8 jolt, which was very shallow (only 15 km underground), caused a tremendous amount of damage in Kathmandu. But it didn't rupture the Earth's surface, signifying that only part of the fault had slipped, below-ground. | In the following days, even the afterslip--post-earthquake movement--produced little surface evidence of continued movement. That meant only one of two things could be happening: either the part of the fault that hadn't moved was experiencing a slow-slip event, a slow-motion earthquake, or it remained completely locked, accumulating further strain in that segment of the fault. A new research paper, out online from David Mencin, the lead author on that paper, is a graduate student with CIRES and the University of Colorado Boulder's Department of Geological Sciences and a project manager with the geoscience non-profit UNAVCO. Following the earthquake, an international team of scientists quickly deployed a series of GPS receivers to monitor any movements. They also relied on InSAR--interferometric synthetic aperture radar--to look for changes to the Earth's surface. They found there had been 70 mm (2.75 inches) of afterslip north of the rupture and about 25 mm (1 inch) of afterslip to the south of the rupture. But scientists estimate there's about 3.5 meters (11.5 feet) worth of strain built into this fault, which those post-earthquake movements did nothing to alleviate."There was a clear lack of afterslip," says Mencin. "That has implications for future great earthquakes, which can tap into this stored strain."CIRES Fellow Roger Bilham, a co-author on the study and Professor of Geological Sciences, got an early look at the fault zone when he took a helicopter flight over the area following the quake."Roger went out there immediately to search for a surface rupture," says Mencin. "A newly formed 3.5 meter escarpment (upthrust) would have been obvious, even to the casual tourist."Historical earthquakes in the region--in 1803, 1833, 1905 and 1947--also failed to rupture the surface of the Himalayan frontal faults and they, too, experienced a lack of afterslip or large subsequent earthquakes. That, according to the team's research, means there's significant strain throughout the region."There's no evidence that it will spontaneously rupture in another damaging earthquake," says Bilham. "But the strain may fuel a future earthquake starting nearby. The entire Himalayan arc may host dozens of pockets of strain energy awaiting release in future great earthquakes."And this region remains vulnerable to earthquakes, not only because of its geography, but because of its architecture and development patterns. While this 2015 earthquake killed 8,000 people, left tens of thousands homeless and destroyed parts of Kathmandu, the amount of strain built up in the faults, if released suddenly, could do much more damage in this part of the world. That's why Mencin and his colleagues are already at work on their next paper, which they hope might help identify patterns across the entire Himalayan front."We're trying to understand the earthquake cycle in the Himalaya and understand how they happen," says Mencin. | Earthquakes | 2,016 |
June 10, 2016 | https://www.sciencedaily.com/releases/2016/06/160610094437.htm | Deep 'scars' from ancient geological events play role in current earthquakes | Super-computer modelling of Earth's crust and upper-mantle suggests that ancient geologic events may have left deep 'scars' that can come to life to play a role in earthquakes, mountain formation, and other ongoing processes on our planet. | This changes the widespread view that only interactions at the boundaries between continent-sized tectonic plates could be responsible for such events.A team of researchers from the University of Toronto and the University of Aberdeen have created models indicating that former plate boundaries may stay hidden deep beneath the Earth's surface. These multi-million-year-old structures, situated at sites away from existing plate boundaries, may trigger changes in the structure and properties at the surface in the interior regions of continents."This is a potentially major revision to the fundamental idea of plate tectonics," says lead author Philip Heron, a postdoctoral fellow in Russell Pysklywec's research group in U of T's Department of Earth Sciences. Their paper, "Lasting mantle scars lead to perennial plate tectonics," appears in the June 10, 2016 edition of Heron and Pysklywec, together with University of Aberdeen geologist Randell Stephenson have even proposed a 'perennial plate tectonic map' of the Earth to help illustrate how ancient processes may have present-day implications."It's based on the familiar global tectonic map that is taught starting in elementary school," says Pysklywec, who is also chair of U of T's Department of Earth Sciences. "What our models redefine and show on the map are dormant, hidden, ancient plate boundaries that could also be enduring or "perennial" sites of past and active plate tectonic activity."To demonstrate the dominating effects that anomalies below the Earth's crust can have on shallow geological features, the researchers used U of T's SciNet -- home to Canada's most powerful computer and one of the most powerful in the world- to make numerical models of the crust and upper-mantle into which they could introduce these scar-like anomalies.The team essentially created an evolving "virtual Earth" to explore how such geodynamic models develop under different conditions."For these sorts of simulations, you need to go to a pretty high-resolution to understand what's going on beneath the surface," says Heron. "We modeled 1,500 kilometres across and 600 kilometres deep, but some parts of these structures could be just two or three kilometres wide. It is important to accurately resolve the smaller-scale stresses and strains."Using these models, the team found that different parts of the mantle below the Earth's crust may control the folding, breaking, or flowing of the Earth's crust within plates -- in the form of mountain-building and seismic activity -- when under compression.In this way, the mantle structures dominate over shallower structures in the crust that had previously been seen as the main cause of such deformation within plates."The mantle is like the thermal engine of the planet and the crust is an eggshell above," says Pysklywec. "We're looking at the enigmatic and largely unexplored realm in the Earth where these two regions meet.""Most of the really big plate tectonic activity happens on the plate boundaries, like when India rammed into Asia to create the Himalayas or how the Atlantic opened to split North America from Europe," says Heron. "But there are lots of things we couldn't explain, like seismic activity and mountain-building away from plate boundaries in continent interiors."The research team believes their simulations show that these mantle anomalies are generated through ancient plate tectonic processes, such as the closing of ancient oceans, and can remain hidden at sites away from normal plate boundaries until reactivation generates tectonic folding, breaking, or flowing in plate interiors."Future exploration of what lies in the mantle beneath the crust may lead to further such discoveries on how our planet works, generating a greater understanding of how the past may affect our geologic future," says Heron.The research carries on the legacy of J. Tuzo Wilson, also a U of T scientist, and a legendary figure in geosciences who pioneered the idea of plate tectonics in the 1960's."Plate tectonics is really the cornerstone of all geoscience," says Pysklywec. "Ultimately, this information could even lead to ways to help better predict how and when earthquakes happen. It's a key building block." | Earthquakes | 2,016 |
May 24, 2016 | https://www.sciencedaily.com/releases/2016/05/160524213456.htm | A warning system for tsunamis | Seismologists have created a new algorithm that could one day help give coastal cities early warning of incoming tsunamis. | Right now, tsunami warning systems rely on region-specific scenarios based on previous patterns in that area. That's because scientists use sensors in the ocean, which can detect abnormal movements but can't make accurate projections of how much water will hit a coast and how hard. But "most likely" isn't a sure thing. If a real tsunami doesn't match any of the known scenarios, it could result in significant loss of life.Scientists at the Australian National University developed the Time Reverse Imaging Method to take real-time data from the ocean sensors and use that information to recreate what the tsunami looked like when it was born. Once scientists have the tsunami source pinpointed, they can use it to make better predictions about what will happen once the waves reach shore. This new method is fast enough to compete with existing algorithms but much more accurate."[The Time Reverse Imaging Method] is not based on some guess, it's based on [real-time] information," said Jan Dettmer, a seismologist at the university. "[This method] would improve accuracy without sacrificing speed."Dettmer and his colleagues will speak about their tsunami-tracking algorithm at the 171st meeting of the Acoustical Society of America, held May 23-27 in Salt Lake City.The researchers studied plate tectonics in the Japan Trench to help create the algorithm. The earth's crust is broken up into large plates that float on top of the mantle, which is part of the earth's core. These plates move and push against each other, ultimately creating deep trenches and high mountains over the course of millennia.When the movement happens very quickly, it's an earthquake. Earthquakes can cause landmasses to move several meters, and if it happens underwater it creates a tsunami. Tsunamis kill an average of 8,000 people every year, according to the United Nations Office for Disaster Risk Reduction. That's why early warning is so important."Once the earthquake happens, then we have minutes," Dettner said. Dettmer's system takes scientists one step closer to accurately predicting a tsunami's trajectory. In order to predict its course, you need know the initial sea surface displacement, or, what the wave looked like when it first started.That's difficult to do because, while the Japanese government has placed a lot of sensors in the Pacific Ocean, they do not cover the entire seafloor. So Dettmer looked at the information gathered from the March 11, 2011, Tohoku-Oki earthquake and tsunami.Dettmer took the information from the 2011 event and used it to go backward in time mathematically, calculating what the tsunami looked like when it first started. Once he had the information from the beginning of the tsunami, he added it to the sensor data and projected what the tsunami would look like once it hit land.By checking his results against what actually happened in 2011, Dettmer was able to hone his algorithm.The plan is to apply test his method on other recorded earthquakes and fine-tune the technology until it is ready for implementation, which he says could be in less than five years."This is a step forward," Dettmer adds. "This research can be part of the next generation of tsunami warning systems that are based on real time information." | Earthquakes | 2,016 |
May 18, 2016 | https://www.sciencedaily.com/releases/2016/05/160518133832.htm | New study finds major earthquake threat from the Riasi fault in the Himalayas | New geologic mapping in the Himalayan mountains of Kashmir between Pakistan and India suggests that the region is ripe for a major earthquake that could endanger the lives of as many as a million people. | Scientists have known about the Riasi fault in Indian Kashmir, but it wasn't thought to be as much as a threat as other, more active fault systems. However, following a magnitude 7.6 earthquake in 2005 on the nearby Balakot-Bagh fault in the Pakistan side of Kashmir -- which was not considered particularly dangerous because it wasn't on the plate boundary -- researchers began scrutinizing other fault systems in the region.What they found is that the Riasi fault has been building up pressure for some time, suggesting that when it does release or "slip," the resulting earthquake may be large -- as much as magnitude 8.0 or greater.Results of the new study, which was funded by the National Science Foundation, have been accepted for publication by the "What we set out to learn was how much the fault has moved in the last tens of thousands of years, when it moved, and how different segments of the fault move," said Yann Gavillot, lead author on the study who did much of the work as a doctoral student at Oregon State University. "What we found was that the Riasi fault is one of the main active faults in Kashmir, but there is a lack of earthquakes in the more recent geologic record."The fault hasn't slipped for a long time, which means the potential for a large earthquake is strong. It's not a question of if it's going to happen. It's a matter of when."There is direct evidence of some seismic activity on the fault, where the researchers could see displacement of Earth where an earthquake lifted one section of the fault five or more meters -- possibly about 4,000 years ago. Written records from local monasteries refer to strong ground-shaking over the past several thousand years.But the researchers don't have much evidence as to how frequent major earthquakes occur on the fault, or when it may happen again."The Riasi fault isn't prominent on hazard maps for earthquake activity, but those maps are usually based more on the history of seismic activity rather than the potential for future events," said Andrew Meigs, a geology professor in OSU's College of Earth, Ocean, and Atmospheric Sciences and co-author on the study. "In actuality, the lack of major earthquakes heightens the likelihood that seismic risk is high."The researchers say 50 percent of the seismic "budget" for the fault can be accounted for with the new information. The budget is determined over geologic time by the movement of the tectonic plates. In that region, the India tectonic plate is being subducted beneath the Asia plate at a rate of 14 millimeters a year; the Riasi fault accounts for half of that but has no records of major earthquakes since about 4,000 years ago, indicating a major slip, and earthquake, is due."In the last 4,000 years, there has only been one major event on the Riasi fault, so there is considerable slip deficit," Meigs said. "When there is a long gap in earthquakes, they have the potential to be bigger unless earthquakes on other faults release the pressure valve. We haven't seen that. By comparison, there have been about 16 earthquakes in the past 4,000 years in the Cascadia Subduction Zone off the Northwest coast of the United States."Gavillot said a major earthquake at the Riasi fault could have a major impact on Jammu, the Indian capital of the Indian state of Jammu and Kashmir, which has a population of about 1.5 million people. Another 700,000 people live in towns located right on the fault."There are also several dams on the Chenab River near the fault, and a major railroad that goes through or over dozens of tunnels, overpasses and bridges," Gavillot said. "The potential for destruction is much greater than the 2005 earthquake."The 2005 Kashmir earthquake killed about 80,000 people in Pakistan and India. | Earthquakes | 2,016 |
May 17, 2016 | https://www.sciencedaily.com/releases/2016/05/160517130758.htm | Humans have been causing earthquakes in Texas since the 1920s | Earthquakes triggered by human activity have been happening in Texas since at least 1925, and they have been widespread throughout the state ever since, according to a new historical review of the evidence published online May 18 in | The earthquakes are caused by oil and gas operations, but the specific production techniques behind these quakes have differed over the decades, according to Cliff Frohlich, the study's lead author and senior research scientist and associate director at the Institute for Geophysics at the University of Texas at Austin.Frohlich said the evidence presented in the SRL paper should lay to rest the idea that there is no substantial proof for human-caused earthquakes in Texas, as some state officials have claimed as recently as 2015.At the same time, Frohlich said, the study doesn't single out any one or two industry practices that could be managed or avoided to stop these kinds of earthquakes from occurring. "I think we were all looking for what I call the silver bullet, supposing we can find out what kinds of practices were causing the induced earthquakes, to advise companies or regulators," he notes. "But that silver bullet isn't here."The researchers write that since 2008, the rate of Texas earthquakes greater than magnitude 3 has increased from about two per year to 12 per year. This change appears to stem from an increase in earthquakes occurring within 1-3 kilometers of petroleum production wastewater disposal wells where water is injected at a high monthly rate, they note.Some of these more recent earthquakes include the Dallas-Fort Worth International Airport sequence between 2008 and 2013; the May 2012 Timpson earthquake; and the earthquake sequence near Azle that began in 2013.Frohlich and his colleagues suspected that induced seismicity might have a lengthy and geographically widespread history in Texas. "But for me, the surprise was that oil field practices have changed so much over the years, and that probably affects the kinds of earthquakes that were happening at each time," Frohlich said.In the 1920s and 1930s, for instance, "they'd find an oilfield, and hundreds of wells would be drilled, and they'd suck oil out of the ground as fast as they could, and there would be slumps" that shook the earth as the volume of oil underground was rapidly extracted, he said.When those fields were mostly depleted, in the 1940s through the 1970s, petroleum operations "started being more aggressive about trying to drive oil by water flooding" and the huge amounts of water pumped into the ground contributed to seismic activity, said Frohlich.In the past decade, enhanced oil and gas recovery methods have produced considerable amounts of wastewater that is disposed by injection back into the ground through special wells, triggering nearby earthquakes. Most earthquakes linked to this type of wastewater disposal in Texas are smaller (less than magnitude 3) than those in Oklahoma, the study concludes.The difference may lie in the types of oil operations in each state, Frohlich said. The northeast Texas injection earthquakes occur near high-injection rate wells that dispose of water produced in hydrofracturing operations, while much of the Oklahoma wastewater is produced during conventional oil production and injected deep into the underlying sedimentary rock.For the moment, there have been no magnitude 3 or larger Texas earthquakes that can be linked directly to the specific process of hydrofracturing or fracking itself, such as have been felt in Canada, the scientists concluded.Frohlich and colleagues used a five-question test to identify induced earthquakes in the Texas historical records. The questions cover how close in time and space earthquakes and petroleum operations are, whether the earthquake center is at a relatively shallow depth (indicating a human rather than natural trigger); whether there are known or suspected faults nearby that might support an earthquake or ease the way for fluid movement, and whether published scientific reports support a human cause for the earthquake.In 2015, the Texas legislature funded a program that would install 22 additional seismic monitoring stations to add to the state's existing 17 permanent stations, with the hopes of building out a statewide monitoring network that could provide more consistent and objective data on induced earthquakes. | Earthquakes | 2,016 |
May 16, 2016 | https://www.sciencedaily.com/releases/2016/05/160516095132.htm | Clues to ancient giant asteroid found in Australia | Scientists have found evidence of a huge asteroid that struck the Earth early in its life with an impact larger than anything humans have experienced. | Tiny glass beads called spherules, found in north-western Australia were formed from vaporised material from the asteroid impact, said Dr Andrew Glikson from The Australian National University (ANU)."The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble," said Dr Glikson, from the ANU Planetary Institute."Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago."The asteroid is the second oldest known to have hit the Earth and one of the largest.Dr Glikson said the asteroid would have been 20 to 30 kilometres across and would have created a crater hundreds of kilometres wide.About 3.8 to 3.9 billion years ago the moon was struck by numerous asteroids, which formed the craters, called mare, that are still visible from Earth"Exactly where this asteroid struck the earth remains a mystery," Dr Glikson said."Any craters from this time on Earth's surface have been obliterated by volcanic activity and tectonic movements."Dr Glikson and Dr Arthur Hickman from Geological Survey of Western Australia found the glass beads in a drill core from Marble Bar, in north-western Australia, in some of the oldest known sediments on Earth.The sediment layer, which was originally on the ocean floor, was preserved between two volcanic layers, which enabled very precise dating of its origin.Dr Glikson has been searching for evidence of ancient impacts for more than 20 years and immediately suspected the glass beads originated from an asteroid strike.Subsequent testing found the levels of elements such as platinum, nickel and chromium matched those in asteroids.There may have been many more similar impacts, for which the evidence has not been found, said Dr Glikson."This is just the tip of the iceberg. We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds""Asteroid strikes this big result in major tectonic shifts and extensive magma flows. They could have significantly affected the way the Earth evolved."The research is published in the journal | Earthquakes | 2,016 |
May 13, 2016 | https://www.sciencedaily.com/releases/2016/05/160513100854.htm | New research estimates probability of mega-earthquake in the Aleutians | A team of researchers from the University of Hawai'i at Mānoa (UHM) published a study this week that estimated the probability of a Magnitude 9+ earthquake in the Aleutian Islands--an event with sufficient power to create a mega-tsunami especially threatening to Hawai'i. In the next 50 years, they report, there is a 9% chance of such an event. An earlier State of Hawai'i report has estimated the damage from such an event would be nearly $40 billion, with more than 300,000 people affected. | Earth's crust is composed of numerous rocky plates. An earthquake occurs when two sections of crust suddenly slip past one another. The surface where they slip is called the fault, and the system of faults comprises a subduction zone. Hawai'i is especially vulnerable to a tsunami created by an earthquake in the subduction zone of the Aleutian Islands."Necessity is the mother of invention," said Rhett Butler, lead author and geophysicist at the UHM School of Ocean and Earth Science and Technology (SOEST). "Having no recorded history of mega tsunamis in Hawai'i, and given the tsunami threat to Hawai'i, we devised a model for Magnitude 9 earthquake rates following upon the insightful work of David Burbidge and others."Butler and co-authors Neil Frazer (UHM SOEST) and William Templeton (now at Portland State University) created a numerical model based only upon the basics of plate tectonics: fault length and plate convergence rate, handling uncertainties in the data with Bayesian techniques.To validate this model, the researchers utilized recorded histories and seismic/tsunami evidence related to the 5 largest earthquakes (greater than Magnitude 9) since 1900 (Tohoku, 2011; Sumatra-Andaman, 2004; Alaska, 1964; Chile, 1960; and Kamchatka, 1952)."These five events represent half of the seismic energy that has been released globally since 1900," said Butler. "The events differed in details, but all of them generated great tsunamis that caused enormous destruction."To further refine the probability estimates, they took into account past (prior to recorded history) tsunamis--evidence of which is preserved in geological layers in coastal sediments, volcanic tephras, and archeological sites."We were surprised and pleased to see how well the model actually fit the paleotsunami data," said Butler.Using the probability of occurrence, the researchers were able to annualize the risk. They report the chance of a Magnitude 9 earthquake in the greater Aleutians is 9% ± 3% in the next 50 years. Hence the risk is 9% of $40 billion, or $3.6 billion. Annualized, this risk is about $72 million per year. Considering a worst-case location for Hawai'i limited to the Eastern Aleutian Islands, the chances are about 3.5% in the next 50 years, or about $30 million annualized risk. In making decisions regarding mitigation against this $30-$72 million risk, the state can now prioritize this hazard with other threats and needs.The team is now considering ways to extend the analysis to smaller earthquakes, Magnitude 7-8, around the Pacific. | Earthquakes | 2,016 |
May 9, 2016 | https://www.sciencedaily.com/releases/2016/05/160509115116.htm | Map of flow within the Earth's mantle finds the surface moving up and down 'like a yo-yo' | Researchers have compiled the first global set of observations of the movement of the Earth's mantle, the 3000-kilometre-thick layer of hot silicate rocks between the crust and the core, and have found that it looks very different to predictions made by geologists over the past 30 years. | The team, from the University of Cambridge, used more than 2000 measurements taken from the world's oceans in order to peer beneath the Earth's crust and observe the chaotic nature of mantle flow, which forces the surface above it up and down. These movements have a huge influence on the way that the Earth looks today -- the circulation causes the formation of mountains, volcanism and other seismic activity in locations that lie in the middle of tectonic plates, such as at Hawaii and in parts of the United States.They found that the wave-like movements of the mantle are occurring at a rate that is an order of magnitude faster than had been previously predicted. The results, reported in the journal "Although we're talking about timescales that seem incredibly long to you or me, in geological terms, the Earth's surface bobs up and down like a yo-yo," said Dr Mark Hoggard of Cambridge's Department of Earth Sciences, the paper's lead author. "Over a period of a million years, which is our standard unit of measurement, the movement of the mantle can cause the surface to move up and down by hundreds of metres."Besides geologists, the movement of the Earth's mantle is of interest to the oil and gas sector, since these motions also affect the rate at which sediment is shifted around and hydrocarbons are generated.Most of us are familiar with the concept of plate tectonics, where the movement of the rigid plates on which the continents sit creates earthquakes and volcanoes near their boundaries. The flow of the mantle acts in addition to these plate motions, as convection currents inside the mantle -- similar to those at work in a pan of boiling water -- push the surface up or down. For example, although the Hawaiian Islands lie in the middle of a tectonic plate, their volcanic activity is due not to the movement of the plates, but instead to the upward flow of the mantle beneath."We've never been able to accurately measure these movements before -- geologists have essentially had to guess what they look like," said Hoggard. "Over the past three decades, scientists had predicted that the movements caused continental-scale features which moved very slowly, but that's not the case."The inventory of more than 2000 spot observations was determined by analysing seismic surveys of the world's oceans. By examining variations in the depth of the ocean floor, the researchers were able to construct a global database of the mantle's movements.They found that the mantle convects in a chaotic fashion, but with length scales on the order of 1000 kilometres, instead of the 10,000 kilometres that had been predicted."These results will have wider reaching implications, such as how we map the circulation of the world's oceans in the past, which are affected by how quickly the sea floor is moving up and down and blocking the path of water currents," said Hoggard. "Considering that the surface is moving much faster than we had previously thought, it could also affect things like the stability of the ice caps and help us to understand past climate change." | Earthquakes | 2,016 |
May 6, 2016 | https://www.sciencedaily.com/releases/2016/05/160506160115.htm | Scientists track Greenland's ice melt with seismic waves | Researchers from MIT, Princeton University, and elsewhere have developed a new technique to monitor the seasonal changes in Greenland's ice sheet, using seismic vibrations generated by crashing ocean waves. The results, which will be published in the journal | "One of the major contributors to sea level rise will be changes to the ice sheets," says Germán Prieto, the Cecil and Ida Green Career Development Assistant Professor in the Department of Earth, Atmospheric and Planetary Sciences (EAPS) at MIT. "With our technique, we can continuously monitor ice sheet volume changes associated with winter and summer. That's something that global models need to be able to take into account when calculating how much ice will contribute to sea level rise."Prieto and his colleagues study the effects of "seismic noise," such as ocean waves, on Earth's crust. As ocean waves crash against the coastline, they continuously create tiny vibrations, or seismic waves."They happen 24 hours a day, seven days a week, and they generate a very small signal, which we generally don't feel," Prieto says. "But very precise seismic sensors can feel these waves everywhere in the world. Even in the middle of continents, you can see these ocean effects."The seismic waves generated by ocean waves can propagate through Earth's crust, at speeds that depend in part on the crust's porosity: The more porous the rocks, the slower seismic waves travel. The scientists reasoned that any substantial overlying mass, such as an ice sheet, may act like a weight on a sponge, squeezing the pores closed or letting them reopen, depending on whether the ice above is shrinking or growing in size.The team, led by Aurélien Mordret, a postdoc in EAPS, hypothesized that the speed of seismic waves through Earth's crust may therefore reflect the volume of ice lying above."By looking at velocity changes, we can make predictions of the volume change of the ice sheet mass," Prieto says. "We can do this continuously over time, day by day, for a particular region where you have seismic data being recorded."Scientists typically track changing ice sheets using laser altimetry, in which an airplane flies over a region and sends a laser pulse down and back to measure an ice sheet's topography. Researchers can also look to data gathered by NASA's GRACE (Gravity Recovery and Climate Experiment) mission -- twin satellites that orbit Earth, measuring its gravity field, from which scientists can infer an ice sheet's volume.As Prieto points out, "you can only do laser altimetry several times a year, and GRACE satellites require about one month to cover Earth's surface."In contrast, ocean waves and the seismic waves they produce generate signals that sensors can pick up continuously."This has very good time resolution, so it can look at melting over short time periods, like summer to winter, with really high precision that other techniques might not have," Prieto says.The researchers looked through seismic data collected from January 2012 to January 2014, from a small seismic sensor network situated on the western side of Greenland's ice sheet. The sensors record seismic vibrations generated by ocean waves along the coast, and they have been used to monitor glaciers and earthquakes. Prieto's team is the first to use seismic data to monitor the ice sheet itself.Looking through the seismic data, the scientists were able to detect incredibly small changes in the velocity of seismic waves, of less than 1 percent. They tracked average velocities from January 2012 to 2014, and observed very large seismic velocity decreases in 2012, versus 2013. These measurements mirrored the observations of ice sheet volume made by the GRACE satellites, which recorded abnormally large melting in 2012 versus 2013. The comparison suggested that seismic data may indeed reflect changes in ice sheets.Using data from the GRACE satellites, the team then developed a model to predict the volume of the ice sheet, given the velocity of the seismic waves within Earth's crust. The model's predictions matched the satellite data with 91 percent accuracy.Toward that end, the team plans next to use available seismic networks to track the seasonal changes in the Antarctic ice sheet."Our efforts right now are to use what's available," Prieto says. "Nobody has been looking at this particular area using seismic data to monitor ice sheet volume changes."If the technique is proven reliable in Antarctica, Prieto hopes to stimulate a large-scale project involving many more seismic sensors distributed along the coasts of Greenland and Antarctica."If you have very good coverage, like an array with separations of about 70 kilometers, we could in principle make a map of the regions that have more melting than others, using this monitoring, and maybe better refine models of how ice sheets respond to climate change," Prieto says. | Earthquakes | 2,016 |
May 6, 2016 | https://www.sciencedaily.com/releases/2016/05/160506100415.htm | Seismic response of fiber-reinforced concrete coupled walls | To protect the lives of inhabitants, buildings are designed to sway and deform without collapsing in response to earthquake shaking. Many building owners and occupants also expect that, with a modest level of repair, buildings will be usable after a strong earthquake. To achieve these objectives, engineers take great care when designing and detailing structures located in regions of high seismic hazard. | Unfortunately, to ensure that structures have the desired deformation capacity, a large amount of specially detailed reinforcing steel is often required. In certain cases, the reinforcing steel that is required can be difficult and time-consuming to assemble, resulting in greater cost and duration of construction.What if there was a better way? What if a structure could be constructed in less time and at lower cost, but still exhibit the same deformation capacity? Furthermore, what if this structure tended to exhibit less damage after an earthquake than is typical of current construction?Researchers at the University of Michigan and the University of Wisconsin-Madison have been evaluating whether these goals can be achieved through the use of fiber reinforced concrete in earthquake-resistant construction.Fiber reinforced concrete (FRC) refers to concrete that has short fibers mixed evenly throughout the material. The research team used 1.2 in. long steel fibers with a 0.02 in. diameter made out of a high-strength steel wire. The fibers were mixed into the fresh concrete before it was poured into the formwork. These short fibers, which disburse randomly throughout the mixture, act like distributed reinforcement that holds the concrete together after it has cracked.The research team focused on studying the use of FRC in walls and coupling beams (coupling beams are used by engineers to link adjacent walls together and thereby stiffen tall structures). Isolated walls and coupled walls are commonly used in medium- and high-rise buildings located where there is a high seismic hazard. Construction of coupled wall systems can be difficult because of the need for a large amount of reinforcing steel that can be difficult to construct due to interference issues.Tests were conducted on large-scale specimens to evaluate the performance of walls constructed in a manner consistent with current practice and walls constructed with FRC. The specimens were built to approximately 1/3 of full-scale and then subjected to reversing lateral displacements to simulate earthquake loading.Results from this research showed that when walls and coupling beams are constructed with the FRC used in this project, reinforcing steel can be reduced significantly in the walls and coupling beams (by up to 40% in coupling beams) without compromising behavior. The FRC members had the same or better deformation capacity and showed less damage after testing than the members constructed without FRC.It therefore seems plausible that use of FRC in construction will allow for the use of less and simpler steel reinforcement while maintaining good structural behavior and potentially reducing the amount of post-earthquake repair. Such results will lead to a cheaper way to construct safe buildings with reduced life-cycle costs for the owner.This research can be found in a paper with the title "Seismic Response of Fiber-Reinforced Concrete Coupled Walls," published in the May-June edition of the | Earthquakes | 2,016 |
May 5, 2016 | https://www.sciencedaily.com/releases/2016/05/160505144723.htm | Tsunami risk: World's shallowest slow-motion earthquakes detected offshore of New Zealand | Research published in the May 6 edition of | "These data have revealed the true extent of slow-motion earthquakes at an offshore subduction zone for the first time," said Laura Wallace, a research scientist at The University of Texas at Austin's Institute for Geophysics who led the study.An international team of researchers from the U.S., Japan and New Zealand collaborated on the research. The Institute for Geophysics is a research unit of The University of Texas Jackson School of Geosciences.The world's most devastating tsunamis are generated by earthquakes that occur near the trenches of subduction zones, places where one tectonic plate begins to dive or "subduct" beneath another. Using a network of highly sensitive seafloor pressure recorders, the team detected a slow-slip event in September 2014 off the east coast of New Zealand. The study was undertaken at the Hikurangi subduction zone, where the Pacific Plate subducts beneath New Zealand's North Island.The slow-slip event lasted two weeks, resulting in 15-20 centimeters of movement along the fault that lies between New Zealand and the Pacific Plate, a distance equivalent to three to four years of background plate motion. If the movement had occurred suddenly, rather than slowly, it would have resulted in a magnitude 6.8 earthquake. The seafloor sensors recorded up to 5.5 centimeters of upward movement of the seafloor during the event.Slow-slip events are similar to earthquakes, but instead of releasing strain between two tectonic plates in seconds, they do it over days to weeks, creating quiet, centimeter-sized shifts in the landscape. In a few cases, these small shifts have been associated with setting off destructive earthquakes, such as the magnitude 9.0 Tohoku-Oki earthquake that occurred off the coast of Japan in 2011 and generated a tsunami that caused the Fukushima Daiichi nuclear power plant disaster.The slow-slip event that the team studied occurred in the same location as a magnitude 7.2 earthquake in 1947 that generated a large tsunami. The finding increases the understanding of the relationship between slow slip and normal earthquakes by showing that the two types of seismic events can occur on the same part of a plate boundary.The link has been difficult to document in the past because most slow-slip monitoring networks are land-based and are located far from the trenches that host tsunami-generating earthquakes, Wallace said. The data for this study was recorded by HOBITSS, a temporary underwater network that monitored slow-slip events by recording vertical movement of the seafloor. HOBITSS stands for "Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip.""Our results clearly show that shallow, slow-slip event source areas are also capable of hosting seismic rupture and generating tsunamis," said Yoshihiro Ito, a professor at Kyoto University and study co-author. "This increases the need to continuously monitor shallow, offshore slow-slip events at subduction zones, using permanent monitoring networks similar to those that have been established offshore of Japan."Professor Spahr Webb, a co-author from Columbia University's Lamont-Doherty Earth Observatory agreed."Our New Zealand experiment results demonstrate the great potential for using offshore monitoring systems at subduction zones in the Pacific Northwest for tsunami and earthquake early warning," said Webb.Earthquakes are unpredictable events, Wallace said, but the linkage between slow-slip events and earthquakes could eventually help in forecasting the likelihood of damaging earthquakes."To do that we will have to understand the links between slow-slip events and earthquakes much better than we currently do," Wallace said.The research team installed the HOBITSS network in May 2014, which consisted of 24 seafloor pressure gauges, and 15 ocean bottom seismometers. The team collected the devices and data in June 2015."The project findings add to critical information for anticipating potentially life-threatening earthquakes and tsunamis," said Maurice Tivey, program director of the National Science Foundation's Division of Ocean Sciences.Additional participants included scientists from the University of Tokyo, Tohoku University, GNS Science, the University of California at Santa Cruz and the University of Colorado Boulder.The research was funded by the National Science Foundation; the Japan Society for Promotion of Science; Japan's Ministry of Education, Culture, Sports, Science and Technology; and grants from participating universities and research institutions. | Earthquakes | 2,016 |
May 3, 2016 | https://www.sciencedaily.com/releases/2016/05/160503130840.htm | Likely cause for recent southeast US earthquakes: Underside of the North American Plate peeling off | The southeastern United States should, by all means, be relatively quiet in terms of seismic activity. It's located in the interior of the North American Plate, far away from plate boundaries where earthquakes usually occur. But the area has seen some notable seismic events -- most recently, the 2011 magnitude-5.8 earthquake near Mineral, Virginia that shook the nation's capital. | Now scientists report in a new study a likely explanation for this unusual activity: pieces of the mantle under this region have been periodically breaking off and sinking down into the Earth. This thins and weakens the remaining plate, making it more prone to slipping that causes earthquakes. The study authors conclude this process is ongoing and likely to produce more earthquakes in the future."Our idea supports the view that this seismicity will continue due to unbalanced stresses in the plate," said Berk Biryol, a seismologist at the University of North Carolina at Chapel Hill and lead author of the new study. "The [seismic] zones that are active will continue to be active for some time." The study was published today in the Compared to earthquakes near plate boundaries, earthquakes in the middle of plates are not well understood and the hazards they pose are difficult to quantify. The new findings could help scientists better understand the dangers these earthquakes present.Tectonic plates are composed of Earth's crust and the uppermost portion of the mantle. Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.Earthquakes typically occur at the boundaries of tectonic plates, where one plate dips below another, thrusts another upward, or where plate edges scrape alongside each other. Earthquakes rarely occur in the middle of plates, but they can happen when ancient faults or rifts far below the surface reactivate. These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.Today, the southeastern U.S. is more than 1,056 miles from the nearest edge of the North American Plate, which covers all of North America, Greenland and parts of the Atlantic and Arctic oceans. But the region was built over the past billion years by periods of accretion, when new material is added to a plate, and rifting, when plates split apart. Biryol and colleagues suspected ancient fault lines or pieces of old plates extending deep in the mantle following episodes of accretion and rifting could be responsible for earthquakes in the area."This region has not been active for a long time," Biryol said. "We were intrigued by what was going on and how we can link these activities to structures in deeper parts of the Earth."To find out what was happening deep below the surface, the researchers created 3D images of the mantle portion of the North American Plate. Just as doctors image internal organs by tracing the paths of x-rays through human bodies, seismologists image the interior of the Earth by tracing the paths of seismic waves created by earthquakes as they move through the ground. These waves travel faster through colder, stiffer, denser rocks and slower through warmer, more elastic rocks. Rocks cool and harden as they age, so the faster seismic waves travel, the older the rocks.The researchers used tremors caused by earthquakes more than 2,200 miles away to create a 3D map of the mantle underlying the U.S. east of the Mississippi River and south of the Ohio River. They found plate thickness in the southeast U.S. to be fairly uneven -- they saw thick areas of dense, older rock stretching downward and thin areas of less dense, younger rock."This was an interesting finding because everybody thought that this is a stable region, and we would expect regular plate thickness," Biryol said.At first, they thought the thick, old rocks could be remnants of ancient tectonic plates. But the shapes and locations of the thick and thin regions suggested a different explanation: through past rifting and accretion, areas of the North American Plate have become more dense and were pulled downward into the mantle through gravity. At certain times, the densest parts broke off from the plate and sank into the warm asthenosphere below. The asthenosphere, being lighter and more buoyant, surged in to fill the void created by the missing pieces of mantle, eventually cooling to become the thin, young rock in the images.The researchers concluded this process is likely what causes earthquakes in this otherwise stable region: when the pieces of the mantle break off, the plate above them becomes thinner and more prone to slip along ancient fault lines. Typically, the thicker the plate, the stronger it is, and the less likely to produce earthquakes.According to Biryol, pieces of the mantle have most likely been breaking off from underneath the plate since at least 65 million years ago. Because the researchers found fragments of hard rocks at shallow depths, this process is still ongoing and likely to continue into the future, potentially leading to more earthquakes in the region, he said. | Earthquakes | 2,016 |
April 28, 2016 | https://www.sciencedaily.com/releases/2016/04/160428132122.htm | Speedy bridge repair | In just 30 seconds, a devastating earthquake like the ones that struck Japan and Ecuador can render a city helpless. With roadways split and bridges severely damaged, residents and emergency personnel could be prevented from moving around to rebuild. | Normally, it takes weeks to repair the cracking or spalling of columns on just one bridge damaged in an earthquake. But a team of researchers led by University of Utah civil and environmental engineering professor Chris Pantelides has developed a new process of fixing columns that takes as little as a few days. This process is outlined in a new paper published April 28, 2016 in the most recent issue of the "With this design and process, it is much easier and faster for engineers and crews to rebuild a city ravaged by an earthquake so that critical roadways remain open for emergency vehicles," Pantelides says.In an earthquake, a bridge is designed to take the brunt of the damage at the top and bottom of the vertical columns where they meet the foundation and the horizontal beams. If a bridge survives from collapsing but the columns are damaged, it is likely too unstable to be driven over. And if several of the steel rebar in the columns have snapped, the bridge likely cannot be repaired at all and must be torn down.But if the columns can be repaired, engineers typically chip away at the concrete, replace any bent rebar and steel hoops inside and then pour new concrete into a steel cast that's built around the column. That's a lengthy process that leaves the bridge unusable for weeks until the repair is finished.Pantelides' quicker and more cost-effective process involves creating concrete donuts known as "repairs" that are lined with a composite fiber material built around the bottom and top of each column. The material is a carbon fiber-reinforced polymer made of fibers and resin that is stronger than concrete and steel.First, a number of steel rebars with heads are drilled into the foundation around the column and secured with an epoxy. Then two halves of a circular shell made of the composite fiber (that are just millimeters thick) are placed around the column and rebar and spliced together. Concrete is poured around the column and over the rebar with the composite fiber acting as a mold. The result is a repaired column with approximately the same structural integrity as the original column, Pantelides says."The circular shape gives you the best strength for the amount of material you are using. The stresses are distributed equally all around the periphery," he says. "With this method, if there are future earthquakes or aftershocks the bridge will survive and damage will happen adjacent to the donut. This gives the bridge a second life."The process also could be used to retrofit bridges to make them more earthquake-safe, though it was specifically designed for repair. And it's not limited to repairing just bridges. The procedure also can be used on damaged columns around a building. Pantelides and his team have filed patents on the process, and he says it can be utilized by construction companies on earthquake-ravaged areas immediately. | Earthquakes | 2,016 |
April 27, 2016 | https://www.sciencedaily.com/releases/2016/04/160427094859.htm | Rainwater may play an important role in process that triggers earthquakes | It's the rain's Fault | Rainwater may play an important role in the process that triggers earthquakes, according to new research.Researchers from the University of Southampton, GNS Science (New Zealand), the University of Otago, and GFZ Potsdam (Germany), identified the sources and fluxes of the geothermal fluids and mineral veins from the Southern Alps of New Zealand where the Pacific and Australian Plates collide along the Alpine Fault.From careful chemical analyses, they discovered that fluids originating from the mantle, the layer below Earth's crust, and fluids derived from rainwater, are channelled up the Alpine Fault.By calculating how much fluid is flowing through the fault zone at depth, the researchers showed for the first time that enough rainwater is present to promote earthquake rupture on this major plate boundary fault.Lead researcher Dr Catriona Menzies, from Ocean and Earth Science at the University of Southampton, said: "Large, continental-scale faults can cause catastrophic earthquakes, but the trigger mechanisms for major seismic events are not well known. Geologists have long suspected that deep groundwaters may be important for the initiation of earthquakes as these fluids can weaken the fault zones by increasing pressures or through chemical reactions."Fluids are important in controlling the evolution of faults between earthquake ruptures. Chemical reactions may alter the strength and permeability of rocks, and if enough fluid is present at sufficiently high pressures they may aid earthquake rupture by 'pumping up' the fault zone."The Alpine Fault is a major strike-slip fault, like the San Andreas, that fails in very large (Magnitude 8+) earthquakes around every 300 years. It last ruptured in 1717 AD and consequently it is under intense scientific scrutiny because it is a rare example of a major fault that is late in the strain-build up before rupture.Dr Menzies said: "We show that the Alpine Fault acts as a barrier to lateral fluid flow from the high mountains of the Southern Alps towards the Tasman Sea in the west. However, the presence of mantle-derived fluids indicates that the fault also acts as a channel for fluids, from more than 35 km depth, to ascend to the surface."As well as mantle derived fluids, our calculations indicate that 0.02-0.05 per cent of surface rainfall reaches around six kilometres depth but this is enough to overwhelm contributions from the mantle and fluids generated during mountain-building by metamorphic reactions in hot rocks. This rainwater is then focused onto the fault, forced by the hydraulic head of the high mountains above and the sub-vertical fluid flow barrier of the Alpine Fault."Funding for this research, published in | Earthquakes | 2,016 |
April 26, 2016 | https://www.sciencedaily.com/releases/2016/04/160426162613.htm | Chile quake at epicenter of expanding disaster, failure data repository | Feb. 27, 2010, is a date that most Chileans will probably never forget. On that day, the sixth strongest earthquake in recorded history--packing a force greater than the most powerful thermonuclear device ever tested--occurred off the country's central coast. Now, thanks to a newly available set of data collected in the aftermath of the disaster, the National Institute of Standards and Technology (NIST) is providing Chile and other quake-prone areas worldwide with a powerful tool toward becoming more resilient to future seismic events. | The massive shockwaves and accompanying tsunami of the 2010 Maule, Chile, earthquake (magnitude 8.8) killed more than 300 people, affected nearly 2 million others, and damaged or destroyed approximately half a million homes, schools, hospitals and other buildings. Following the event, an interdisciplinary team of researchers, including a NIST engineer, documented the devastation and chronicled the response of hundreds of structures. The comprehensive collection of this valuable information is now accessible as the newest addition to the NIST Disaster and Failure Studies Data Repository.The repository was established in 2011 to provide a place where data collected during and after a major disaster or structural failure, as well as data generated from related research, could be organized and maintained to facilitate study, analysis and comparison with future events. Eventually, NIST hopes that the repository will serve as a national archival database where other organizations can store the research, findings and outcomes of their disaster and failure studies.Initially, the NIST Disaster and Failure Studies Data Repository was established to house data from the agency's six-year investigation of the collapses of three buildings at New York City's World Trade Center (WTC 1, 2 and 7) as a result of the terrorist attacks on Sept. 11, 2001. With the addition of the 2010 Chile earthquake dataset, NIST is broadening the scope of the repository to begin making it a larger collection of information on hazard events such as earthquakes, hurricanes, tornadoes, windstorms, community-scale fires in the wildland urban interface, storm surges and human-made disasters (accidental, criminal or terrorist).As detailed in an accompanying guide, NIST Disaster and Failure Studies Data Repository: The Chile Earthquake Database--Ground Motion and Building Performance Data from the 2010 Chile Earthquake--User Manual (NIST GCR 15-1008), the new collection contains tabular data on ground motion, damage and structural properties, as well as nearly 25,000 photographs and drawings, for 273 buildings and structures impacted by the 2010 Maule, Chile, quake, and for comparison, their response to the 1985 quake centered offshore of Valparaíso, Chile, 370 kilometers (230 miles) to the north."Users can search the database by building names, design features, construction types, and uses and occupancies," says Long Phan, acting director of the NIST Disaster and Failure Studies Program.Next to be added to the repository will be data from the NIST investigation of the impacts of the May 22, 2011, tornado that struck Joplin, Missouri, and the NIST report that documents impacts of the May 20, 2013, tornado in the Newcastle-Moore area of Oklahoma.By making the data available online, NIST hopes to support the development of standards, codes, practices and new technologies that improve community resilience against the threat of disasters. As the repository grows, it will include data on significant hazard events; how buildings and other structures performed during those events; associated emergency response and evacuation procedures; and the technical, social and economic factors that affect pre-disaster mitigation activities and post-disaster response efforts. | Earthquakes | 2,016 |
April 25, 2016 | https://www.sciencedaily.com/releases/2016/04/160425113109.htm | Landslide risk remains high a year after magnitude-7.8 Nepal earthquake | With the monsoon fast approaching, the landslide risk in Nepal remains high a year after a magnitude-7.8 earthquake that killed more than 8,000 people, according to a University of Michigan-led research team. | The April 25, 2015, earthquake struck central Nepal and was followed two weeks later by a magnitude-7.2 aftershock. Both events produced strong ground shaking in the steep terrain of the Himalaya Mountains, causing widespread landsliding.In the past year, the U-M-led team has mapped 22,000 landslides caused by the Nepal earthquakes. The maps will be used to identify areas of continued high landslide risk, said Marin Clark, a U-M geomorphologist and geophysicist who studies tectonic movements in the Himalayas and who is an expert on landslides triggered by earthquakes.Hillsides stripped of vegetation by earthquake-generated landslides become hotspots for further landsliding during summer monsoon rainstorms, said Clark, an associate professor in the U-M Department of Earth and Environmental Sciences."While last year's monsoon was relatively mild, concern is high over what to expect this summer, if we were to have a normal or stronger-than-typical monsoon," Clark said. "We're releasing this new landslide inventory in time for the upcoming monsoon season so that government officials and aid organizations can use it to help a country that's still recovering from last year's disaster."With funding from the National Science Foundation, Clark and her colleagues have been studying the effects of last year's Nepal earthquakes on the landscape by analyzing where and why the landslides occurred. They used drones during the 2015 field season to help locate and map the landslides.Clark's collaborators on the study include Dimitrios Zekkos of the U-M College of Engineering and Joshua West of the University of Southern California. U-M graduate students Julie Bateman and Will Greenwood participated in the fall fieldwork, and undergraduate student Kevin Roback developed the digital landslide inventory.The highest density of Nepal landsliding, and therefore the location of highest ongoing risk, is concentrated in four large river valleys, one of which contains the main road from Nepal to China, Clark said.During the 2015 field season, the researchers also documented evidence of monsoon-related debris flows resulting from earthquake landslides. Debris flows are fast-moving mixtures of water, soil and rock. In Nepal following last year's earthquakes, debris flows impacted villages and temporarily blocked rivers, creating a flood risk.U-M graduate students will head back to Nepal next month to conduct additional fieldwork. Clark will return with a team of faculty researchers and students in the fall and is coordinating with groups from Switzerland and Germany. The landslide inventory and a related research article will be submitted for publication in a peer-reviewed journal. | Earthquakes | 2,016 |
April 21, 2016 | https://www.sciencedaily.com/releases/2016/04/160421112812.htm | Preparations for a US west coast tsunami look to the past and future | After the 2011 Tohoku earthquake and devastating tsunami in Japan, states such as California, Oregon, Washington and Alaska are looking to both the past and the future to prepare for a tsunami on the U.S. Pacific coastline. | Plans for managing tsunami risk on the West Coast are evolving, said scientists speaking at the Seismological Society of America's (SSA) 2016 Annual Meeting, held April 20-22 in Reno, Nevada. These plans include everything from tsunami hazard maps that guide the development of personal and community evacuation routes to detailed "playbooks" that help harbor and port officials recommend specific action plans based on tsunami forecast data.At the same time, geologists are searching for evidence of past tsunamis in the region to help them refine their estimates of tsunami risk. A SSA presentation by Robert Witter of the U.S. Geological Survey's Alaska Science Center, for instance, will discuss the evidence for frequent and large earthquakes and tsunamis occurring within the past 2000 years in parts of the Eastern Aleutian Islands. There are signs that these earthquakes have spanned the boundary between the locked and creeping portions of the region's megathrust fault. Earthquakes in the area could cause significant tsunami effects across the Pacific, especially in Hawaii and California."Despite the fact that we have learned a significant amount about the earthquake sources for tsunamis, there are gaps in our understanding of past tsunamis, especially prehistoric tsunamis," says Rick Wilson, a senior engineering geologist with the California Geological Survey. "If we can demonstrate when and where tsunamis occurred in the past, that information will give us a better understanding of the return periods in these areas, and that can go into the probabilistic analyses that help us understand our hazard and risk better."Wilson, who also serves as the science coordinator for the State of California Tsunami Preparedness and Hazard Mitigation Program, noted that more than 440,000 people have died worldwide since 1850 as a result of tsunamis. The deadly tsunamis caused by the 2004 Sumatran earthquake and the 2011 Tohoku earthquake brought increased public attention to tsunami science, warning and preparation.At the SSA meeting, Wilson will discuss how California officials used state tsunami response playbooks to respond to a tsunami advisory issued after the September 2015 magnitude 8.3 Illapel earthquake in Chile. The playbooks were created after the 2011 Tohoku earthquake, "when there was very little consistency between communities [in California] in what they did," Wilson says. "Some evacuated their entire zone, some just evacuated their beaches." The new playbooks offer a variety of action plans depending on the size of the tsunami from a distant source, Wilson says, "which gives officials more tools at the local level so that they can make these decisions, so that it's not an all or nothing approach."The impact of the 2011 Tohoku tsunami lingers in other ways in California. In her SSA presentation, geophysicist Lori Dengler of Humboldt State University will discuss how "Kamome," a Japanese boat caught in the 2011 tsunami that traveled across the ocean and beached near Crescent City, California in 2013, has become a powerful teaching tool in discussing earthquake and tsunami preparedness.The future of tsunami response and preparedness might come from new technologies such as camera-bearing drones that send video messages of incoming waves to convince coastal dwellers to evacuate, says Masa Hayashi, a retired IBM engineer presenting at the SSA meeting.And there's also the remote possibility that the trigger for a tsunami might not come from an earthquake, but from an asteroid strike on the Earth. In an SSA talk, Lawrence Livermore National Laboratory researcher Souheil Ezzedine will share data from a study that models the effects of an asteroid-generated tsunami (including the potential wave heights), on several coastline cities in the U.S., depending on the asteroid's impact off the U.S. East Coast, the Gulf of Mexico, and into the Pacific Ocean near San Francisco. | Earthquakes | 2,016 |
April 20, 2016 | https://www.sciencedaily.com/releases/2016/04/160420120317.htm | Induced earthquakes come under closer scrutiny | On March 28, the U.S. Geological Survey issued a one-year seismic forecast for the United States that for the first time includes ground-shaking hazards from both natural and human-induced earthquakes. In the wake of the forecast's release, researchers are gathering at the Seismological Society of America's (SSA) 2016 Annual Meeting April 20-22 in Reno, Nevada, to discuss some of the science behind the report. | Presenters at the meeting will speak about factors that may influence the location and strength of induced earthquakes in the central United States and western Canada and what can be done to minimize the occurrence and impacts of this seismic activity.The USGS report estimates that about 7 million people in the central and eastern United States now live in areas affected by induced earthquakes. In central Oklahoma and southern Kansas, there is a 5 to 12% chance of a damaging (magnitude 4.5 or larger) earthquake occurring within the next year. Other areas at risk for induced earthquake hazards include parts of Texas, Arkansas, Colorado, New Mexico, Ohio and Alabama. At the SSA meeting, Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project, will discuss the data that were used to build the new seismic forecast.The vast majority of induced seismicity in the United States is related to wastewater from enhanced oil recovery operations being injected back into the ground, says research geophysicist and deputy chief of the USGS Induced Seismicity Project Justin Rubinstein. At the SSA meeting, Rubinstein will discuss how places such as Harper and Sumner counties in southern Kansas have seen a surge in seismic activity since a 2012 increase in oil and gas operations in the area, including a magnitude 4.8 earthquake in 2014. When the Kansas Corporation Commission placed limits on the industry's wastewater disposal, Rubinstein reports, earthquake activity in the area under the limits decreased by 40 to 50% in the six months following the commission's order.A presentation by AECOM seismologist Ivan Wong will address one of the questions on the minds of infrastructure engineers and public policy planners after learning about the new USGS report: what is the potential for damage from these types of earthquakes? There is some disagreement among researchers, Wong notes, about whether the expected ground shaking in induced seismicity might be stronger or weaker in natural earthquakes. It may also be possible that even earthquakes of magnitude 5 or smaller could damage infrastructure in the central U.S. because buildings and roads in those regions have rarely been built with seismic hazards in mind.Several presentations in the induced seismicity session will examine whether there is a set of seismic features that can be used to distinguish natural from induced earthquakes. This remains a challenging problem, Rubinstein says, "since induced earthquakes involve the same sorts of slip processes as natural earthquakes." For the moment, induced earthquakes are identified by researchers looking at the full catalog of seismicity for a region, "and determining whether changes to industrial operations have coincided with changes in earthquake rates," he says.While the USGS report has raised new interest and concern about induced earthquakes in the central U.S., induced seismicity may have a relatively long history in the region, according to USGS seismologist Susan Hough, who will discuss 20thcentury oil and gas practices in Oklahoma in her SSA talk. She and her colleagues have turned up some interesting documents in the course of tracking down the roots of induced seismicity in the state, including a rare earthquake insurance policy taken out by an prominent Oklahoma City petroleum geologist in 1952, just a couple months before the magnitude 5.7 El Reno earthquake toppled buildings and chimneys and cracked the state capitol building in Oklahoma City. | Earthquakes | 2,016 |
April 18, 2016 | https://www.sciencedaily.com/releases/2016/04/160418092043.htm | Natural disasters since 1900: Over 8 million deaths, 7 trillion US dollars | More than seven trillion US dollars economic damage and eight million deaths via natural disasters since the start of the 20th century: These figures have been calculated and collected by the risk engineer Dr. James Daniell from Karlsruhe Institute of Technology (KIT). His database CATDAT looks at examining socioeconomic indicators as well as collecting and evaluating socioeconomic loss data through time, and has built a massive base for his post-disaster risk model which helps governments and aid organisations with catastrophe management and assessing rapidly the scale of a disaster. James will present his results at the 2016 European Geosciences Union General Assembly in Vienna. | As part of CATDAT, James Daniell has collected and evaluated over 35,000 natural disaster events since 1900 globally. Around a third of economic losses between 1900 and 2015 have been caused via floods. Earthquakes have caused around 26 percent of losses, Storms around 19 percent, Volcanic eruptions around 1 percent. "Over the last 100+ years the economic losses via natural disasters, in absolute terms, have increased," said Dr. Daniell, who conducts research at KIT as a John Monash Scholar is at the Geophysical Institute as well as the Center for Disaster Management and Risk Reduction Technology CEDIM. Over the whole time period, floods have caused the highest amount of economic losses, however, in recent times, since 1960, the highest percentage has switched to storm (and storm surge) with around 30% of losses.In relation to the current capital value of infrastructure and buildings in each country, the damage is reducing from natural catastrophes. "Less developed nations are often more vulnerable towards catastrophes -- that means relative to population and capital -- more deaths and higher economic losses are expected post-event," says the Civil/Structural engineer and Geophysicist. One common reason is the building quality itself in that building regulations and disaster codes even if present, are often not adhered to. In addition, the locations where people work (like in Bangladesh on the coasts), are economic centers and highly populated due to this, and the financial gains or livelihoods, often outweigh the potential disaster risks.For his analyses, he has created and collected many socioeconomic indices for the world, countries and often even provinces like human development, GDP, capital stock, exchange rates, price indices and data on security, building inventory and vulnerability in all countries exposed to disasters. In order to examine the trend of vulnerability over time, he normalised the losses to the year 2015 by examining the effect of historic events for today's conditions. "Here there is a clear trend, that many (but not all) countries are protecting themselves better against disasters by building better, and therefore and are reducing their risk of high losses," says Dr. Daniell. The improvements in flood protection are the most prominent when looking at the trends, as through the 1900-1960 time period, many huge events occurred, but from 1960 onwards, the normalised losses steadily reduce. The most visible reduction is seen in China and Japan.Depending on the metric used to convert event-year dollars to current 2015 dollars (i.e. consumer price index, building cost index or otherwise), the natural disaster damage bill is between 6.5 and 14 trillion USD. The 7 trillion USD bill from Dr. Daniell is based on a country-by-country GDP-deflator based price index, however the components of loss from natural disasters often differ significantly in addition to the loss estimate itself. "It is often impossible to get one exact value for a disaster event, as economic losses are often difficult to quantify, and death tolls are often overestimated (for example, the Haiti earthquake in 2010), or underestimated (like Uzbekistan in 1966)," he says, and therefore provides a lower and upper bound to his estimates of each past events from literature.Looking at the largest economic losses, the year 2011 with major earthquakes in Japan and New Zealand is the highest loss to date: "with around 335 billion USD direct damage, the Tohoku earthquake-tsunami-nuclear sequence on 11 March 2011 is the highest single-event natural catastrophe loss," says James Daniell. From the earthquake and following tsunami, around 18500 people died and around 450000 became homeless.Over 8 million deaths are shown in the CATDAT database since 1900 for earthquake, flood, storm, volcano and bushfires (withough counting deaths due to long term effects or drought/famine).The amount of deaths due to earthquake between 1900 and 2015 from the database at around 2.32 million (with a range of 2.18-2.63 million). Around 59 percent of them died as a result of the collapse of masonry buildings, and 28% of them due to secondary effects such as tsunami or landslides. Volcanic eruptions in the same time period have killed only 98,000 people (range: 83,000-107,000). However, volcanic eruptions before 1900, like the Tambora 1815 event, have the possibility to cause massive death tolls and also cause lower temperatures around the world leading to food security issues. "The absolute total of deaths through natural catastrophes has remained reasonably constant with a slight decrease. Around 50,000 people on average die each year. However, relative to population, death tolls have decreased significantly from 1900-2015," explains Dr. Daniell. "Over the entire time period, half of people died due to flood. However, with better planning, warnings and preventive measures, the death rate due to floods is signifcantly decreasing. Since 1960, earthquakes have caused the highest death percentage with around 40% of disaster deaths. Compared to the global death rate due to all causes, the rate of deaths due to natural disasters has remained quite constant.With each event over 100000 deaths, the 2004 Indian Ocean tsunami (around 230,000) and 2008 Cyclone Nargis (around 140000) in Myanmar are the largest disasters since 2000 in terms of deaths. The event with the highest death toll to date is the Great Floods of 1931 in China with a mean estimate around 2.5 million deaths.Since 2003, James Daniell has built the CATDAT Database from information out of Online Archives, books, reports from institutions, publications and other databases around the world, with original sources in over 90 languages. In his PhD dissertation, he developed a global rapid loss estimation model for earthquake, using empirical data from over 8000 earthquakes since 1900 and the associated socioeconomic climate over time. Using this basis, he has calculated a death toll estimate and economic loss estimate for each event since late 2009. At the start of 2016, Dr.-Ing. Daniell received one of three KIT Doctoral Awards from KIT awarded to dissertations finished in 2014. The model works very well for other disaster types, and he has continually updated his model with other natural catastrophes with over 35000 events collected since 1900, and many additional events pre-1900. | Earthquakes | 2,016 |
April 13, 2016 | https://www.sciencedaily.com/releases/2016/04/160413113416.htm | Earthquake may have been humanmade, but more data needed to assess hazards in Texas | The most comprehensive analysis to date of a series of earthquakes that included a 4.8 magnitude event in East Texas in 2012 has found it plausible that the earthquakes were caused by wastewater injection. The findings also underscore the difficulty of conclusively tying specific earthquakes to human activity using currently available subsurface data. | The study, conducted by researchers at The University of Texas at Austin Bureau of Economic Geology, was published April 13 in the To determine whether the earthquakes could have been caused by the injection of fluid into the underground geological formation, researchers built the first computer model for this site that simulates the effects of fluid injection on the stability of the fault that potentially generated the earthquakes. In their simulations, researchers used a range of likely values for input parameters. Those parameters included physical properties of the reservoir and the orientation of the fault. Earthquakes were generated using a certain range of input parameters, but no earthquakes were generated in simulations using a wider set of equally probable parameters.The 4.8 magnitude earthquake researchers looked at in this study occurred on May 17, 2012. It was the largest ever recorded in the area and followed a series of smaller earthquakes that started in April 2008, some 17 months after two wastewater injections wells began operating nearby. The wells are used to dispose of saline water that is produced with oil and gas from deep hydrocarbon reservoirs.The researchers tested a number of likely scenarios to assess if the volume and rate of fluid injected into the disposal wells were high enough to cause nearby faults to slip. Earthquakes occur when faults slip, a process that is aided by the high pressure generated in the porous rock formation during wastewater injection, but also occurs by natural tectonic processes.Previous studies relied on the timing and proximity of wastewater injection to earthquakes to decide if earthquakes were induced by human activity. This was the first to simulate the mechanics of an earthquake generated by water injection for this site."It is part of a continuing research effort by The University of Texas at Austin," said Peter Eichhubl, a senior research scientist at the Bureau of Economic Geology, which is the State Geological Survey of Texas and a research unit in The University of Texas Jackson School of Geosciences. "We used a more rigorous approach than previous studies, but our analyses are limited by the availability of robust, high-quality data sets that describe the conditions at depth at which water is injected and earthquakes occur. This study demonstrates the need for more and higher quality subsurface data to properly evaluate the hazards associated with wastewater injection in Texas."The relationship between seismic events, or earthquakes, and human activity has become more of a concern in recent years. While Oklahoma and Kansas are ranked highest in earthquake activity associated with oil and gas operations, Texas has experienced several earthquakes that have been linked to wastewater injection. The University of Texas at Austin is taking a leading role in the ongoing research. By the end of the year, the bureau will be operating a statewide network of seismographs called TexNet that will monitor, locate and catalog seismic activity with magnitude of 2 and greater.TexNet, which was authorized and funded by the Texas Legislature and Gov. Greg Abbott last year, will improve the state's ability to more rapidly and more accurately investigate earthquakes. Eichhubl said the data collected will help understand baseline seismicity and in so doing assist future studies that try to determine possible links between human activity and seismic events. | Earthquakes | 2,016 |
April 11, 2016 | https://www.sciencedaily.com/releases/2016/04/160411101119.htm | Hi-tech opens up Earth's secrets | JCU's Dr Rob Holm applied modern technology to existing geological data. He said the results open up completely new and original interpretations of geological processes. | "This research shows the value of applying new techniques to the extensive database of already existing scientific literature," he said."It can track the motion of tectonic plates to explain the formation of oceans and mountain ranges as these plates break apart and crash into one another, and even holds far-reaching implications for the distribution of animal species and Earth's climate though time."The animation shows the recent (from less than 8 million years ago) geological history of Papua New Guinea and the Solomon Islands. "Geologists can now see the different processes that are active in tectonic plates and mountain building in almost real time," said Dr Holm.He said it had revealed different geological relationships for the region, which had not been previously considered."This work highlights how the motion of tectonic plates and their related landmasses are intricately linked to the motion of other plates and plate boundaries surrounding them, and those further afield," he said.Dr Holm, a lecturer in petrology and mineralogy, said the work had more than theoretical applications. "We can now see the geological settings during the formation of mineral deposits rather than simply at the present day. As a result we gain a better understanding of the geological settings for deposit formation and can better predict worthwhile locations to explore."He said the work could also help with understanding and predicting earthquakes or volcanic eruptions. "It allows us to reconstruct and track the boundaries between tectonic plates. A better appreciation of this will give us a greater ability to predict where and when these hazards can occur."Dr Holm said the research illustrated the highly dynamic setting of the PNG and Solomon Islands region."Over a short geological time the Bismarck Sea has been created where no ocean previously existed, and the Solomon Sea has been reduced to a few 100 km across from what was once a vast ocean basin in excess of 1000 km wide, " he said.Dr Holm said the research will be expanded throughout the region to understand the evolution of the southwest Pacific, and also to investigate the long-term geological development of the region. | Earthquakes | 2,016 |
April 5, 2016 | https://www.sciencedaily.com/releases/2016/04/160405114218.htm | Slow fault movements may indicate impending earthquakes | Scientists from Nanyang Technological University (NTU Singapore) at its Earth Observatory of Singapore (EOS) have discovered a way to forecast earthquakes based on slow fault movements caused by moving sub layers of Earth. | So far, scientists believe that larger earthquakes are unlikely to occur following tremors or earthquakes below a Richter scale of 2 that are caused by small vibrations or slow fault movements such as those observed in the area of Parkfield along the San Andreas Fault in California, USA.However, the NTU team found that not only do these vibrations potentially point to an impending earthquake, they also discovered a discernible pattern to them."This discovery defied our understanding of how faults accumulate and release stress over time. These vibration patterns are caused by alternating slow and fast ruptures occurring on the same patch of a fault," said Asst Prof Sylvain Barbot, from NTU's Asian School of the Environment and an earth scientist at EOS."If only slow movements are detected, it does not mean that a large earthquake cannot happen there. On the contrary, the same area of the fault can rupture in a catastrophic earthquake," he warned.The study, which has major significance on the prediction of earthquakes, was led by Asst Prof Barbot's PhD student, Miss Deepa Mele Veedu. It was published in Seismic hazards in the Southeast Asia region will probably come from an impending large earthquake in the Mentawai seismic gap in Sumatra, Indonesia -- a current area of active monitoring and investigation.EOS scientists have earlier pointed out a large earthquake may occur any time in this area southwest of Padang -- the only place along a large fault where a big earthquake has not occurred in the past two centuries. The team's latest findings could potentially be applied in the seismic monitoring of the area to help better forecast large earthquakes in the region.EOS conducts fundamental research on earthquakes, volcanic eruptions, tsunamis and climate change in and around Southeast Asia, towards safer and more sustainable societies. | Earthquakes | 2,016 |
March 31, 2016 | https://www.sciencedaily.com/releases/2016/03/160331082518.htm | Researchers reproduce mechanism of slow earthquakes | Up until now catching lightning in a bottle has been easier than reproducing a range of earthquakes in the laboratory, according to a team of seismologists who can now duplicate the range of fault slip modes found during earthquakes, quiet periods and slow earthquakes. | "We were never able to make slow stick slip happen in the laboratory," said Christopher Marone, professor of geosciences, Penn State. "Our ability to systematically control stick velocity starts with this paper."The research, led by John Leeman, Ph.D. candidate in geoscience and including Marone, Demian Saffer, professor of geosciences at Penn State and Marco Scuderi, a former Ph.D. student in geosciences now at Sapienza Università di Roma, Italy, recreated the forces and motion required to generate slow earthquakes in the laboratory using ground quartz and a machine that can apply pressure on the materials altering stresses and other parameters to understand frictional processes."While regular earthquakes are catastrophic events with rupture velocities governed by elastic wave speed, the processes that underlie slow fault slip phenomena, including recent discoveries of tremor, slow-slip and low-frequency earthquakes, are less understood," the researchers report in Catastrophic earthquakes, the kind that destroy buildings and send people scurrying for doorways and safe locations, are caused when two tectonic plates that are sliding in opposite directions stick and then slip suddenly, releasing a large amount of energy, creating tremors and sometimes causing destruction. Along regions of faults that do not produce earthquakes, the two sides of the fault slowly slip past each other in a stable fashion. Slow earthquakes occur somewhere between the stable regime and fast stick slip.Regular earthquakes take place rapidly, while slow earthquakes occur on time scales that may range up to months. They can be as large as magnitude 7 or more and may be precursors to regular earthquakes. However, slow earthquakes propagate slowly and do not produce high-frequency seismic energy. They exist in the regime between stable slipping and regular earthquakes.The researchers applied stress perpendicular to the direction of shear and then applied forces to shear the ground quartz. By altering the amount of stress placed in the perpendicular direction, they could achieve the audible crack of a regular earthquake, stable slippage and a wide range of slip-stick behaviors including slow earthquake."What's really cool about this is that nobody has been able to systematically produce a slow earthquake, stable sticking, the whole range between a slow and fast earthquake," said Marone. | Earthquakes | 2,016 |
March 29, 2016 | https://www.sciencedaily.com/releases/2016/03/160329132238.htm | Fracking -- not wastewater disposal -- linked to most induced earthquakes in Western Canada | A survey of a major oil and natural gas-producing region in Western Canada suggests a link between hydraulic fracturing or "fracking" and induced earthquakes in the region, according to a new report published online in the journal | The study's findings differ from those reported from oil and gas fields in the central United States, where fracking is not considered to be the main cause of a sharp rise in induced seismicity in the region. Instead, the proliferation of hundreds of small earthquakes in that part of the U.S. is thought to be caused primarily by massive amounts of wastewater injected back into the ground after oil and gas recovery.The SRL study does not examine why induced seismicity would be linked to different processes in the central U.S. and western Canada. However, some oil and gas fields in the U.S., especially Oklahoma, use "very large amounts of water" in their operations, leading to much more wastewater disposal than in Canadian operations, said Gail M. Atkinson of Western University.It is possible that massive wastewater disposal in the U.S. is "masking another signal" of induced seismicity caused by fracking, Atkinson said. "So we're not entirely sure that there isn't more seismicity in the central U.S. from hydraulic fracturing than is widely recognized."The fracking process uses high-pressure injections of fluid to break apart rock and release trapped oil and natural gas. Both fracking and wastewater injections can increase the fluid pressure in the natural pores and fractures in rock, or change the state of stress on existing faults, to produce earthquakes.The Western Canada Sedimentary Basin (WCSB) contains one of the world's largest oil and gas reserves, and is dotted with thousands of fracking wells drilled in multi-stage horizontal operations. Atkinson and her colleagues compared the relationship of 12,289 fracking wells and 1236 wastewater disposal wells to magnitude 3 or larger earthquakes in an area of 454,000 square kilometers near the border between Alberta and British Columbia, between 1985 and 2015.The researchers performed statistical analyses to determine which earthquakes were most likely to be related to hydraulic fracturing, given their location and timing. The analyses identified earthquakes as being related to fracking if they took place close to a well and within a time window spanning the start of fracking to three months after its completion, and if other causes, such as wastewater disposal, were not involved.Atkinson and colleagues found 39 hydraulic fracturing wells (0.3% of the total of fracking wells studied), and 17 wastewater disposal wells (1% of the disposal wells studied) that could be linked to earthquakes of magnitude 3 or larger.While these percentages sound small, Atkinson pointed out that thousands of hydraulic fracturing wells are being drilled every year in the WCSB, increasing the likelihood of earthquake activity. "We haven't had a large earthquake near vulnerable infrastructure yet," she said, "but I think it's really just a matter of time before we start seeing damage coming out of this."The study also confirmed that in the last few years nearly all the region's overall seismicity of magnitude 3 or larger has been induced by human activity. More than 60% of these quakes are linked to hydraulic fracture, about 30-35% come from disposal wells, and only 5 to 10% of the earthquakes have a natural tectonic origin, Atkinson said.Atkinson said the new numbers could be used to recalculate the seismic hazard for the region, which could impact everything from building codes to safety assessments of critical infrastructure such as dams and bridges. "Everything has been designed and assessed in terms of earthquake hazard in the past, considering the natural hazard," she said. "And now we've fundamentally changed that, and so our seismic hazard picture has changed."The researchers were also surprised to find that their data showed no relationship between the volume of fluid injected at a hydraulic fracturing well site and the maximum magnitude of its induced earthquake."It had previously been believed that hydraulic fracturing couldn't trigger larger earthquakes because the fluid volumes were so small compared to that of a disposal well," Atkinson explained. "But if there isn't any relationship between the maximum magnitude and the fluid disposal, then potentially one could trigger larger events if the fluid pressures find their way to a suitably stressed fault."Atkinson and her colleagues hope to refine their analyses to include other variables, such as information about extraction processes and the geology at individual well sites, "to help us understand why some areas seem much more prone to induced seismicity than others."The scientists say the seismic risks associated with hydraulic fracturing could increase as oil and gas companies expand fracking's use in developing countries, which often contain dense populations and earthquake-vulnerable infrastructure. | Earthquakes | 2,016 |
March 14, 2016 | https://www.sciencedaily.com/releases/2016/03/160314140731.htm | Gravity glasses offer a view of the Earth's interior | How does the ice on the polar caps change? And which are the geological characteristics of the Earth's crust beneath? What is the structure of the boundary between the Earth's crust and mantle? Geophysicists will be able to answer these questions in the future using gravity field measurements from ESA's GOCE gravity satellite. Geodesists from the Technical University of Munich (TUM) have prepared the measurement data mathematically in such a way that they can be used to resolve structures deep below the surface. | If an astronaut could see gravity fields, then he would not perceive the Earth as round; instead, it would appear dented like a potato. The reason: the masses in oceans, continents and deep in the Earth's interior are not distributed equally. The gravitational force therefore differs from location to location. These variations, which are invisible to the human eye, have been measured by highly sensitive acceleration sensors on board the Gravity Field and Steady-State Ocean Circulation Explorer -- GOCE for short.The satellite transmitted several hundred million data records to ground control between 2009 and 2013. Groups of the TUM are significantly involved in the development of the mission and the analysis and application of the measurements. "This data has helped us to map the Earth's gravity field with great precision. And now -- by putting on the gravity glasses -- we can use the measurement values to see deep beneath the surface of our planet," explains Dr. Johannes Bouman from the German Geodetic Research Institute at TUM.On the gravity field maps that the team has now published in the online magazine Together with his team Bouman worked on preparing the GOCE data for two years. This data proved difficult to interpret because the satellite's height and orientation fluctuated as it orbited the Earth. "The location of the satellite could be pinpointed at any time using GPS, but you had to correlate each measurement with the coordinates saved when evaluating the data," recalls the TUM researcher. Using the algorithms that he developed with his team, he was able to transform the data in such a way as to enable geophysicists to use it without additional adjustments going forward.The trick: the measurement values were not correlated with the actual trajectory of the satellite; instead, they were converted into two reference ellipsoids. These ellipsoids, which surround the Earth at heights of 225 and 255 kilometers, have a fixed height and their geographical orientation is defined, too. Each ellipsoid consists of 1.6 million grid points that can be combined. "In this way -- as with stereoscopic vision with two eyes -- you can make the third dimension visible. If you then combine this information with a geophysical model, you get a three-dimensional image of the Earth," explains Bouman."This method is very interesting for geophysicists," emphasizes Prof. Jörg Ebbing, Head of the Work Group for Geophysics and Geoinformation at the University of Kiel and also author of the paper. "Previously, the models were predominantly based on seismic measurements -- from the course that seismic waves travel, you can deduce, for example, boundaries between the Earth's crust and mantle. This new data allows us to check and improve our ideas and perceptions."Analyzing the Earth's crust in the North Atlantic is only the beginning. "Using the geodetic data from the GOCE mission, we will be able to examine the structure of the entire crust in more detail in the future," adds Prof. Florian Seitz, Director of the German Geodetic Research Institute at TUM. "And we will even be able to make dynamic movements visible, such as the melting of the polar ice sheets, which seismology could not see." | Earthquakes | 2,016 |
March 10, 2016 | https://www.sciencedaily.com/releases/2016/03/160310080824.htm | Continuous leaking of radioactive strontium, cesium from Fukushima to the ocean | Scientists from the Universitat Autònoma de Barcelona (UAB) investigated the levels of radioactive strontium and cesium in the coast off Japan in September 2013. Radioactive levels in seawater were 10 to 100 times higher than before the nuclear accident, particularly near the facility, suggesting that water containing strontium and cesium isotopes was still leaking into the Pacific Ocean. | March 11 will be the 5th anniversary since the nuclear accident in Fukushima, Japan. The Tohoku earthquake and the series of tsunamis damaged the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) causing a massive release of radioactivity into the atmosphere and the Pacific Ocean. Since then, the Tokyo Electric Power Company (TEPCO) and the Japanese authorities have focused on controlling the water flowing in and out of the FDNPP and on decontaminating the highly radioactive water used as coolant for the damaged reactors (about 300 m3 a day, cubic meter = 1000 L). This cooling water is then stored in tanks and, to some extent, being decontaminated.A new study recently published in Environmental Science and Technology, uses data on the concentrations of 90Sr and 134,137Cs in the coast off Japan from the moment of the accident until September 2013, and puts it into a longer-time perspective including published data and TEPCO's monitoring data available until June 2015. This study continues the work initiated after the accident in 2011 by some of the authors. These and other partners from Belgium and Japan are currently involved in the European FRAME project lead by Dr. Pere Masqué that aims at studying the impact of recent releases from the Fukushima nuclear accident on the marine environment. FRAME is encompassed within the European COMET project (Seawater collected from the sea surface down to 500 m between 1 and 110 km off the FDNPP showed concentrations up to 9, 124 and 54 Bq·m−3 for 90Sr, 137Cs and 134Cs, respectively. The highest concentrations, found within 6 km off the FDNPP, were approximately 9, 100 and 50 times higher, respectively, than pre-Fukushima levels. Before the accident, the main source of these radionuclides was atmospheric deposition due to nuclear bomb testing performed in the 1950s and 1960s. The presence of 134Cs (undetectable before the accident) and the distinct relationship between 90Sr and 137Cs in the samples suggested that FDNPP was leaking 90Sr at a rate of 2,3 -- 8,5 GBq d-1 (giga-Becquerel per day) into the Pacific Ocean in September 2013. Such a leak would be 100-1000 times larger than the amount of 90Sr transported by rivers from land to ocean. Additional risk is related to the large amounts of water stored in tanks that have frequently leaked in the past. These results are in agreement with TEPCO's monitoring data which show levels of 90Sr and 137Cs up to 10 and 1000 times higher than pre-Fukushima near the discharge channels of the FDNPP until June 2015 (most recent data included in the study). The presence of 90Sr and 134,137Cs in significant amounts until 2015 suggests the need of a continuous monitoring of artificial radionuclides in the Pacific Ocean. | Earthquakes | 2,016 |
March 7, 2016 | https://www.sciencedaily.com/releases/2016/03/160307113303.htm | Faults control the amount of water flowing into the Earth during continental breakup | New light has been shed on the processes by which ocean water enters the solid Earth during continental breakup. | Research led by geoscientists at the University of Southampton, and published in When water and carbon is transferred from the ocean to the mantle it reacts with a dry rock called peridotite, which makes up most of the mantle beneath the crust, to form serpentinite.Dr Gaye Bayrakci, Research Fellow in Geophysics, and Professor Tim Minshull, from Ocean and Earth Science, with colleagues at the University of Southampton and six other institutions, measured the amount of water that had entered the Earth by using sound waves to map the distribution of serpentinite.The sound waves travel through the crust and mantle and can be detected by sensitive instruments placed on the ocean floor. The time taken for the signals to travel from an acoustic seismic source to the seafloor instruments reveals how fast sound travels in the rocks, and the amount of serpentinite present can be determined from this speed.The four-month experiment, which involved two research ships (the R/V Marcus Langseth and the F/S Poseidon), mapped an 80 by 20 km area of seafloor west of Spain called the Deep Galicia Margin where the fault structures were formed when North America broke away from Europe about 120 million years ago.The results showed that the amount of serpentinite formed at the bottom of each fault was directly proportional to the displacement on that fault, which in turn is closely related to the duration of fault activity.Dr Bayracki said: "One of the aims of our survey was to explore the relationship between the faults, which we knew already were there, and the presence of serpentinite, which we also knew was there but knew little about its distribution. The link between fault activity and formation of serpentinite was something we might have hoped for but did not really expect to see so clearly."This implies that seawater reaches the mantle only when the faults are active and that brittle processes in the crust may ultimately control the global amount of seawater entering the solid Earth."In other tectonic settings where serpentinite is present such as mid ocean ridges and subduction zones, the focused flow of seawater along faults provides a setting for diverse hydrothermal ecosystems where life-forms live off the chemicals stripped out of the rocks by the water as it flows into and then out of the Earth's mantle.The researchers were able to estimate the average rate at which seawater entered the mantle through the faults at the Deep Galicia Margin and discovered that rate was comparable to those estimated for water circulation in hot rock at mid-ocean ridges, where such life-forms are more common. These results suggest that in continental rifting environment there may have been hydrothermal systems, which are known to support diverse ecosystems.Co-Author and Professor of Geology at the University of Birmingham Tim Reston commented: "Understanding the transport of water during deformation has broad implications, ranging from hydrothermal systems to earthquake mechanics. The new results suggest a more direct link between faulting and water movements than we previously suspected." | Earthquakes | 2,016 |
March 2, 2016 | https://www.sciencedaily.com/releases/2016/03/160302135618.htm | Invigorating Japanese energy and environmental policy five years after Fukushima | Japanese researchers call for increased interdisciplinarity and internationalization in Japanese energy and environment research to provide effective scientific advice and invigorate Japanese energy and environmental policy five years after Fukushima. | In less than two weeks, it will be five years since the Great East Japan Earthquake and tsunami killed over 15,000 people and crippled the Fukushima Daiichi nuclear power plant. While Japan has implemented new energy and environment polices after the March 11 disaster, many issues remain unsettled surrounding nuclear safety, renewable energy policy, and reactor decommissioning.In a forthcoming comment in "There is a tendency or custom for Japanese researchers working on policy-relevant research to publish only in Japanese," says Sugiyama. "This is natural. Japanese is the native language of the Japanese policymakers their research targets. However, unlike traditional disciplines where Japan boasts Nobel laureates, there is a limited pool of researchers in Japan who can scrutinize and critique this interdisciplinary research. Internationalizing Japanese research will expand the pool of researchers who can contribute to this process."Sugiyama and his colleagues also decry the lack of interdisciplinarity in Japanese research, citing probabilistic risk assessment (PRA) research as an example. PRA is a tool used to evaluate accident risk employed in Japanese nuclear power plants, but prior to the earthquake, PRA research focused on mechanical failures and human error from an engineering perspective and did not incorporate perspectives from seismology, geology, atmospheric science and ecological modeling. This is in contrast to PRA research in other nuclear-reliant countries such as the United States, United Kingdom, and France."Hearing the difficulty of interdisciplinary research, people often imagine the gap between the natural and social sciences. This is indeed a challenge. But in Japan, even efforts to connect the natural sciences and engineering disciplines have not been successful," says co-author Professor Hideaki Shiroyama of the Graduate Schools for Law and Politics.The authors suggest that Japanese publishers and major Japanese granting programs such as KAKENHI should include non-Japanese researchers in their review process, Japanese funding agencies should require scientists working on policy-oriented research to publish part of their results in international journals and that strategic, policy-oriented research programs should be designed so that projects can benefit from international experience and experience can be shared globally."The worldwide impact of March 11 is just one example," says PARI's Professor Taketoshi Taniguchi, another co-author. "I hope the research community will take the lead in globalizing research, which can then provide a stepping-stone to globalizing policy discourse." | Earthquakes | 2,016 |
March 2, 2016 | https://www.sciencedaily.com/releases/2016/03/160302135559.htm | New study pinpoints stress factor of mega-earthquake off Japan | Scripps Institution of Oceanography, UC San Diego researchers published new findings on the role geological rock formations offshore of Japan played in producing the massive 2011 Tohoku-oki earthquake, one of only two magnitude 9 mega-earthquakes to occur in the last 50 years. | The study, published in the journal The magnitude 9 quake, which triggered a major tsunami that caused widespread destruction along the coastline of Japan, including the Fukushima nuclear plant disaster, was atypical in that it created an unusually large seismic movement, or slip, of 50 meters (164 feet) within a relatively small rupture area along the earthquake fault.To better understand what may have caused this large movement, Scripps researchers used gravity and topography data to produce a detailed map of the geological architecture of the seafloor offshore of Japan. The map showed that the median tectonic line, which separates two distinct rock formations, volcanic rocks on one side and metamorphic rocks on the other, extends along the seafloor offshore.The region over the earthquake-generating portion of the plate boundary off Japan is characterized by variations in water depth and steep topographic gradients of about six kilometers (3.7 miles). These gradients, according to the researchers, can hide smaller variations in the topography and gravity fields that may be associated with geological structure changes of the overriding Japan and subducting Pacific plates."The new method we developed has enabled us to consider how changes in the composition of Japan's seafloor crust along the plate-boundary influences the earthquake cycle," said Dan Bassett, a postdoctoral researcher at Scripps and lead author of the study.The researchers suggest that a large amount of stress built up along the north, volcanic rock side of the median tectonic line resulting in the earthquake's large movement. The plates on the south side of the line do not build up as much stress, and large earthquakes have not occurred there."There's a dramatic change in the geology that parallels the earthquake cycle," said Scripps geophysicist David Sandwell, a co-author of the study. "By looking at the structures of overriding plates, we can better understand how big the next one will be." | Earthquakes | 2,016 |
March 1, 2016 | https://www.sciencedaily.com/releases/2016/03/160301104200.htm | Earthquake research in New Zealand on damaged buildings | In 2010 and 2011, the Canterbury region of New Zealand experienced an extended sequence of earthquakes, with the two most prominent events occurring on September 4, 2010 (Darfield earthquake, MW 7.1) and February 22, 2011 (Christchurch earthquake, MW 6.2). The earthquakes caused significant ductility demands and corresponding damage in many multi-story commercial and residential buildings in Christchurch, the largest city in the region. | Assessment of the extent of earthquake damage and the residual capacity of buildings following the earthquakes proved to be a challenging task for building owners, insurers, and structural engineers throughout New Zealand. As a result of these decisions, a significant portion of modern reinforced concrete (RC) multi-story buildings were demolished. The demolition of these buildings provided a unique opportunity to extract and test components from such structures.The Clarendon Tower was a twenty-story office building located in the city center of Christchurch. The tower was designed in 1987 and was constructed primarily of RC, using both precast and cast-in-place elements as was common in New Zealand at the time of construction. The September 4, 2010 and February 22, 2011 earthquakes subjected the Clarendon Tower to approximate peak ground accelerations of 0.22g and 0.43g, respectively. Maximum displacement ductility demand near mid-height of the building was estimated to be as high as 4.0 during the February 22, 2011 earthquake.During the deconstruction of the Clarendon Tower, three precast RC moment-resisting frame components were extracted from the building for structural testing in order to assess the residual capacity and reparability of the frames. This research program, described in an upcoming article in the ACI Structural Journal, involved testing these full-scale components that are amongst the largest beam-column joint sub-assemblies that have been tested in New Zealand, and are thought to be amongst the largest components worldwide to be extracted and tested from an actual building and, in particular, from an earthquake-damaged building.The extracted RC frames were repaired using various techniques based on the extent of damage and then subjected to simulated seismic loading. Due to the size of the test components, a custom-designed steel reaction frame was utilized. The experimental testing involved collaboration between researchers at the University of Auckland and practicing engineers at Compusoft Engineering Ltd.The results of the experimental tests indicated that the frames could withstand significant inelastic deformations following repairs, consistent with the expected performance of comparable undamaged frames. Given the prototypical detailing of the some of the tested elements, the experimental tests also provided an opportunity to verify the expected seismic behavior of precast RC buildings constructed in New Zealand in the 1980s, as well as provide critical evidence to improve the assessment of post-earthquake residual capacity. The authors believe that these findings will help to reduce the uncertainty of post-earthquake assessments and lead to better informed decision-making following future earthquakes. The Clarendon Tower frame test program is one of a number of projects being conducted at the University of Auckland to understand and learn from buildings damaged during the Canterbury earthquake series in order to ultimately improve design standards for new buildings and assessment guidelines for existing buildings. | Earthquakes | 2,016 |
February 16, 2016 | https://www.sciencedaily.com/releases/2016/02/160216181702.htm | Breaking the strongest link triggered Big Baja Earthquake | A spate of major earthquakes on small faults could overturn traditional views about how earthquakes start, according to a study from researchers at the Centro de Investigación Científica y de Educación Superior in Ensenada, Mexico, and the University of California, Davis. | The study, published Feb. 15 in the journal In the past 25 years, many of California's biggest earthquakes struck on small faults, away from the San Andreas Fault plate boundary. These events include the Landers, Hector Mine and Napa earthquakes. Several of the quakes were unexpected, rattling areas thought seismically quiet.A closer look at one of the surprise events, the magnitude-7.2 El Mayor-Cucapah earthquake, showed that small faults may often link together along a "keystone" fault. A keystone is the central stone that holds a masonry structure together. During the El Mayor-Cucapah earthquake, the keystone fault broke first, unlocking seven smaller faults, the study found.However, the research team discovered that of all the faults unzipped during the El Mayor-Cucapah earthquake, the keystone fault was not the one closest to breaking."One of the important outcomes of this study is you can have a whole network of faults activated together by one underpinning fault, and that's an important concern," said study co-author Michael Oskin, a UC Davis professor of geology. "An earthquake involving a system of small faults can be more damaging than a single event because it increases the amount of seismic energy released."The April 4, 2010, El Mayor-Cucapah earthquake leapfrogged across seven faults and jumped a 5-mile wide gap. The researchers used a wealth of recorded seismic data and detailed mapping of surface changes to reconstruct the complex earthquake sequence.The study reveals the underlying reason for this unusual pattern: a hidden fault buried at a shallow angle to the surface. Each of the seven faults steeply dips toward this hidden fault, linking up deep underground.Lead author John Fletcher, a professor at CICESE, likened the system to a house of cards -- remove one key piece and the entire structure tumbles."The trick here is the cards can bend, but it isn't until one particular fault goes that the whole set ruptures," Fletcher said.The El Mayor-Cucapah earthquake occurred in a transition zone, between faults spreading open to form the Gulf of California and faults where the Pacific and North America tectonic plates slip sideways past one another. The earthquake was centered about 30 miles south-southeast of Mexicali in northern Baja California, Mexico.The results suggest similar processes are at work in other areas where the Earth's crust accommodates major changes in shape."This gives us insight into how those messy things between the main faults work," Oskin said. "This might be pretty common."In past events, the signal of a low-angle fault could have been masked because it activated a lot of high-angle faults in the same earthquake, the researchers said.The idea could also explain a longstanding mystery: why the central San Andreas fault is almost perpendicular to its stress field. Oskin said the central San Andreas fault may also behave like a keystone fault.The El Mayor-Cucapah earthquake caused extensive damage to the city of Mexicali, displacing more than 35,000 people and causing two deaths. The shaking demolished roads and irrigation channels in surrounding agricultural areas. Reports documented widespread liquefaction, road ruptures, cracked infrastructure, tilting power line towers and partial or total collapse of many buildings. Damage topped $440 million in the Mexicali Valley and $90 million in California's Imperial Valley.Orlando Teran, a recent Ph.D. graduate with CICESE also co-authored the report.The study was funded by the National Council of Science and Technology (CONACYT), National Science Foundation and the Southern California Earthquake Center. | Earthquakes | 2,016 |
February 12, 2016 | https://www.sciencedaily.com/releases/2016/02/160212163857.htm | New app turns smartphones into worldwide seismic network | University of California, Berkeley, scientists are releasing a free Android app that taps a smartphone's ability to record ground shaking from an earthquake, with the goal of creating a worldwide seismic detection network that could eventually warn users of impending jolts from nearby quakes. | The app, called MyShake, will be available to the public Friday, Feb. 12, from the Google Play Store and runs in the background with little power, so that a phone's onboard accelerometers can record local shaking any time of the day or night. For now, the app only collects information from the accelerometers, analyzes it and, if it fits the vibrational profile of a quake, relays it and the phone's GPS coordinates to the Berkeley Seismological Laboratory for analysis.Once enough people are using it and the bugs are worked out, however, UC Berkeley seismologists plan to use the data to warn people miles from ground zero that shaking is rumbling their way. An iPhone app is also planned."MyShake cannot replace traditional seismic networks like those run by the U.S. Geological Survey, UC Berkeley, the University of Washington and Caltech, but we think MyShake can make earthquake early warning faster and more accurate in areas that have a traditional seismic network, and can provide life-saving early warning in countries that have no seismic network," said Richard Allen, the leader of the app project, director of the Berkeley Seismological Laboratory and a professor and chair of the Department of Earth and Planetary Sciences. The lab operates a sensitive but widely spaced network of seismic sensors buried in vaults around Northern CaliforniaA crowdsourced seismic network may be the only option today for many earthquake-prone developing countries, such as Nepal or Peru, that have a sparse or no ground-based seismic network or early warning system, but do have millions of smartphone users."In my opinion, this is cutting-edge research that will transform seismology," said UC Berkeley graduate student Qingkai Kong, who developed the algorithm at the heart of the app. "The stations we have for traditional seismology are not that dense, especially in some regions around the world, but using smart phones with low-cost sensors will give us a really good, dense network in the future."Smartphones can easily measure movement caused by a quake because they have three built-in accelerometers designed to sense the orientation of the phone for display or gaming. While constantly improving in sensitivity for the benefit of gamers, however, smartphone accelerometers are far less sensitive than in-ground seismometers. But they are sensitive enough to record earthquakes above a magnitude 5 -- the ones that do damage -- within 10 kilometers. And what these accelerometers lack in sensitivity, they make up for in ubiquity. There are an estimated 16 million smartphones in California, and 1 billion smartphones worldwide."Currently, we have a network of 400 seismic stations in California, one of the densest in the world," Allen said. "Even if we get only a small fraction of the state's 16 million mobile phones participating in our program, that would be a many-orders-of-magnitude increase in the amount of data we can gather."In a paper to be published in the Feb. 12 issue of the journal Allen hopes that thousands of people will download and install the app so that he and his colleagues can give MyShake a good test. If successful, he anticipates an updated app that provides early warning within a year.He will discuss MyShake and other earthquake early warning systems during a scientific session on Friday, Feb. 12, 10-11:30 a.m. EST, during the annual meeting of the American Association for the Advancement of Science in Washington, D.C.A West Coast early warning system got a big boost in this year's federal budget when $8.2 million was appropriated to help the U.S.G.S. create such a system in conjunction with UC Berkeley, the universities of Washington and Oregon and Caltech. Allen and other seismologists gathered on Feb. 2 at the White House to discuss earthquake early warning plans and a new initiative to make all federal buildings earthquake-proof.An early warning system along America's earthquake-prone Pacific edge would be based on a prototype called ShakeAlert now undergoing testing in California, Oregon and Washington. In the San Francisco Bay Area, agencies such as the Bay Area Rapid Transit system already receive warnings from ShakeAlert, such as a 5-second alert after the 6.0 magnitude quake that struck nearby Napa in August 2014. At the White House meeting last week, the Gordon and Betty Moore Foundation committed $3 million to further develop ShakeAlert, and another $1 million for MyShake.In simulated tests based on real earthquakes, MyShake was able to provide timely early warning as well as or better than ShakeAlert.Researchers have made other attempts to harness the public's computers or mobile phones for earthquake detection, mostly using their power-hungry connection to the global GPS network, but it has been hard to keep users, especially when software updates interfere with ease of use."With an app, you have access to millions of phones and the Google Play Store and Apple iTunes make is easy to distribute," Allen said.Allen's long-term goal is to make earthquake detection so valuable that it becomes embedded in the mobile phone operating system, so that everyone becomes part of the network.The algorithm behind MyShake was turned into an app by programmers at the Silicon Valley Innovation Center in Mountain View, Calif., which is part of the Telekom Innovation Laboratories (T-Labs) operated by Deutsche Telekom, owner of T-Mobile. Over the past three years, as many as a eight people helped develop the computer code that ties the sensors to the analysis algorithm, and then uploads the data to servers at UC Berkeley."This is really novel and inventive science, so we spent a lot of time on analysis, making sure the basics of the app were fine," said Schreier, the vice president of the T-Labs innovation center. "We wanted an app that could collect the data needed, but wouldn't lock up the phone, or use up all the phone's memory, or burn out a battery, any of which would cause people not to use it."Kong then tested the algorithm, initially with 75 Android users from a class Allen taught, as well as friends and colleagues. T-Labs also provided phones that Kong tested on shake tables at UC Berkeley, which realistically simulate the vibrations from large quakes such as the 1989 Loma Prieta earthquake south of San Francisco.The app continually monitors the phone's accelerometers and tests every motion to see if it fits the profile of an earthquake. If the algorithm decides that the shaking it from a quake, it immediately sends basic information to UC Berkeley: the time and amplitude of the shaking, and the phone's position as measured by GPS. Cloud-based software constantly reviews all incoming data and, if at least four phones detect shaking and this represents more than 60 percent of all phones within a 10-kilometer radius of the epicenter, the program confirms an earthquake. The researchers cross-check this with the California Integrated Seismic Network, which monitors earth movement all over the state using underground seismometers."Now, ShakeAlert only issues alerts when four of our traditional seismic stations are triggered," Allen said. "But if we also have mobile phone data, maybe we would need only one station to trigger before issuing an alert."The app records accelerometer data continually, and after a confirmed earthquake will also send five minutes of data to the researchers, starting one minute before the quake and ending four minutes after. This happens only when the phone is plugged in and connected to a wifi network, however.Once the app has proven reliable, earthquake detection could trigger an alert to cellphone users outside ground zero, providing users with a countdown until shaking arrives."We need at least 300 smartphones within a 110-kilometer-by-110-kilometer area in order to have a reasonable estimate of the location, magnitude and origin time of an earthquake," Kong said. "The denser the network, the earlier you can detect the earthquake."With a dense enough network, detection, analysis and warning can take less than a second."We want to make this a killer app, where you put it on your phone and allow us use your accelerometer, and we will deliver earthquake early warning," Allen said.Young-Woo Kwon of Utah State University is also a co-author of the paper. | Earthquakes | 2,016 |
February 10, 2016 | https://www.sciencedaily.com/releases/2016/02/160210170137.htm | New cause of strong earthquakes found | A geologic event known as diking can cause strong earthquakes -- with a magnitude between 6 and 7, according to an international research team. | Diking can occur all over the world but most often occurs in areas where Earth's tectonic plates are moving apart, such as Iceland, Hawaii and parts of Africa in the East African Rift System. As plates spread apart, magma from beneath Earth's surface rises into the space, forming vertical magma intrusions, known as dikes. The dike pushes on the surrounding rocks, creating strain."Diking is a known phenomenon, but it has not been observed by geophysical techniques often," said Christelle Wauthier, assistant professor of geosciences, Penn State who led the study. "We know it's linked with rift opening and it has implications on plate tectonics. Here, we see that it also could pose hazards to nearby communities."The team investigated ties between two natural disasters from 2002 in the Democratic Republic of the Congo, East African Rift System. On Jan. 17, the Nyiragongo volcano erupted, killing more than 100 people and leaving more than 100,000 people homeless. Eight months later a magnitude 6.2 earthquake struck the town of Kalehe, which is 12 miles from the Nyiragongo volcano. Several people died during the Oct. 24 earthquake, and Kalehe was inundated with water from nearby Lake Kivu."The Kalehe earthquake was the largest recorded in the Lake Kivu area, and we wanted to find out whether it was coincidence that, eight months before the earthquake, Nyiragongo erupted," said Wauthier.The researchers used a remote sensing technique, Interferometric Synthetic Aperture Radar, to measure changes to Earth's surface before and after both natural disasters."This technique produces ground surface deformation maps. Then, you can invert those deformation maps to find a source that could explain the observed deformation. For the deformation observed in January 2002, we found that the most likely explanation, or best-fitting model, was a 12-mile diking intrusion in between Nyiragongo and Kalehe," said Wauthier.The researchers used the same technique for the October 2002 magnitude 6.2 earthquake, analyzing seismicity in addition to ground-deformation changes. They found that there was a fault on the border of the East African Rift System that slipped, triggering the earthquake."We were able to identify the type of fault that slipped, and we also had the best-fitting model for the dike intrusion," said Wauthier. "Knowing both of those, we performed a Coulomb stress-change analysis and found that the January 2002 dike could have induced the October 2002 earthquake."Coulomb stress-change analysis is a modeling technique that calculates the stress changes induced by a deformation source at potential receiver faults throughout a region. If the Coulomb stress changes are positive, it means that the source is bringing the receiver fault closer to failure -- closer to slipping and generating an earthquake. This type of analysis is regularly applied to assess whether an earthquake in one region could trigger a secondary earthquake nearby.The researchers hypothesized that the dike opening pushed outward against the adjacent rocks. These rocks became strained and passed stress to rocks adjacent to them, accumulating stress on rocks on a fault in the Kalehe area. The dike brought this fault closer to failure and, eight months later, a small stress perturbation could have triggered the start of the magnitude 6.2 earthquake."We've known that every time magma flows through Earth's crust, you create stress and generate seismicity," said Wauthier. "But these are normally very low magnitude earthquakes. This study suggests that a diking event has the potential to lead to a large earthquake," said Wauthier.The researchers report their findings in the current issue of | Earthquakes | 2,016 |
February 9, 2016 | https://www.sciencedaily.com/releases/2016/02/160209132043.htm | Protect your Chicago water heater against earthquakes? There's a better bet | Chicago homeowners, take note: you'll get a better return on your investment if you buy a lottery ticket when the jackpot is high, rather than pay to secure your water heater against earthquake damage. | That's the conclusion of a Northwestern University class of geosciences and civil engineering students who decided to estimate these costs and benefits after an Illinois Emergency Management Agency spokesperson urged Illinois residents to protect their water heaters against earthquakes.Led by Northwestern professor and seismologist Seth Stein, the class estimated that there would be a net benefit to strapping the water heater to wall studs if there was a high probability that the heater would suffer major damage due to an earthquake during its ten-year average lifespan. But this would require earthquake shaking strong enough to topple heavy furniture, which as far as anyone knows, has never happened in northern Illinois. Even in the southernmost part of the state, such strong shaking hasn't happened since the New Madrid earthquakes of 1811-1812.You'll get a better rate of return on your money, the class suggests, if you buy a ticket for a big-jackpot lottery like Powerball. When jackpots are high--over $288 million--there is a net benefit to buying a ticket, because the odds are such that you are likely to win at least some money with your ticket. And those big jackpots come around much more often than big Chicago earthquakes--about 5% of the biweekly Powerball drawings are for a jackpot of $288 million or more, including the recent $1.5 billion Powerball drawing on January 13.The water heater study was guided by Stein's textbook Playing against Nature: Integrating Science and Economics to Mitigate Natural Hazards in an Uncertain World, written with his father, the late Jerome Stein, a professor emeritus of economics at Brown University. The book demonstrates how combining science, economics and risk analysis can aid policymakers as they prepare for floods, earthquakes and droughts.This approach was just what Edward Brooks, a graduate student in seismology and lead author on the paper, was looking for after shifting his research interests from physics to geophysics in the wake of the devastation caused by the 2011 Tohoku earthquake in Japan. "This course perfectly captured what I personally think are the most interesting questions in earth science," he said. "How do we prepare for an uncertain future? What is the best way to invest our present resources? How can we improve our models and predictions in the future?"In the case of the water heaters, the students used Fermi estimation techniques, named after physicist and Nobel Prize winner Enrico Fermi. Fermi was famous for simple estimates of complex quantities, such as the problem that he posed to students: how many piano tuners are there in Chicago? His technique breaks down the problem into estimating simpler quantities--How many Chicago households have a piano? How many times a year are pianos tuned?--that can be combined to produce a good estimate for the original question."The idea of using the Fermi approach is that you know that you can't get these things exactly right, because you're dealing with unknowns in the future," Stein said. "But you can make reasonable estimates, and what's nice is that the answers are pretty robust; you can put different values in but general answer is about the same."The class divided the water heater question into smaller inquiries, including how much it would cost to secure a water heater, how often and in what ways might water heaters be damaged, whether insurance would cover these costs, and how often earthquake shaking of a specific level might occur in Chicago."Before this class I had not thought about how I would explain a scientific decision to a policymaker or how that scientific decision needed to be weighed against other potential costs and hazards," said Molly Diggory, a civil engineering student and paper co-author who focused on earthquake damage to water heaters in her part of the study. "It really opened up my thought process to anticipate this type of real-world analysis."The students also learned that "most natural hazard mitigation policies are derived without cost-benefit analysis" Stein said. The complicated decision of whether to build a seawall to protect against a tsunami, for example, requires input from multiple scientific and economic studies, and most agencies aren't equipped to take that multidisciplinary approach, he said.Stein hopes the paper will encourage other classes to take a deeper look at real-world natural hazards policy."Our results aren't surprising, since as far as we know no water heaters in Illinois have ever been seriously damaged by an earthquake. But what's important is the way the class tackled this complicated issue," he said."Typical natural hazards classes show great pictures of destroyed buildings and lava flowing and so on, but don't encourage the students to ask the really interesting but hard policy questions," Stein continued. "Students can handle tough problems, and we should teach them do that." | Earthquakes | 2,016 |
February 9, 2016 | https://www.sciencedaily.com/releases/2016/02/160209132039.htm | Mysterious Menominee crack is unusual geological pop-up feature | Seismologists studying a massive crack in the ground that appeared north of Menominee, Michigan in 2010 now think they know what the unusual feature might be. But as they explain in their study published this week in the journal | A team of scientists led by Wayne Pennington of Michigan Technological University says that the crack, which lies along the crest of a two-meter-high ridge that appeared at the same time, is probably a "pop-up" feature. Pop-ups occur in places where shallowly-buried rock layers spring upward after having been weighed down by rock or ice. Pop-ups--sometimes called "A-tents" for their shape--may develop in places where the earth rebounds upward after an overlying glacier shrinks away, or when rock overburden is removed in a quarry.However, the last glaciers retreated from Menominee 11,000 years ago--and there isn't any quarrying in the area."One of our reasons for publishing this was that in our search of the literature we could find no other mention of modern pop-ups that didn't occur at something like the base of a quarry, where people had removed massive amounts of rock earlier," Pennington explained. "As far as we can tell, this is a one-of-a-kind event."Residents near Menominee heard a loud noise and shaking in the early morning of October 4, 2010, and soon discovered the crack when they went into the nearby woods to clean up the debris left from removing a big double-trunked white pine tree a few days earlier. The crack split the ground for 110 meters, and was as deep as 1.7 meters in some places. Tree trunks tilted at precarious angles on either side of the fracture.Pennington went to visit the site on his way back home from a scientific conference, he recalled. He paced off some measurements in his dress shoes and collected some GPS data with his phone. "I was completely blown away by it, because it wasn't what I was expecting when I saw it," he recalled. "It wasn't like anything I had seen before."Although the crack was the most dramatic feature, Pennington was intrigued by the new ridge underneath it. "I kept trying to think of ways that there could have been an uplift from a thrusting earthquake or something, but anything like that requires such a huge amount of displacement in order to produce that amount of crustal shortening, that nothing made sense."He shared the photos and data with his colleagues, until Stanford University geophysicist Norm Sleep pointed out that the feature formed from a shallow-buried layer of limestone, and looked like a pop-up. "This made perfect sense to us," Pennington said, "except for what caused it. And that then became the puzzle."The researchers needed to get a better look at the rock underneath the ridge to confirm that it was a pop-up, so they turned to a technique called seismic refraction. The technique measures the speed of seismic waves as they travel within layers of the earth, as determined at different distances from the seismic source. In this case, the seismologists used a sledgehammer to strike a large metal ball lying on the ground, and captured the resulting seismic waves.In broken rock, the waves travel faster as they move parallel to cracks in the rock, and slower when they move perpendicular to the cracks and have to travel across the fractures. The scientists found a pattern of refraction speeds that seemed to be consistent with the intense bending and then fracturing of the brittle limestone of a pop-up feature.But what caused the pop-up to...pop-up? Without the usual suspects in play, Pennington and his colleagues had to do a little detective work. The limestone in the area may have been stressed almost to the point of cracking when the last glaciers retreated, they say. The recent removal of the double-trunked pine, which may have weighed as much as 2000 kilograms--over two tons--could have been the final straw, allowing the rock to bend upward when that weight was removed."There's a 60% chance that this explanation we provide is the right one," Pennington noted. "But since we haven't seen this kind of thing elsewhere, and the tree is such a small effect, we wonder if there might be something else."The seismologists studied aerial photos of the region to see how soil has been removed in the past 50 years from road work and a re-design of the area's drainage system. These changes might have channeled more rainwater below the surface, potentially weakening the rock as it froze and thawed, the scientists suggest.Pennington said "no one should be losing sleep" over the strange feature, which technically counted as the first natural earthquake in Michigan's Upper Peninsula--measuring less than magnitude 1."It may be a one-of-a kind phenomenon," he said. "But if it happens again, we'll be all over it, trying to figure it out." | Earthquakes | 2,016 |
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