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News Article | December 14, 2016
Site: www.eurekalert.org

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 Geophysical Research Letters.


News Article | December 14, 2016
Site: www.rdmag.com

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 Geophysical Research Letters.


News Article | December 14, 2016
Site: www.treehugger.com

In recent years we've seen a few tech developments that aim to crowdsource earthquake detection and early warning systems. It's known that only a few seconds' warning -- enough time for someone to seek cover or stop using dangerous machinery -- can have a life-saving effect. Smartphones are the ideal crowdsourcing instrument. Millions of people have them with at all times and they already come outfitted with the necessary tools to detect and measure ground vibrations. Researchers at University of California Berkeley developed the MyShake app that was released in February of this year to take advantage of smartphones' sensors and built-in instruments. The free Android app uses the phone's accelerometer and GPS to measure the strength of vibrations and where they're being felt. Since its release, 220,000 people have downloaded the app and at any given time close to 10,000 of those are active and ready to detect motion -- turned on, lying on a horizontal surface and connected to WiFi. Since February, 400 earthquakes have been detected in places like Chile, Japan, China, California and, notably, the fracking fields of Oklahoma. The app measure ground motion and then sends the information to Berkeley Seismological Laboratory for analysis. Right now, the data is collected and used to show app users where recent earthquakes have occurred, but the goal is to start issuing alerts when initial movements are felt. The researchers say that the data they've collected over the past few months has proven that phones are sensitive enough and there are enough users in earthquake prone areas to detect those first vibrations. The app was able to detect the first seismic waves that arrive -- the P waves, which are less destructive -- which could give them enough time to issue warnings before the more dangerous S waves 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," said UC Berkeley developer and graduate student Qingkai Kong. A new version of the app was just released that does issue notifications of nearby earthquakes but not early warnings. The app can detect an earthquake as small as a 2.5 magnitude where there is a good density of phones. In the trial period, the greatest number of phones to detect a quake was 103 that picked up the vibrations from the 5.2 magnitude quake that hit Borrego Springs, Ca. in June. The largest quake detected was a 7.8 magnitude one in Ecuador in April felt by two phones over a hundred miles from the epicenter. The leader in amount of earthquakes though was Oklahoma where hundreds of quakes were set off from hydraulic fracking.


News Article | March 4, 2016
Site: news.yahoo.com

NEW YORK (Thomson Reuters Foundation) - Smartphones could become the makeshift quake detectors of the future, thanks to a new app launched Friday designed to track tremors and potentially save the lives of its users. MyShake, available on Android, links users to become an all-in-one earthquake warning system; it records quake-type rumblings, ties a critical number of users to a location, and could eventually provide a countdown to the start of shaking. Its inventors say the app, released by the University of California, Berkeley, could give early warning of a quake to populations without their own seismological instruments. "MyShake cannot replace traditional seismic networks like those run by the U.S. Geological Survey," said Richard Allen, leader of the app project and director of the Berkeley Seismological Laboratory. "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." Earthquake-prone countries in the developing world with poor ground-based seismic network or early warning systems include Nepal, Peru, Pakistan, Turkmenistan and Iran, he said. The algorithm behind MyShake, developed by a handful of Silicon Valley programmers, relies on the same technology smartphone gamers depend on to sense the phone's orientation, known as the accelerometer, in order to measure movement caused by quakes. What smartphones lack in sensitivity - they can only record earthquakes above magnitude 5 within 10 kilometers (6 miles) - they make up for in ubiquity. Currently, 300 smartphones equipped with MyShake within a 110-km square area are enough to estimate a quake's location, magnitude and origin time. There were some 3.4 billion smartphone subscriptions worldwide in 2015, according to the Ericsson Mobility Report, so the app's creators hope to build a seismic network covering the globe. "We want to make this a killer app, where you put it on your phone and allow us to use your accelerometer, and we will deliver earthquake early warning," Allen said. Sophisticated early-warning systems can warn of coming quakes as much as a few minutes before they begin, but cannot stop them causing death and destruction on a large scale. Nepal is still rebuilding after two separate earthquakes in April and May 2015 that killed 9,000 people, injured more than 22,000 and damaged or destroyed nearly 900,000 houses.


News Article | December 15, 2016
Site: www.techtimes.com

Northwestern University researchers have answered the question why earthquakes happen in clusters. The clusters are explained as localized seismic events like quakes happening in quick sequences of short time spans such as days, weeks, or months. In a computer model, the researchers noted that earthquake faults have a role on it as they keep a better memory of the latest event paving way for a recurrence. "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 senior author of the study and Professor of Geological Sciences at the Weinberg College of Arts and Sciences. The research paper S44B­08: "Are Earthquake Clusters/Supercycles Real or Random?" will be presented on Thursday, Dec. 15, at the American Geophysical Union (AGU) meeting in San Francisco by Leah Salditch, the lead author. The model shows swarms or clusters happen on faults with long-term memory. This means even after a bigger earthquake, chances of another one happening are quite high. That is because an earthquake may not release all the pressure at the fault in one event and the left over strain can trigger another one. The 1906 earthquake in San Francisco was a trend setter in this regard. Seismologists started predicting possible quakes on the basis of a fault's memory of the previous earthquake irrespective of the past quakes there. The premise of fault's memory in forecasting future earthquakes and hazard mapping goes a long way in planning for buildings that can resist earthquakes with appropriate capacities. Salditch, a graduate student at Stein's research, threw more light into the phenomenon and said there had been earthquakes having short time spans separating them punctuated with longer times of lull. San Andrea's clusters had a 50 years gap in big earthquakes while clusters were separated by hundreds of years. Clusters on the fault at Cascadia near Oregon, British Columbia, Washington and the Dead Sea fault are also possible examples. One of the authors of the study, Edward M. Brooks, said the study is valuable in forecasting future earthquakes by tracking the last incident. Meanwhile, the University of California, Berkeley's worldwide network of smartphone earthquake detectors recorded nearly 400 earthquakes since the MyShake app was released in February. Among the spots, the most active seismic ones were Oklahoma fracking fields. The ground motion is measured by the Android app using a smart phone's motion sensors and the data is sent to the Berkeley Seismological Laboratory for analysis. The alerts give users the warning time to save or switch off damageable equipment. Already, 200,000 people have downloaded the app whose new version was out on Dec. 14 with options for notifications of quakes nearby. Richard Allen, UC Berkeley professor of earth sciences and the project leader said the technology would make alerts faster to improve real-time detection with MyShake. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.


News Article | September 26, 2016
Site: www.rdmag.com

A new look 100 miles beneath a massive tectonic plate as it dives under North America has helped clarify the subduction process that generates earthquakes, volcanoes and the rise of the Cascade Range in the Pacific Northwest. The largest array of seismometers ever deployed on the seafloor, coupled with hundreds of others operating in the continental U.S., has enabled UC Berkeley researchers to essentially create CT scans of the Juan de Fuca plate and part of the earth’s mantle directly below it. The plate, about the size of the state of Michigan, is grinding under the continent along an 800-mile swath that runs from Northern California to Vancouver Island, known as the Cascadia subduction zone. The 3-D imaging process, known as seismic tomography, has revealed with unprecedented clarity a huge, buoyant, sausage-shaped region of the upper mantle, or asthenosphere, pressing up on the oceanic plate. The imaging casts new light on the competing hypotheses about the drivers of plate tectonics, a dynamic earth process that has been studied for more than 50 years but is still poorly understood. Different evidence has led to three different plate movement scenarios: either the plates are pushed from mid-ocean ridges; or they are pulled from their subducting slabs; or their movement is driven by the drag of the viscous mantle material that lies directly below. The new research suggests that the third scenario does not apply to the Cascadia subduction zone. Rather, it reveals that a distinct, thin — and difficult to observe — layer separates the plate from the mantle beneath, at least in the Cascadia subduction zone. The layer acts as a kind of berm that the plate rolls over before descending beneath the continent, says UC Berkeley seismologist Richard Allen, leader of the research and co-author of a paper appearing in the Sept. 23 edition of the journal Science. “What we observe is an accumulation of low-viscosity material between the plate and the mantle. Its composition acts as a lubricant, and decouples the plate’s movement from the mantle below it,” explains Allen, who is director of the Berkeley Seismological Laboratory and professor and chair of Earth and Planetary Science at Berkeley. The plates may move independently of the mantle below, he adds. The finding, he says, will help refine models of plate tectonic dynamics, aiding the long-range effort to understand the connection between tectonics and earthquakes. “It is the motion of the plates that causes earthquakes,” Allen says. “Models like this help us understand that linkage so we can be better informed of the coastal hazards. “First though, we need to learn if what we find here is typical of subduction zones across the planet, or if it is unique for some reason.” Japan has recently deployed a massive seafloor seismic network to study subduction and earthquakes. Allen hopes to next apply the tomography strategy there. Alaska also beckons. Lead author on the Science paper is William Hawley, a graduate student in Allen’s lab. “Plate tectonics is the most fundamental concept explaining the formation of features we see on the earth’s surface,” Hawley says, “but despite the fact that the concept is simple, we still do not know exactly why or how it operates. “If the asthenosphere acts as a lubricant for tectonic plate movement throughout the planet, it will really change our long-term models of the process” — dynamic changes that occur over a 100 million years. “Modelers will have to take this lubricating layer into account because it changes the way the mantle and the plates talk to each other.” Seismic tomography generates 3-D images of the earth’s interior by measuring how differences in shape, density, rock type and temperature affect the path, speed and amplitude of seismic waves traveling through the planet from an earthquake. Much as in CT scans, computers process differences in energy measured at the receiving end to infer interior 3-D detail. CT scans use X-rays as the energy source, while seismic tomography measures energy from seismic waves. A dense array of seismometers directly over the region of interest yields the best images and provides the highest resolution of the structures, which can then inform models of the process. This study used the data from the largest scale ocean-floor deployment to complement the onshore data already available. Together, they generated the best images of the region to date. The four-year seafloor research effort was made possible by the National Science Foundation’s ambitious $20 million Cascadia Initiative. The NSF aimed to spur greater understanding of plate structure, subduction processes, earthquakes and volcanism by deploying seismometers at 120 sites on the ocean floor, arrayed throughout the 95,000-square-mile Juan de Fuca plate. Over the four years, the offshore and onshore seismometer array measured thousands of earthquakes throughout the planet, ranging from magnitudes of 5 to about 9 on the Richter scale. The study examined a subset of 321 quakes with magnitudes between about 6 and 7.5.


Lekic V.,Berkeley Seismological Laboratory | Lekic V.,Brown University | Romanowicz B.,Berkeley Seismological Laboratory
Earth and Planetary Science Letters | Year: 2011

Global mantle tomography can be improved through better use of data and application of more accurate wave propagation methods. However, few techniques have been developed for objective validation and exploration of the resulting tomographic models. We show that cluster analysis can be used to validate and explore the salient features across such models. We present a cluster analysis of a global upper mantle radially anisotropic model SEMum developed using full waveform tomography and the Spectral Element Method. Applied to SEMum down to 350 km depth, the cluster analysis reveals that absolute shear wave velocity (Vs) depth profiles naturally group into families that correspond with known surface tectonics. This allows us to construct a global tectonic regionalization based solely on tomography, without the help of any a priori information. We find that the profiles of stable platforms and shields consistently exhibit a mid-lithospheric low velocity zone (LVZ) between 80 and 130. km depth, while the asthenosphere is found at depths greater than 250. km in both regions. This global intra-continental-lithosphere low velocity zone agrees with recent receiver function studies and regional tomographic studies. Furthermore, we identify an anomalous oceanic region characterized by slow shear wave speeds at depths below 150. km. Hotspots are found preferentially in the vicinity of this anomalous region. In the Pacific Ocean, where plate velocities are largest, these regions have elongated shapes that align with absolute plate motion, suggesting a relationship between the location of hotspots and small-scale convection in the oceanic upper mantle. © 2011 Elsevier B.V.


News Article | December 18, 2016
Site: www.techtimes.com

Thanks to MyShake – an earthquake detection app released in February – almost 400 earthquakes in the past 10 months have been recorded. According to UC Berkeley officials, they recorded surprisingly higher seismic activities in the fracking fields of Oklahoma. In fact, in 2015, Oklahoma residents experienced tremors 907 times. Since 2008, the region's earthquake activity increased by a factor of 43, which in percentage terms comes to 4,000 percent. According to earthquake researcher and Ph.D. student Pengyun Wang, wastewater fluid injection technologies from fracking fields are contributing to it. With users' data, the MyShake app helped in tracking 395 earthquakes of varying magnitudes and the developers are citing it as the proof of its super efficacy. The Android app was downloaded by 220,000 people. Going by its success, there is a perception that seismic sensitivity of the smartphone accelerometers along with phone density can help in early warning. In terms of operation, the app uses motion detectors in smartphones to measure ground motion with data being sent to the Berkeley Seismological Laboratory for a detailed analysis. A new version was released on Dec.14 and is available at the Google Play Store with options for notifications of recent quakes. "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 and the seismology lab's director. The app was also discussed in a paper by Louis Schreier, who co-wrote a paper that was published in Geophysical Research Letters. Now the researchers are readying a presentation at the American Geophysical Union meeting in San Francisco. Qingkai Kong, the UC Berkeley developer and a graduate student, will present a brief on the app's performance. Allen and Kong, along with colleagues at Deutsche Telekom's Silicon Valley Innovation Center, believe that the app's performance will complement other official networks and can reduce damage and deaths from earthquakes. The app can detect quakes as small as magnitude 2.5 in Richter scale. It differs from other earthquake apps like Quakes, QuakeFeed and Earthquake as they show earthquakes of the past with data taken from the U.S. Geological Survey. In MyShake, when the app developers receive too many notifications from one area, they recognize an earthquake is due and start sending the alerts. One main merit is the app uses very little power and as soon as the seismic activity is sensed, it becomes active and works best when the phone is put on a flat surface like a table. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.


Ford S.R.,Lawrence Livermore National Laboratory | Dreger D.S.,Berkeley Seismological Laboratory | Walter W.R.,Lawrence Livermore National Laboratory
Bulletin of the Seismological Society of America | Year: 2010

Well-resolved moment-tensor solutions reveal information about the sources of seismic waves. In this paper, we introduce a new way of assessing confidence in the regional full moment-tensor inversion via the introduction of the network sensitivity solution (NSS). The NSS takes into account the unique station distribution, frequency band, and signal-to-noise ratio of a given event scenario. The NSS compares both a hypothetical pure source (for example, an explosion or an earthquake) and the actual data with several thousand sets of synthetic data from a uniform distribution of all possible sources. The comparison with a hypothetical pure source provides the theoretically best-constrained source-type distribution for a given set of stations; and with it, one can determine whether further analysis with the data is warranted. The NSS that employs the actual data gives a direct comparison of all other source types with the best-fit source. In this way, one can choose a threshold level of fit in which the solution is comfortably constrained. The method is tested for the well-recorded nuclear test, JUNCTION, at the Nevada Test Site. Sources that fit comparably well to a hypothetical pure explosion recorded with no noise at the JUNCTION data stations have a large volumetric component and are not described well by a double-couple (DC) source. The NSS using the real data from JUNCTION is even more tightly constrained to an explosion because the data contain some energy that precludes fitting with any type of deviatoric source. We also calculate the NSS for the October 2006 North Korea test and a nearby earthquake, where the station coverage is poor and the event magnitude is small. The earthquake solution is very well fit by a DC source, and the best-fit solution to the nuclear test (M w 4.1) is dominantly explosion.


Audet P.,Berkeley Seismological Laboratory | Burgmann R.,Berkeley Seismological Laboratory
Nature Geoscience | Year: 2011

Supercontinents episodically assemble and break up, in association with the closure and opening of ocean basins. During these cycles, continental margins are repeatedly weakened and deformed during subduction, orogeny and rifting, whereas continental cores tend to remain intact. It has therefore been suggested that deformation during supercontinent cycles is controlled by the pre-existing structure of the lithosphere, for example by rheological heterogeneities and mechanical anisotropy that were acquired during past tectonic events. However, observational constraints for this idea have been lacking. Here we present global, high-resolution maps of the lithosphere's effective elastic thickness over the continents-a proxy for the rigidity or long-term strength of the lithosphere-calculated from a comparison of the spectral coherence between topography and gravity anomalies and the flexural response of an equivalent elastic plate to loading. We find that effective elastic thickness is high in Archean cratons, but low in the surrounding Phanerozoic belts. We also estimate the anisotropy in effective elastic thickness, indicative of a directional dependence of lithospheric rigidity, and show that directions of mechanical weakness align with large gradients in effective elastic thickness and with tectonic boundaries. Our findings support the notion that lithospheric rigidity is controlled by pre-existing structure, and that during the supercontinent cycle, strain is concentrated at pre-existing zones of weakness. © 2011 Macmillan Publishers Limited. All rights reserved.

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