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Berkeley, CA, United States

Ford S.R.,Lawrence Livermore National Laboratory | Phillips W.S.,Los Alamos National Laboratory | Walter W.R.,Lawrence Livermore National Laboratory | Pasyanos M.E.,Lawrence Livermore National Laboratory | Dreger D.S.,Berkeley Seismological Laboratory
Pure and Applied Geophysics | Year: 2010

We invert for regional attenuation of the crustal phase Lg in the Yellow Sea/Korean Peninsula (YSKP) using three different amplitude attenuation tomography methods. The first method solves for source, site, and path attenuation. The second method uses a scaling relationship to set the initial source amplitude and interpret the source term after inversion. The third method implements a coda-derived source spectral correction. By comparing methods with slightly different assumptions we are able to make a more realistic assessment of the uncertainties in the resulting attenuation maps than is obtainable through formal error analysis alone. We compare the site, source and path-terms produced by each method and comment on attenuation, which correlates well with tectonic and topographic features in the region. Source terms correlate well with each other and with magnitude. Site terms are similar except for two stations that are located in a region that has the greatest difference in path term, which demonstrates the site/path trade-off. Another region of path term difference has the fewest crossing paths, where the tomography method employing the coda-derived spectral correction may perform more accurately since it is not as susceptible to the source/path trade-off. The Bohai Bay basin, an area of extension, is a region of high attenuation, and regions of low attenuation occur along topographic highs located in the Da-xin-an-ling and Changbai Mountains and Mount Taishan. © 2009 The Author(s).

Ford S.R.,Lawrence Livermore National Laboratory | Walter W.R.,Lawrence Livermore National Laboratory | Dreger D.S.,Berkeley Seismological Laboratory
Bulletin of the Seismological Society of America | Year: 2012

Determining whether a seismic event is an earthquake, explosion, collapse, or something more complex can be done using regional (Δ < 13°) intermediate-period (T > 10 s) full waveform moment tensors down to low magnitudes (M ~ 3:5). The moment tensor results can be improved for sparse station configurations when teleseismic (Δ > 30°) arraybased short period (T < 1 s) P constraints are added. The inclusion of teleseismic-P aids in event discrimination because it samples the lower region of the focal-sphere, a region where intermediateperiod waveforms recorded at the surface have lowsensitivity for shallow event depths. The teleseismic-P constraint is particularly useful in reducing the trade-off between a shal-low explosion and a shallow volume-compensated linear-vector dipole with a vertical axis in compression. This trade-off can complicate discrimination. The teleseismic-P constraint is applied to the source-type analysis of the announced nuclear test of the Democratic People's Republic of Korea on 25 May 2009, resulting in greater con-fidence in a dominantly explosive solution.

Kim A.,Schlumberger | Dreger D.S.,Berkeley Seismological Laboratory | Larsen S.,Lawrence Livermore National Laboratory
Bulletin of the Seismological Society of America | Year: 2010

We performed 3D ground-motion simulations for 10 recent small to moderate earthquakes (Mw 4.1-5.4) in the San Francisco Bay area to evaluate two versions of the USGS 3D velocity model (Brocher, 2005; Jachens et al., 2006; Brocher, 2008). Comparisons were made in terms of modeling phase arrival timing, peak ground-motion amplitudes, and the seismic waveforms. In the simulations we assumed the source parameters reported in the Berkeley Seismological Laboratory (BSL) Moment Tensor Catalog. Broadband seismic data from the Berkeley Digital Seismic Network (BDSN), and strong motion data from the USGS and the California Geological Survey (CGS) strong motion arrays were used in the analysis. The comparison of peak ground velocity (PGV) for both models reveals that both 3D models predict the observed PGV well over four orders of magnitude, and P-and S-wave timing and pseudospectral acceleration (PSA) are well modeled by the 3D structure. While the revised model (model 8.3.0) significantly improved the timing of the first arrival, and the waveform fit is generally good, there remain discrepancies in estimated amplitudes and durations that require improvements to the structure. Nevertheless, from our low-frequency (0.5 Hz) analysis we found that the 3D model is suitable for the simulation of PGV to assess the strong shaking hazard of future large earthquakes, because earthquakes larger than M 6 have PGV carried by waves of 1 to several seconds period.

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.

Yuan H.,Berkeley Seismological Laboratory | French S.,Berkeley Seismological Laboratory | Cupillard P.,Berkeley Seismological Laboratory | Cupillard P.,CNRS Georesources lab | And 3 more authors.
Earth and Planetary Science Letters | Year: 2014

The EarthScope TA deployment has provided dense array coverage throughout the continental US and with it, the opportunity for high resolution 3D seismic velocity imaging of both lithosphere and asthenosphere in the continent. Building upon our previous long-period waveform tomographic modeling in North America, we present a higher resolution 3D isotropic and radially anisotropic shear wave velocity model of the North American lithospheric mantle, constructed tomographically using the spectral element method for wavefield computations and waveform data down to 40 s period. The new model exhibits pronounced spatial correlation between lateral variations in seismic velocity and anisotropy and major tectonic units as defined from surface geology. In the center of the continent, the North American craton exhibits uniformly thick lithosphere down to 200-250 km, while major tectonic sutures of Proterozoic age visible in the surface geology extend down to 100-150 km as relatively narrow zones of distinct radial anisotropy, with Vsv. >. Vsh. Notably, the upper mantle low velocity zone is present everywhere under the craton between 200 and 300 km depth. East of the continental rift margin, the lithosphere is broken up into a series of large, somewhat thinner (150 km) high velocity blocks, which extend laterally 200-300 km offshore into the Atlantic Ocean. Between the craton and these deep-rooted blocks, we find a prominent narrow band of low velocities that roughly follows the southern and eastern Laurentia rift margin and extends into New England. We suggest that the lithosphere along this band of low velocities may be thinned due to the combined effects of repeated rifting processes and northward extension of the hotspot related Bermuda low-velocity channel across the New England region. We propose that the deep rooted high velocity blocks east of the Laurentia margin represent the Proterozoic Gondwanian terranes of pan-African affinity, which were captured during the Rodinia formation but left behind after the opening of the Atlantic Ocean. Our results suggest that recurring episodes of tectonic events that are well exposed at the surface also leave persistent scars in the continental lithosphere mantle, marked by isotropic and radially anisotropic velocity anomalies that reach as deep as 100-150 km. © 2013 Elsevier B.V.

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