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  • 1
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    Coherence‐based approaches for estimating the composition of the seismic wavefield (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract As new techniques exploiting the Earth's ambient seismic noise field are developed and applied, such as for the observation of temporal changes in seismic velocity structure, it is crucial to quantify the precision with which wave‐type measurements can be made. This work uses array data at the Homestake mine in Lead, South Dakota and an array at Sweetwater, Texas to consider two aspects that control this precision: the types of seismic wave contributing to the ambient noise field at microseism frequencies and the effect of array geometry. Both are quantified using measurements of wavefield coherence between stations in combination with Wiener filters. We find a strong seasonal change between body‐wave and surface‐wave content. Regarding the inclusion of underground stations, we quantify the lower limit to which the ambient noise field can be characterized and reproduced; the applications of the Wiener filters are about 4 times more successful in reproducing ambient noise waveforms when underground stations are included in the array, resulting in predictions of seismic timeseries with less than a 1% residual, and are ultimately limited by the geometry and aperture of the array, as well as by temporal variations in the seismic field. We discuss the implications of these results for the geophysics community performing ambient seismic noise studies, as well as for the cancellation of seismic Newtonian gravity noise in ground‐based, sub‐Hz, gravitational‐wave detectors.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Modeling of subglacial hydrological development following rapid supraglacial lake drainage. (2015)
    Wiley
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    Publication Date: 2015-05-15
    Description: The rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the Greenland Ice Sheet over short timescales. The effect of these water pulses on the development of basal hydrological systems is largely unknown. To address this we develop a lake drainage model incorporating both 1) a subglacial radial flux element driven by elastic hydraulic jacking and 2) downstream drainage through a linked channelized and distributed system. Here we present the model and examine whether substantial, efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system. We force the model with field data from a lake drainage site, 70 km from the terminus of Russell Glacier in West Greenland. The model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system. Following lake drainage, channels grow but are not large enough to reduce the water pressure in the surrounding distributed system, unless pre-existing channels are present throughout the domain. Our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface-to-bed connections.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Site amplification, attenuation and scattering from noise correlation amplitudes across a dense array in Long Beach, CA (2015)
    Wiley
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    Publication Date: 2015-02-03
    Description: For accurate seismic hazard evaluation, both the spatial and frequency-dependent variability in the amplitudes of earthquake ground motions is needed. While this information is rarely fully available due to the paucity of relevant seismic data, dense arrays like the 5200 geophone array in Long Beach, California provide the opportunity to study this amplitude variability. Here, we show that ambient noise correlation amplitudes from the Long Beach array can be used to directly determine frequency-dependent site amplification factors. We analyze Rayleigh-wavefield amplitude gradients from ambient noise correlations that are processed so that relative amplitudes satisfy the wave equation and are therefore meaningful. Ultimately, we construct maps of site amplification across Long Beach at frequencies of 0.67, 1.0 and 2.0 Hz. These maps correlate well with local structure, notably the Newport-Inglewood Fault, and also to known velocity structure. Through this process, we also obtain constraints on average attenuation structure and local scattering.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    A model for subglacial flooding through a pre-existing hydrological network during the rapid drainage of supraglacial lakes (2015)
    Wiley
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    Publication Date: 2015-02-15
    Description: Increasingly large numbers of supraglacial lakes form and drain every summer on the Greenland Ice Sheet. Some of these lakes drain rapidly within the timescale of a few hours, and the vertical discharge of water during these events may find a pre-existing film of water potentially within a distributed drainage system of linked cavities. Here, we present a model for subglacial flooding applied specifically to such circumstances. One of many interesting results we find is that water flows in from the far field prior to the arrival of flooding. We systematically evaluate the effect of initial ice/bed opening on the degree of perturbation to the subglacial system. Of particular importance, we find that floods propagate much faster and vertical displacements are much greater for larger openings. For 10 and 1 cm of initial opening, for example, floods travel about 68% and 50% farther than in the fully coupled ice/bed scenario after 2 hours of drainage, respectively. For the same choices of initial opening, the elastostatic displacement at the injection point is about 1.39 and 1.26 times that of the fully coupled scenario. Using the framework with a pre-existing water film results in avoiding the pressure singularity that is inherent to classical hydrofracture models, thus opening an avenue for integrating the likes of our model within continuum subglacial hydrological models. Furthermore, we foresee that the theory presented can be used to potentially infer subglacial hydrological conditions from surface observables.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Seasonality and increasing frequency of Greenland glacial earthquakes (2006)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2006-03-25
    Description: Some glaciers and ice streams periodically lurch forward with sufficient force to generate emissions of elastic waves that are recorded on seismometers worldwide. Such glacial earthquakes on Greenland show a strong seasonality as well as a doubling of their rate of occurrence over the past 5 years. These temporal patterns suggest a link to the hydrological cycle and are indicative of a dynamic glacial response to changing climate conditions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ekstrom, Goran -- Nettles, Meredith -- Tsai, Victor C -- New York, N.Y. -- Science. 2006 Mar 24;311(5768):1756-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA. ekstrom@seismology.harvard.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16556839" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Earthquake in a maze: compressional rupture branching during the 2012 M(w) 8.6 Sumatra earthquake (2012)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2012-07-24
    Description: Seismological observations of the 2012 moment magnitude 8.6 Sumatra earthquake reveal unprecedented complexity of dynamic rupture. The surprisingly large magnitude results from the combination of deep extent, high stress drop, and rupture of multiple faults. Back-projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system, with relatively slow rupture speed. The east-southeast-west-northwest ruptures add a new dimension to the seismotectonics of the Wharton Basin, which was previously thought to be controlled by north-south strike-slip faulting. The rupture turned twice into the compressive quadrant, against the preferred branching direction predicted by dynamic Coulomb stress calculations. Orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure-insensitive strength of the deep oceanic lithosphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Meng, L -- Ampuero, J-P -- Stock, J -- Duputel, Z -- Luo, Y -- Tsai, V C -- New York, N.Y. -- Science. 2012 Aug 10;337(6095):724-6. doi: 10.1126/science.1224030. Epub 2012 Jul 19.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA. lsmeng@gps.caltech.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22821986" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Offshore Southern California Lithospheric Velocity Structure from Noise Cross Correlation Functions (2016)
    Wiley
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    Publication Date: 2016-04-21
    Description: A new shear-wave velocity model offshore southern California is presented that images plate boundary deformation including both thickening and thinning of the crustal and mantle lithosphere at the westernmost edge of the North American continent. The ALBACORE ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, are used to measure ambient noise correlation functions and Rayleigh-wave dispersion curves which are inverted for 3D shear-wave velocities. The resulting velocity model defines the transition from continental lithosphere to oceanic, illuminating the complex history and deformation in the region. A transition to the present-day strike-slip regime between the Pacific and North American Plates resulted in broad deformation and capture of the now 〉200-km-wide continental shelf. Our velocity model suggests the persistence of uppermost mantle volcanic processes associated with East Pacific Rise spreading adjacent to the Patton Escarpment, which marks the former subduction of Farallon Plate underneath North America. The most prominent of these seismic structures is a low-velocity anomaly underlying San Juan Seamount, suggesting ponding of magma at the base of the crust, resulting in thickening and ongoing adjustment of the lithosphere due to the localized loading. The velocity model also provides a robust framework for future earthquake location determinations and ground shaking simulations for risk estimates.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Volcanology. The Yellowstone magmatic system from the mantle plume to the upper crust (2015)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2015-04-25
    Description: The Yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world. An understanding of its properties is key to enhancing our knowledge of volcanic mechanisms and corresponding risk. Using a joint local and teleseismic earthquake P-wave seismic inversion, we revealed a basaltic lower-crustal magma body that provides a magmatic link between the Yellowstone mantle plume and the previously imaged upper-crustal magma reservoir. This lower-crustal magma body has a volume of 46,000 cubic kilometers, ~4.5 times that of the upper-crustal magma reservoir, and contains a melt fraction of ~2%. These estimates are critical to understanding the evolution of bimodal basaltic-rhyolitic volcanism, explaining the magnitude of CO2 discharge, and constraining dynamic models of the magmatic system for volcanic hazard assessment.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Huang, Hsin-Hua -- Lin, Fan-Chi -- Schmandt, Brandon -- Farrell, Jamie -- Smith, Robert B -- Tsai, Victor C -- New York, N.Y. -- Science. 2015 May 15;348(6236):773-6. doi: 10.1126/science.aaa5648. Epub 2015 Apr 23.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA. Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA. hsinhua.huang@utah.edu. ; Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA. ; Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA. ; Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25908659" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    3-D crustal structure of the western United States: application of Rayleigh-wave ellipticity extracted from noise cross-correlations (2014)
    Oxford University Press
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    Publication Date: 2014-06-22
    Description: We present a new 3-D seismic model of the western United States crust derived from a joint inversion of Rayleigh-wave phase velocity and ellipticity measurements using periods from 8 to 100 s. Improved constraints on upper-crustal structure result from use of short-period Rayleigh-wave ellipticity, or Rayleigh-wave H/V (horizontal to vertical) amplitude ratios, measurements determined using multicomponent ambient noise cross-correlations. To retain the amplitude ratio information between vertical and horizontal components, for each station, we perform daily noise pre-processing (temporal normalization and spectrum whitening) simultaneously for all three components. For each station pair, amplitude measurements between cross-correlations of different components (radial–radial, radial–vertical, vertical–radial and vertical–vertical) are then used to determine the Rayleigh-wave H/V ratios at the two station locations. We use all EarthScope/USArray Tranportable Array data available between 2007 January and 2011 June to determine the Rayleigh-wave H/V ratios and their uncertainties at all station locations and construct new Rayleigh-wave H/V ratio maps in the western United States between periods of 8 and 24 s. Combined with previous longer period earthquake Rayleigh-wave H/V ratio measurements and Rayleigh-wave phase velocity measurements from both ambient noise and earthquakes, we invert for a new 3-D crustal and upper-mantle model in the western United States. Correlation between the inverted model and known geological features at all depths suggests good resolution in five crustal layers. Use of short-period Rayleigh-wave H/V ratio measurements based on noise cross-correlation enables resolution of distinct near surface features such as the Columbia River Basalt flows, which overlie a thick sedimentary basin.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
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    Evidence for Fluid Migration During the 2016 Meinong, Taiwan, Aftershock Sequence (2020)
    American Geophysical Union
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    Publication Date: 2020-09-01
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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