The Experts below are selected from a list of 27750 Experts worldwide ranked by ideXlab platform
Laurence J Jacobs - One of the best experts on this subject based on the ideXlab platform.
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diffraction attenuation and source corrections for nonlinear Rayleigh Wave ultrasonic measurements
Ultrasonics, 2015Co-Authors: David Torello, Sebastian Thiele, Kathryn H Matlack, Jianmin Qu, Laurence J JacobsAbstract:Abstract This research considers the effects of diffraction, attenuation, and the nonlinearity of generating sources on measurements of nonlinear ultrasonic Rayleigh Wave propagation. A new theoretical framework for correcting measurements made with air-coupled and contact piezoelectric receivers for the aforementioned effects is provided based on analytical models and experimental considerations. A method for extracting the nonlinearity parameter β 11 is proposed based on a nonlinear least squares curve-fitting algorithm that is tailored for Rayleigh Wave measurements. Quantitative experiments are conducted to confirm the predictions for the nonlinearity of the piezoelectric source and to demonstrate the effectiveness of the curve-fitting procedure. These experiments are conducted on aluminum 2024 and 7075 specimens and a β 11 7075 / β 11 2024 measure of 1.363 agrees well with previous literature and earlier work. The proposed work is also applied to a set of 2205 duplex stainless steel specimens that underwent various degrees of heat-treatment over 24 h, and the results improve upon conclusions drawn from previous analysis.
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relationship between Rayleigh Wave polarization and state of stress
Ultrasonics, 2006Co-Authors: Michael Junge, Laurence J JacobsAbstract:This research develops an analytical model (using Stroh's formalism) to predict the affect of applied stress on the Wave speed and the polarization of Rayleigh surface Waves. Simulation results are then used to demonstrate that the polarization of a Rayleigh Wave (which is reference-free) could be more sensitive than Wave speed as an indicator of the state of stress.
Brandon Schmandt - One of the best experts on this subject based on the ideXlab platform.
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Upper crustal azimuthal anisotropy across the contiguous U.S. determined by Rayleigh Wave ellipticity
Geophysical Research Letters, 2014Co-Authors: Fan Chi Lin, Brandon SchmandtAbstract:Constraints on upper crustal seismic anisotropy provide insight into the local stress orientation and structural fabric, but such constraints are scarce except in areas with dense recordings of local seismicity. We investigate directionally dependent Rayleigh Wave ellipticity, or Rayleigh Wave H/V (horizontal to vertical) amplitude ratios, between 8 and 20 s period across USArray to infer azimuthal anisotropy in the upper crust across the contiguous U.S. To determine the H/V ratios, we use all available multicomponent ambient noise cross correlations between all USArray stations operating between 2007 and 2013. In many locations, the observed H/V ratios are clearly back azimuth dependent with a 180° periodicity, which allows the fast directions and amplitudes of upper crustal anisotropy to be determined. The observed patterns of anisotropy correlate well with both near-surface geological features (e.g., the Intermountain Seismic Belt and Appalachian-Ouachita collision belt) and a previous stress model.
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3 d crustal structure of the western united states application of Rayleigh Wave ellipticity extracted from noise cross correlations
Geophysical Journal International, 2014Co-Authors: Fan Chi Lin, Victor C Tsai, Brandon SchmandtAbstract: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.
Frederic Deschamps - One of the best experts on this subject based on the ideXlab platform.
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azimuthal anisotropy of Rayleigh Wave phase velocities in the east central united states
Geophysical Journal International, 2008Co-Authors: Frederic Deschamps, Sergei Lebedev, Thomas Meier, Jeannot TrampertAbstract:SUMMARY We explore the Rayleigh-Wave phase velocity structure of the east-central US in a broad period range (10‐200 s). Using a recent implementation of the two-stations method, we first measure interstation dispersion curves of Rayleigh-Wave phase velocities along 60 paths. We then invert our collection of dispersion curves for isotropic and azimuthally anisotropic (2� and 4� ) phase‐velocity maps. The inversion is performed by a damped, smoothed LSQR, and the output model is parametrized on a triangular grid of knots with a 140 km grid spacing. Using the isotropic component of the phase velocity maps to constrain regional variations in shear velocity and Moho-depth, we observe that over the upper-middle crust depth range (z 1 per cent), and the azimuth of the fast-propagation direction is uniform over the entire region and equal to 54 ◦ . Our results suggest that azimuthal anisotropy beneath the east-central US is vertically distributed in three distinct layers, with a different geodynamic origin for each of them.
Fan Chi Lin - One of the best experts on this subject based on the ideXlab platform.
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Upper crustal azimuthal anisotropy across the contiguous U.S. determined by Rayleigh Wave ellipticity
Geophysical Research Letters, 2014Co-Authors: Fan Chi Lin, Brandon SchmandtAbstract:Constraints on upper crustal seismic anisotropy provide insight into the local stress orientation and structural fabric, but such constraints are scarce except in areas with dense recordings of local seismicity. We investigate directionally dependent Rayleigh Wave ellipticity, or Rayleigh Wave H/V (horizontal to vertical) amplitude ratios, between 8 and 20 s period across USArray to infer azimuthal anisotropy in the upper crust across the contiguous U.S. To determine the H/V ratios, we use all available multicomponent ambient noise cross correlations between all USArray stations operating between 2007 and 2013. In many locations, the observed H/V ratios are clearly back azimuth dependent with a 180° periodicity, which allows the fast directions and amplitudes of upper crustal anisotropy to be determined. The observed patterns of anisotropy correlate well with both near-surface geological features (e.g., the Intermountain Seismic Belt and Appalachian-Ouachita collision belt) and a previous stress model.
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3 d crustal structure of the western united states application of Rayleigh Wave ellipticity extracted from noise cross correlations
Geophysical Journal International, 2014Co-Authors: Fan Chi Lin, Victor C Tsai, Brandon SchmandtAbstract: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.
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ambient noise Rayleigh Wave tomography of new zealand
AGUFM, 2007Co-Authors: Fan Chi Lin, Michael H Ritzwoller, John Townend, Stephen Bannister, Martha K SavageAbstract:SUMMARY We present the first New Zealand-wide study of surface Wave dispersion, using ambient noise observed at 42 broad-band stations in the national seismic network (GeoNet) and the Global Seismic Network (GSN). Year-long vertical-component time-series recorded between 2005 April 1 and 2006 March 31 have been correlated with one another to yield estimated fundamental mode Rayleigh Wave Green’s functions. We filter these Green’s functions to compute Rayleigh Wave group dispersion curves at periods of 5‐50 s, using a phase-matched filter, frequency‐time analysis technique. The uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3-month stacks. After selecting the highest quality dispersion curve measurements, we compute group velocity maps from 7 to 25 s period. These maps, and 1-D shear Wave velocity models at four selected locations, exhibit clear correlations with major geological structures, including the Taranaki and Canterbury Basins, the Hikurangi accretionary prism, and previously reported basement terrane boundaries.
Hiroshi Munekane - One of the best experts on this subject based on the ideXlab platform.
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detection and modeling of Rayleigh Wave induced patterns in the ionosphere
Journal of Geophysical Research, 2011Co-Authors: Lucie Rolland, Philippe Lognonné, Hiroshi MunekaneAbstract:[1] Global Positioning System (GPS) allows the detection of ionospheric disturbances associated with the vertical displacements of most of the major shallow seismic events. We describe a method to model the time and space distributions of Rayleigh Wave induced total electron content (TEC) patterns detected by a dense GPS array. We highlight the conditions for which a part of the ionospheric pattern can be directly measured, at teleseismic distance and above the epicenter. In particular, a satellite elevation angle lower than 40° is a favorable condition to detect Rayleigh Wave induced ionospheric Waves. The coupling between the solid Earth and its atmosphere is modeled by computing the normal modes of the solid Earth–atmosphere system. We show the dependency of the coupling efficiency on various atmospheric conditions. By summation of the normal modes we model the atmospheric perturbation triggered by a given earthquake. This shows that a part of the observation is a Rayleigh-induced radiation pattern and therefore characteristic of the seismic rupture. Through atmosphere-ionosphere coupling, we model the ionospheric perturbation. After the description of the local geomagnetic field anisotropic effects, we show how the observation geometry is strongly affecting the radiation pattern. This study deals with the related data for two earthquakes with far-field and near-field observations using the Japanese GPS network GEONET: after the 12 May 2008 Wenchuan earthquake (China) and after the 25 September 2003 Tokachi-Oki earthquake (Japan), respectively. Waveforms and patterns are compared with the observed TEC perturbations, providing a new step toward the use of ionospheric data in seismological applications.
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Detection and modeling of Rayleigh Wave induced patterns in the ionosphere
Journal of Geophysical Research Space Physics, 2011Co-Authors: Lucie Rolland, Philippe Lognonné, Hiroshi MunekaneAbstract:Global Positioning System (GPS) allows the detection of ionospheric disturbances associated with the vertical displacements of most of the major shallow seismic events. We describe a method to model the time and space distributions of Rayleigh Wave induced total electron content (TEC) patterns detected by a dense GPS array. We highlight the conditions for which a part of the ionospheric pattern can be directly measured, at teleseismic distance and above the epicenter. In particular, a satellite elevation angle lower than 40 degrees is a favorable condition to detect Rayleigh Wave induced ionospheric Waves. The coupling between the solid Earth and its atmosphere is modeled by computing the normal modes of the solid Earth-atmosphere system. We show the dependency of the coupling efficiency on various atmospheric conditions. By summation of the normal modes we model the atmospheric perturbation triggered by a given earthquake. This shows that a part of the observation is a Rayleigh-induced radiation pattern and therefore characteristic of the seismic rupture. Through atmosphere-ionosphere coupling, we model the ionospheric perturbation. After the description of the local geomagnetic field anisotropic effects, we show how the observation geometry is strongly affecting the radiation pattern. This study deals with the related data for two earthquakes with far-field and near-field observations using the Japanese GPS network GEONET: after the 12 May 2008 Wenchuan earthquake (China) and after the 25 September 2003 Tokachi-Oki earthquake (Japan), respectively. Waveforms and patterns are compared with the observed TEC perturbations, providing a new step toward the use of ionospheric data in seismological applications.
