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Full-Text Articles in Physical Sciences and Mathematics
Seismic Azimuthal Anisotropy Beneath A Fast Moving Ancient Continent: Constraints From Shear Wave Splitting Analysis In Australia, Kailun Ba, Stephen S. Gao, Jianguo Song, Kelly H. Liu
Seismic Azimuthal Anisotropy Beneath A Fast Moving Ancient Continent: Constraints From Shear Wave Splitting Analysis In Australia, Kailun Ba, Stephen S. Gao, Jianguo Song, Kelly H. Liu
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
Seismic Azimuthal Anisotropy Beneath Australia is Investigated using Splitting of the Teleseismic PKS, SKKS, and SKS Phases to Delineate Asthenospheric Flow and Lithospheric Deformation Beneath One of the Oldest and Fast-Moving Continents on Earth. in Total 511 Pairs of High-Quality Splitting Parameters Were Observed at 116 Seismic Stations. Unlike Other Stable Continental Areas in Africa, East Asia, and North America, Where Spatially Consistent Splitting Parameters Dominate, the Fast Orientations and Splitting Times Observed in Australia Show a Complex Pattern, with a Slightly Smaller Than Normal Average Splitting Time of 0.85 ± 0.33 S. on the North Australian Craton, the Fast …
Laterally Heterogeneous Seismic Anisotropy Investigated By Shear Wave Splitting Analyses, Yan Jia
Laterally Heterogeneous Seismic Anisotropy Investigated By Shear Wave Splitting Analyses, Yan Jia
Doctoral Dissertations
"Numerous geophysical studies suggest that seismic anisotropy is a nearly ubiquitous property of the Earth’s crust and upper mantle. In this study, we utilize the shear wave splitting technique to investigate the piercing-point-dependent azimuthal anisotropy beneath the northeastern edge of the Sichuan Basin in central China, and the spatial and temporal variations of anisotropy near the 2019 M7.1 Ridgecrest earthquake in California, respectively. A clear back azimuthal dependence of the splitting parameters and the lack of a 90° or 180° periodicity of azimuthal variation in the observed fast orientations provide strong evidence for the existence of piercing-point-dependent anisotropy beneath the …
Direct P-Wave Anisotropy Measurements At Homestake Mine: Implications For Wave Propagation In Continental Crust, James Atterholt, Sarah J. Brownlee, Gary L. Pavlis
Direct P-Wave Anisotropy Measurements At Homestake Mine: Implications For Wave Propagation In Continental Crust, James Atterholt, Sarah J. Brownlee, Gary L. Pavlis
Environmental Science and Geology Faculty Research Publications
We measured anisotropic seismic properties of schists of the Homestake Formation located at a depth of 1478 m in the Sanford Underground Research Facility (SURF) in the Black Hills of South Dakota, USA. We deployed a 24-element linear array of three-component geophones in an area in the Homestake Mine called 19-ledge. An airless jackhammer source was used to shoot two profiles: (1) a walkaway survey to appraise any distance dependence and (2) a fan shot profile to measure variations with azimuth. Slowness estimates from the fan shot profile show a statistically significant deviation with azimuth with the expected 180° variation …
Characteristics Of Deep Crustal Seismic Anisotropy From A Compilation Of Rock Elasticity Tensors And Their Expression In Receiver Functions, Sarah J. Brownlee, Vera Schulte-Pelkum, Anissha Raju, Kevin Mahan, Cailey Condit, Omero Felipe Orlandini
Characteristics Of Deep Crustal Seismic Anisotropy From A Compilation Of Rock Elasticity Tensors And Their Expression In Receiver Functions, Sarah J. Brownlee, Vera Schulte-Pelkum, Anissha Raju, Kevin Mahan, Cailey Condit, Omero Felipe Orlandini
Environmental Science and Geology Faculty Research Publications
Rocks in the continental crust are long lived and have the potential to record a wide span of tectonic history in rock fabric. Mapping rock fabric in situ at depth requires the application of seismic methods. Below depths of microcrack closure seismic anisotropy presumably reflects the shape and crystallographic preferred orientations influenced by deformation processes. Interpretation of seismic observables relevant for anisotropy requires assumptions on the symmetry and orientation of the bulk elastic tensor. We compare commonly made assumptions against a compilation of 95 bulk elastic tensors from laboratory measurements, including electron backscatter diffraction and ultrasound, on crustal rocks. The …
Seismic Anisotropy As A Function Of Mineralogy And Rock Type In Chester Gneiss Dome, Southeast Vermont, Brittany Watling
Seismic Anisotropy As A Function Of Mineralogy And Rock Type In Chester Gneiss Dome, Southeast Vermont, Brittany Watling
Wayne State University Theses
Our knowledge of composition and structure in middle and lower crustal rocks is limited due to restricted accessibility, and thus comes mainly from studies of seismic velocities. But isotropic seismic velocities are not sufficient to distinguish between the many possible rock types in the middle and lower crust. Seismic anisotropy is the directional dependence of seismic velocity, and may provide further constraints on mineralogy and rock type. This study is focused on characterizing the seismic anisotropy of rocks from the Chester dome in southeast Vermont. We have simplified the Chester dome rock types into four groups based on rock type …
Inferring The Oriented Elastic Tensor From Surface Wave Observations: Preliminary Application Across The Western United States, Jiayi Xie, Michael H. Ritzwoller, S. J. Brownlee, B. R. Hacker
Inferring The Oriented Elastic Tensor From Surface Wave Observations: Preliminary Application Across The Western United States, Jiayi Xie, Michael H. Ritzwoller, S. J. Brownlee, B. R. Hacker
Environmental Science and Geology Faculty Research Publications
Radial and azimuthal anisotropy in seismic wave speeds have long been observed using surface waves and are believed to be controlled by deformation within the Earth’s crust and uppermost mantle. Although radial and azimuthal anisotropy reflect important aspects of anisotropic media, few studies have tried to interpret them jointly. We describe a method of inversion that interprets simultaneous observations of radial and azimuthal anisotropy under the assumption of a hexagonally symmetric elastic tensor with a tilted symmetry axis defined by dip and strike angles. We show that observations of radial anisotropy and the 2ψ component of azimuthal anisotropy for Rayleigh …
Predicted Velocity And Density Structure Of The Exhuming Papua New Guinea Ultrahigh‐Pressure Terrane, Sarah J. Brownlee, Bradley R. Hacker, Matthew Salisbury, Gareth Seward, Timothy A. Little, Suzanne A. Baldwin, Geoffrey A. Abers
Predicted Velocity And Density Structure Of The Exhuming Papua New Guinea Ultrahigh‐Pressure Terrane, Sarah J. Brownlee, Bradley R. Hacker, Matthew Salisbury, Gareth Seward, Timothy A. Little, Suzanne A. Baldwin, Geoffrey A. Abers
Environmental Science and Geology Faculty Research Publications
New electron backscatter diffraction measurements show that the Papua New Guinea (PNG) ultrahigh‐pressure (UHP) terrane is dominated by rocks with weakly oriented quartz and feldspar and less abundant strongly oriented hornblende, clinopyroxene, and mica. Velocities measured at high pressures (600 MPa) show that VP is 5.8–6.3 km/s for gneiss samples, 6.5–7.7 km/s for amphibolite, and 7.7–8.2 km/s for eclogite and VS is 3.4–3.9 km/s for gneiss, 4.0–4.4 km/s for amphibolite, and 4.5–4.6 km/s for eclogite. Velocities and anisotropies calculated from mineral crystal preferred orientations (CPOs) are equivalent to within 5% of the measured values. The highest seismic anisotropy …
Significant Seismic Anisotropy Beneath The Southern Lhasa Terrane, Tibetan Plateau, Stephen S. Gao, Kelly H. Liu
Significant Seismic Anisotropy Beneath The Southern Lhasa Terrane, Tibetan Plateau, Stephen S. Gao, Kelly H. Liu
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
Shear wave splitting measurements using teleseismic PKS, SKKS, and SKS phases recorded by station LSA on the southern part of the Lhasa Terrane of the Tibetan Plateau reveal significant azimuthal anisotropy with a splitting time of up to 1.5 s, a conclusion that is contradictory to previous studies which suggested isotropy or weak anisotropy. In addition, systematic variations of the splitting parameters (fast polarization direction and splitting time) with the arriving azimuth of the seismic ray path are observed, suggesting a model of anisotropy that is more complicated than a single layer with horizontal axis of symmetry. The measurements are …
Evidence For Small-Scale Mantle Convection In The Upper Mantle Beneath The Baikal Rift Zone, Stephen S. Gao, Kelly H. Liu, Paul M. Davis, Philip D. Slack, Yuliy A. Zorin, Valentina V. Mordvinova, Vladimir M. Kozhevnikov
Evidence For Small-Scale Mantle Convection In The Upper Mantle Beneath The Baikal Rift Zone, Stephen S. Gao, Kelly H. Liu, Paul M. Davis, Philip D. Slack, Yuliy A. Zorin, Valentina V. Mordvinova, Vladimir M. Kozhevnikov
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
Inversion of teleseismic P wave travel time residuals collected along a 1280-km-long profile traversing the Baikal rift zone (BRZ) reveals the existence of an upwarped lithosphere/asthenosphere interface, which causes a travel time delay of about 1 s at the rift axis ("central high"). An area with early arrivals relative to the stable Siberian platform of up to 0.5 s is observed on each side of the rift, about 200 km from the rift axis ("flank lows"). While the location of the central high is approximately fixed in the vicinity of the rift axis, those of the flank lows vary as …