Shear wave splitting and mantle flow beneath LA RISTRA

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Read Full Article (file size: 145234 bytes) Cited by GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 12, 1614, doi:10.1029/2002GL016616, 2003 Shear wave splitting and mantle flow beneath LA RISTRA Rengin Gök Dept. of Physics, New Mexico State Univ., USA James F. Ni Dept. of Physics, New Mexico State Univ., USA Michael West Dept. of Physics, New Mexico State Univ., USA Eric Sandvol Dept. of Geological Sciences, Univ. of Missouri, USA David Wilson Dept. of Earth and Environmental Science, New Mexico Institute of Mining and Technology, USA Richard Aster Dept. of Earth and Environmental Science, New Mexico Institute of Mining and Technology, USA W. Scott Baldridge Earth and Environmental Sciences Division, Los Alamos National Laboratory, USA Stephen Grand Dept. of Geological Sciences, Univ. of Texas at Austin, USA Wei Gao Dept. of Geological Sciences, Univ. of Texas at Austin, USA Frederik Tillmann Bullard Laboratories, Cambridge Univ., UK Steve Semken Dine College, USA Abstract Shear-wave splitting parameters (fast polarization direction and delay time) are determined using data from LA RISTRA (Colorado pLAteau RIo Grande Rift/Great Plains Seismic TRAnsect), a deployment of broadband seismometers extending from the Great Plains, across the Rio Grande Rift and the Jemez Lineament, to the Colorado Plateau. Results show that the fast polarization directions are sub-parallel to North American absolute plate motion. The largest deviations from the plate motion are observed within the western edge of the Great Plains and in the interior of the Colorado Plateau where lithospheric anisotropy may be significant. Delay times range from 0.8 to 1.8 seconds with an average value of 1.4 seconds; the largest values are along the Jemez Lineament and the Rio Grande Rift which are underlain by an uppermost mantle low velocity zone extending to depths of ∼200 km. The anisotropy beneath the central part of LA RISTRA shows a remarkably consistent pattern with a mean fast direction of 40° ± 6°. Seismic anisotropy can be explained by differential horizontal motion between the North American lithosphere and westerly to southwesterly flow of the asthenospheric mantle. The approximately N-S fast direction found beneath western Texas is similar to that observed beneath the southern rift and may reflect a different dynamic regime. Received 16 November 2002; accepted 27 March 2003; published 19 June 2003. Index Terms: 7203 Seismology: Body wave propagation; 7218 Seismology: Lithosphere and upper mantle; 7209 Seismology: Earthquake dynamics and mechanics. Read Full Article (file size: 145234 bytes) Cited by Citation: Gök, R., et al. (2003), Shear wave splitting and mantle flow beneath LA RISTRA, Geophys. Res. Lett., 30(12), 1614, doi:10.1029/2002GL016616. Copyright 2003 by the American Geophysical Union.

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