HR: 0800h
AN: S41B-0558    [Abstracts]
TI: Complex Upper Mantle Seismic Structure Across the Southern Colorado Plateau / Basin and Range II: Results from Receiver Function Analysis
AU: * Gilbert, H
EM: hersh@purdue.edu
AF: Purdue Universirty, Department of Earth and Atm. Sci. 550 Stadium Mall Drive, West Lafayette, IN 47907, United States
AU: Fouch, M J
EM: fouch@asu.edu
AF: Arizona State University, School of Earth and Space Exploration PO Box 871404, Tempe, AZ 85287, United States
AB: Connections between surface tectonics and mantle dynamics have long been investigated. The current configuration of the Transportable Array (TA) component of USArray provides nearly uniform sampling of the upper mantle that underlies much of the tectonically active western United States. The ~70 km spacing of TA stations densely sample the upper mantle discontinuities at the nominal depths of 410 and 660 km with seismicity broadly distributed over a range of azimuths and distances providing excellent coverage. The upper mantle discontinuities are thought to mark phase transition of minerals within the mantle to denser configurations. Changes in the depths of the discontinuities can thus be used to infer thermal variations at specific depths in the mantle based on the pressure-temperature relation of the responsible phase transitions. Here we use receiver functions calculated by teleseismic events recorded by the TA to investigate the depths of the discontinuities in the southwestern United States focusing on the transition between the Basin and Range and the Colorado Plateau. Previous studies of the depths of these discontinuities in the western United States have found each interface to exhibit ~30 km of topography. Observations presented here indicate a similar amount of discontinuity topography with depths of the 660-km discontinuity varying from less than 640 km in the central Colorado Plateau to greater than 670 km in the southern Basin and Range. The 410-km discontinuity shallows to less than 405 km depth in the southern Basin and Range and reaches near 420 km depth in the Colorado Plateau. Exploring azimuth fluctuations in receiver functions sampling discontinuity structures from different directions indicates a greater amount of variability in the depth of the 660-km discontinuity when sampled from eastern versus western azimuths in the southern Basin and Range than in the Colorado Plateau. Attributing variations in discontinuity depths to anisotropy suggests a more complex pattern of anisotropy beneath the southern Basin and Range than the Colorado Plateau and that a significant component of that anisotropy may be focused towards the base of the upper mantle.
DE: 7205 Continental crust (1219)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8164 Stresses: crust and lithosphere
SC: Seismology [S]
MN: 2007 Fall Meeting