HR: 1340h
AN: T33A-1338    [Abstracts]
TI: Seismic anisotropy in the Western US as a testbed for advancing combined models of upper mantle geodynamics and texturing
AU: * Becker, T W
EM: twb@usc.edu
AF: Department of Earth Sciences, University of Southern California, Zumberge Hall of Science 3651 Trousdale Pkwy, Los Angeles, CA 90089-0740 United States
AU: Blackman, D K
EM: dblackman@ucsd.edu
AF: Institute for Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego 9500 Gilman Drive, La Jolla, CA 92093-0225 United States
AU: Schulte-Pelkum, V
EM: vera_sp@cires.colorado.edu
AF: CIRES, University of Colorado Boulder, Department of Geological Sciences 399, Boulder, CO 80309-0399 United States
AB: Observed seismic fast axes are popularly equated with directions of mantle flow. In order to substantiate this assumption, we present improved models of mantle flow, derived textural anisotropy, and predicted seismic anisotropy. Results include global models, where we compare surface wave based seismologic inversions with predictions from large-scale mantle circulation computations. For body wave anisotropy, we focus on a regional model of the western United States, a relatively simply-parameterized region where a wide range of seismic data is available. Our work addresses the three stages needed to connect mantle flow and anisotropy: flow, texture development, and wave propagation in a heterogeneous upper mantle and lithosphere. For the flow models, we explore lateral variations in viscosity, improved rheologic realism, and joint regional/global convection computations. In terms of mineral physics, we compare predictions from finite strain (FS), lower-bound (LB), and kinematic (KR) texture formation theories. The seismological modeling includes computing apparent splitting from spatially variable, not necessarily hexagonal anisotropic elastic tensors. We also evaluate the potential role of the crust in partly obfuscating the underlying dynamic processes. Preliminary results indicate that FS, LB, and KR models are similar except in regions of large spatial variations in flow, as expected. Mantle circulation models that take the inferred Farallon slab density anomalies at depth into account show a return flow roughly opposite to the surface motion of North America. Those models tend to fit the data better, indicating a possible avenue to better constrain tectonic processes in the study region over time.
DE: 9350 North America
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8150 Plate boundary--general (3040)
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting