HR: 0800h
AN: T21B-0585    [Abstracts]
TI: Models of Seismic Anisotropy and Upper Mantle Deformation at the San Andreas Fault System: Investigation of the Role of Crust-Mantle Coupling
AU: Roy, M
EM: mroy@unm.edu
AF: Dept of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, United States
AU: * Tetreault, J L
EM: joya@unm.edu
AF: Dept of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, United States
AU: Gaherty, J
EM: gaherty@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, United States
AU: Chen, P
EM: pochen@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, United States
AU: Zhao, L
EM: zhaol@usc.edu
AF: Institute of Earth Sciences, Academia Sinica, Taipei, 115, Taiwan
AB: Upper mantle seismic anisotropy patterns at the San Andreas fault system are uniquely suited to investigating the role of crust-mantle coupling within the lithosphere. Published interpretations of seismic anisotropy in northern California include a two-layer model with fault-parallel anisotropy in the upper layer and nearly fault- perpendicular, E-W anisotropy in the lower layer. This has been interpreted to suggest that plate motions play a role in generating seismic anisotropy in the upper mantle in this region. In contrast, in southern California, the dominance of E-W anisotropy has been interpreted as a primarily asthenospheric signal, with little influence of the lithosphere. In this project, an integrated seismic-geodynamic analysis is being developed and applied to better quantify the role of lithospheric (plate) motions on the seismic anisotropy patterns at the San Andreas fault system with the goal of understanding the rheologic scenarios that allow these patterns to arise. We model mantle flow for the Pacific-North America plate boundary as a viscous channel using the well-studied surface kinematic field and inferred deeper asthenospheric flow patterns as boundary conditions. The fluid within the channel is characterized by depth-stratified rheologic properties, representing upper mantle within the mantle lithosphere and in the asthenosphere beneath. We investigate how mantle flow would produce olivine lattice preferred orientation (LPO) fabrics with a 3-D Cartesian implementation of a published kinematic code to calculate LPO by dynamic recrystallization. Our geodynamic models focus on how rheologic parameters govern the fabric development and whether we can interpret the observed patterns of seismic anisotropy at the San Andreas fault system in terms of the relationship between the observed plate motions at the surface and flow in the asthenosphere. These models will serve as priors in a tomographic inversion of new observations of seismic anisotropy derived from the USArray Transportable Array.
DE: 7218 Lithosphere (1236)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8162 Rheology: mantle (8033)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting