HR: 08:30h
AN: T31D-03    [Abstracts]
TI: Constraints on Deformation Geometry Beneath Japan From Observations and Models of Seismic Anisotropy
AU: * Long, M D
EM: mlong@mit.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139
AU: van der Hilst, R D
EM: hilst@mit.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139
AU: de Hoop, M V
EM: mdehoop@math.purdue.edu
AF: Center for Computational and Applied Mathematics, Purdue University, 150 N. University St., West Lafayette, IN 47907
AU: Hager, B H
EM: bhhager@mit.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139
AB: Observations of seismic anisotropy such as shear wave splitting measurements contribute much to our understanding of deformation in the Earth. In the context of a complicated tectonic environment such as a subduction zone, however, the interpretation of splitting measurements associated with upper mantle anisotropy and deformation is far from straightforward. Because shear wave splitting data sets contain a wealth of information that can illuminate crucial aspects of subduction dynamics, the robust interpretation of splitting measurements in the context of a subduction zone is an important area of research. In this study, we present a suite of two-dimensional numerical flow models that describe upper mantle deformation above and below a kinematically defined subducting plate. From the resulting velocity and finite strain fields, combined with realistic models for lattice preferred orientation (LPO) in olivine, we develop two-dimensional anisotropic models and predict detailed patterns of shear wave splitting. We compare our predicted patterns of shear wave splitting to a database of approximately 2,000 high-quality shear wave splitting measurements from 64 broadband stations of the Japanese F-net seismic network. This unique dataset of SKS, SKKS, and local and teleseismic S splitting over a dense array covers a wide range of incidence angles, incoming polarization angles, and backazimuths, and is therefore well-suited for the detailed consideration of complex anisotropic structures in the upper mantle. Our combined modeling/observational approach allows us to identify geodynamically plausible models that are consistent with a spatially dense splitting dataset. Here we present anisotropic models that are consistent with the features of the shear wave splitting dataset, evaluate the adequecy of two-dimensional approximations to a three-dimensional subduction zone, and consider complications in anisotropic structure such as the presence of B-type olivine fabric.
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005