HR: 1340h
AN: T23A-0527    [Abstracts]
TI: Statistical properties of seismic anisotropy in the upper mantle based on geodynamic models
AU: * Becker, T W
EM: twb@usc.edu
AF: University of Southern California, Department of Earth Sciences, Los Angeles, CA 90089-0740 United States
AU: Chevrot, S
EM: Sebastien.Chevrot@cnes.fr
AF: Observatoire Midi Pyrenees, Laboratoire de Dynamique Terrestre et Planetaire, Toulouse, 31400 France
AU: Schulte-Pelkum, V
EM: vera_sp@cires.colorado.edu
AF: CIRES, University of Colorado, Benson Earth Sciences Building Department of Geological Sciences, Campus Box 399 2200 Colorado Ave., Boulder, CO 80309-0399 United States
AU: Blackman, D
EM: dblackman@ucsd.edu
AF: IGPP, SIO, UC San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0225 United States
AB: We evaluate global models of synthetic seismic anisotropy for the upper mantle and their implications for imaging flow and compositional structure by means of seismologic inversions. Our flow models are based on mantle circulation computations using both semi-analytical, spectral methods and a spherical finite element method for cases with more realistic rock rheologies. From the flow models, lattice preferred orientation (LPO) is computed using the kinematic mineral physics theory of Kaminski & Ribe. The LPO can be converted to elasticity tensors, which we then analyze as a function of depth and tectonic location. Among the results of this project are maps of tensor symmetry components strengths; those are useful to estimate the complexity of a given region in terms of anisotropy, and so to evaluate the appropriateness of various simplifications typically employed in seismologic and geodynamic models. Particularly, we can see how much of the total anisotropy is captured by hexagonal symmetry, and what backazimuth dependence may be seen in shear wave splitting. Such synthetic anisotropy maps are also a useful backdrop against which to judge the length-scales and depth of origin of anisotropic heterogeneity in oceanic and continental lithosphere and mantle. This is one of the major outstanding questions in this field, with general implications for the mechanical behavior and structure of the asthenosphere. We furthermore evaluate the correlation between hexagonal anisotropy parameters for S and P wave anisotropy and compare those with natural samples. Such scaling relationships for anisotropy parameters may be employed to reduce the number of free parameters of seismic imaging inversions based on a priori information. On large scales, the best-fit transverse isotropy axes align well with the largest finite strain ellipsoid axes, confirming our earlier conclusions about the ability of flow models to explain azimuthal anisotropy from surface waves.
DE: 3625 Petrography, microstructures, and textures
DE: 5199 General or miscellaneous
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005