HR: 1340h
AN: T33A-1351    [Abstracts]
TI: Southern California Plate Parallel Azimuthal Anisotropy from Surface Wave data
AU: * Prindle-Sheldrake, K L
EM: kenton_prindle@umail.ucsb.edu
AF: University of California, Santa Barbara, UC Santa Barbara-Building 526 , Santa Barbara, CA 93106-9630 United States
AU: * Prindle-Sheldrake, K L
EM: kenton_prindle@umail.ucsb.edu
AF: Institute for Crustal Studies, 1140 Girvetz Hall UC Santa Barbara, Santa Barbara, CA 93106-1100 United States
AU: Tanimoto, T
EM: toshiro@geol.ucsb.edu
AF: University of California, Santa Barbara, UC Santa Barbara-Building 526 , Santa Barbara, CA 93106-9630 United States
AU: Tanimoto, T
EM: toshiro@geol.ucsb.edu
AF: Institute for Crustal Studies, 1140 Girvetz Hall UC Santa Barbara, Santa Barbara, CA 93106-1100 United States
AB: Azimuthal anisotropy was recovered in Southern California using data from CISN (California Integrated Seismic Network) broadband seismic network. Approximately 150 stations were utilized in this study with the number of paths reaching about 3000. Phase velocity maps including azimuthal anisotropy terms were generated for Rayleigh waves at frequencies 0.02 Hz through 0.055 Hz. The inversion for phase velocity maps included lateral heterogeneity and 2 theta terms for anisotropy. First, we have carefully tested the resolving power of our data by computing resolution kernels and by performing checker-board input tests for anisotropy. Resolution analyses indicate that the data are capable of resolving 2 theta anisotropy terms for approximately the size 150 km x 150 km. It is not possible to determine short wavelength scale anisotropy below the length scale 100 km. Derived anisotropy patterns seem to display interesting tectonic implications. Rayleigh wave azimuthal anisotropy results show orientations of the fast axis parallel to the motion of the Pacific plate on the west side of the San Andreas fault for frequencies between 0.02 Hz and 0.055 Hz. East of the San Andreas fault, Rayleigh wave azimuthal anisotropy is comparatively small from 0.02 Hz to 0.03 Hz, suggesting a substantial anisotropic contrast across the tectonic margin in the upper mantle. The Pacific plate parallel anisotropy orientations west of the San Andreas may indicate upper mantle flow under the Pacific plate. At low frequencies, between 0.02 Hz and 0.03 Hz, the Salton Trough region has fast axis oriented perpendicular to Pacific plate motion and overall strike of margin faults, such as the San Andreas. Above 0.03 Hz the orientation changes to parallel to Pacific plate motion. If spreading underneath the Salton Sea exists, this pattern may indicate orientation of anisotropy related to the spreading flow in the upper mantle. At higher frequencies, the amplitude of anisotropy increases on both sides of this plate boundary region, indicating strong crustal anisotropy.
DE: 7230 Seismicity and seismotectonics
DE: 7255 Surface waves and free oscillations
DE: 7260 Theory and modeling
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting