HR: 0830h
AN: S31E-0806    [PDF]
TI: Joint tomographic inversion of body and surface waves for upper mantle structure
AU: * West, M E
EM: west@nmsu.edu
AF: Dept. of Physics, New Mexico State University, Las Cruces, NM 88003
AU: Gao, W
EM: gao@speer.geo.utexas.edu
AF: Jackson School of Geological Sciences, University of Texas at Austin 1 University Station C1100, Austin, TX 78712
AU: Grand, S P
EM: steveg@speer.geo.utexas.edu
AF: Jackson School of Geological Sciences, University of Texas at Austin 1 University Station C1100, Austin, TX 78712
AB: We present a tomographic method which combines teleseismic shear wave delay times and Rayleigh wave phase velocities into a single joint inversion for shear wave velocity structure. Teleseismic body wave tomography, based on PASSCAL-type broadband deployments provides, arguably, the highest lateral resolution of features in the upper mantle. However, the need to account for structures outside the resolved area limits the resulting image to a lateral comparison of relative velocity, while steeply-dipping raypaths diminish the vertical resolution at shallow depths. Conversely, surface wave inversions have their greatest vertical resolution at shallow depths, and they provide measurement of absolute seismic velocities. The long wavelengths required to probe the mantle however, lack the lateral resolution afforded by body waves. Several recent papers have used a 1D velocity model, derived from surface waves, as a baseline to which the body wave-derived variations are applied. The deployment of larger aperture seismic arrays and USArray allow the integration of spatially-varying surface wave observations. We present a straightforward method in which surface wave velocities are converted into traveltimes and sensitivity kernels that can be directly incorporated into existing body wave tomography schemes. The strengths of this method are twofold. First, it is blind to the specific methods used to derive surface wave velocities and body wave delay times. These could be accomplished by different researchers using different events, and even different seismic arrays. Second, the approach can be applied rapidly to most body wave delay time inversion schemes with minimal modification. We demonstrate the method on data from the PASSCAL-supported LA RISTRA array in the southwest U.S. The temporary 950-km linear array provides a large set of body wave traveltimes and surface wave velocities over periods of 10-150 s. Independent crustal thickness constraints, in this case provided by receiver function analysis, can be incorporated as well. We use this data and synthetics to demonstrate the benefits of the joint inversion method as well as special considerations required to weight the two complimentary datasets.
DE: 3260 Inverse theory
DE: 7203 Body wave propagation
DE: 7218 Lithosphere and upper mantle
DE: 7255 Surface waves and free oscillations
DE: 8109 Continental tectonics--extensional (0905)
SC: Seismology [S]
MN: 2003 Fall Meeting