HR: 1340h
AN: S23B-1384    [Abstracts]
TI: Finite-Frequency Tomography Using Ambient Seismic Noise in the Presence of Surface Topography
AU: * Zhang, W
EM: wzhang@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, South Ferry Rd., Narragansett, RI 02882,
AU: Shen, Y
EM: yshen@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, South Ferry Rd., Narragansett, RI 02882,
AB: The use of ambient seismic noise to determine the crustal and upper mantle structure has become an established practice in seismology. Compared to the traditional methods that utilize surface waves from earthquakes, it has several advantages, particularly in extending usable waves to short periods and providing detailed constraints at shallow depths. In this study, we calculate the 3D sensitivity kernels for the Green's function derived from the cross-correlation of ambient noise at pairs of stations. Furthermore we assess the effects of surface topography on the sensitivity kernels and their importance in the use of short-period waves. We have developed an implementation of a force source on the surface in a finite-difference method, which has been validated through both the reciprocity theory and a comparison with results from a semi-analytical method. The phase-delay sensitivity kernels for the impulse response between the two vertical components of a pair of station to S-velocity perturbations, for example, are similar to those of Rayleigh waves from earthquakes, as expected. We note that the kernels reach a local minimum value at about one eighteenth wavelength depth below the free surface and have larger values on the free surface. This near surface effect should be taken into account in the seismic wave simulation and we solve this problem by using a non-uniform-grid finite-difference method. To assess the effects of surface topography, we use a boundary-conforming grid in a non-staggered finite-difference method. Surface topography has a strong effect on the distribution of the phase and amplitude sensitivity kernels, particularly for short-period waves. Thus in places with large surface topography, the topographic effects must be taken into account in the use of short-period ambient noise. We will apply these kernels to real data and discuss the resolution and implication of the new method for the crustal and upper mantle structure.
DE: 7200 SEISMOLOGY
DE: 7255 Surface waves and free oscillations
DE: 7270 Tomography (6982, 8180)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting