HR: 08:55h
AN: S51D-04    [Abstracts]
TI: Inversion of depth-dependent small-scale heterogeneity spectra in the Earth using transmission fluctuations of logarithmic amplitude and phase data
AU: * Zheng, Y
EM: yzheng@pmc.ucsc.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, United States
AU: Wu, R
EM: wrs@pmc.ucsc.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, United States
AB: The transmission fluctuations of log-amplitude and phase data across a seismic array provide sensitive probe for the heterogeneities at depth. The coherence functions formed using these transmission fluctuations can be used to invert for the depth-dependent small-scale heterogeneity spectrum in the context of variable background velocity model whereas the previous theory was formulated with a constant background velocity. Our newly extended theory allows us to apply the method to data collected on the Earth's surface. We investigated the depth sensitivity of the logA and phase coherence functions. The angular coherence function (ACF) and the transverse coherence function (TCF) are two extreme cases of the joint transverse and angular coherence function (JTACF). The phase ACF has sensitivity at shallow depths; the phase TCF has almost uniform sensitivity over all depths; the phase JTACF has focused sensitivity around depth where the paths of the two events intersect. Likewise, the logA TCF and ACF have very poor depth resolution. The depth sensitivity of logA JTACF is similar to that of the phase JTACF. The spectral inversion is formulated as a generalized inversion problem. A lithosphere-asthenosphere model is tested for numerical validation using the finite difference generated seismograms. It shows that using JTACFs with angular separation up to 15°, we were able to recover the heterogeneity spectra of the two-layer model. Our method recovers the heterogeneity spectrum at the high wavenumber end and it is supplementary to the traditional seismic tomography where only the low wavenumber end information is retrieved. We will also show some preliminary results of the heterogeneity spectrum under Japan using the HiNet data.
DE: 7203 Body waves
DE: 7218 Lithosphere (1236)
DE: 7260 Theory
DE: 7270 Tomography (6982, 8180)
DE: 8110 Continental tectonics: general (0905)
SC: Seismology [S]
MN: 2007 Fall Meeting