HR: 0800h
AN: T31A-0269    [Abstracts]
TI: Crustal and Upper Mantle Structure beneath Central South America Deduced from ScS Reverberation Waveforms and Receiver Functions
AU: Okaue, Y
AF: Department of Geophysics, Kyoto University, Sakyo, Kyoto, 606-8502, Japan
AU: * Kuge, K
EM: keiko@kugi.kyoto-u.ac.jp
AF: Department of Geophysics, Kyoto University, Sakyo, Kyoto, 606-8502, Japan
AU: Kato, M
EM: mkato@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto University, Sakyo, Kyoto, 606-8501, Japan
AB: We investigated the crust and upper mantle structure beneath the central South America, approximately at 20 degree south, by modeling ScS reverberation waveforms and receiver functions at GSN stations. ScS reverberation waveforms are sensitive to the path-averaged S-wave velocities, attenuation, and depths and reflection coefficients of discontinuities in the crust and mantle. Our procedure to determine these parameters follows that of Kato et al. (2001) utilizing ray-based theoretical waveform modeling and grid search optimization. Finiteness of source time duration is additionally taken into consideration in synthesizing waveforms of a great earthquake. Depths of mantle discontinuities were separately estimated from arrival times of PS conversion phases on receiver functions. We also modeled receiver functions from early P coda to determine crustal structure. In this study, significant differences were found between the western coast and eastern continent. Beneath BDFB in the eastern continent, the Conrad and Moho were estimated at depths of 22 and 40 km, respectively. Beneath NNA in the western coast, four discontinuities were detected in a range of depth from 25 to 70 km. Observations on the receiver functions imply an inclination of the deep discontinuities, which can be the manifestations of the top of the subducting Nazca plate. A high value of average Q was obtained for the upper mantle beneath NNA, but not beneath BDFB. Since the value is much higher than predicted from the expected mantle transition zone temperature, the high Q region might exist in the uppermost mantle, being attributed to the subducting Nazca plate. In the transition zone, the 410-km discontinuity is shallow beneath the western coast. The mantle transition zone is thinner in the western coast than in the eastern continent. On the receiver functions in the western coast, we were able to identify a phase possibly from the 520-km discontinuity. Using SS reflection coefficients from the ScS reverberations and PS conversion coefficients from the receiver functions, we attempted to obtain the upper bounds of density and Vs contrasts at mantle discontinuities.
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 9360 South America
SC: Tectonophysics [T]
MN: 2007 Fall Meeting