Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-SS Seismology

[S-SS26] Seismic wave propagation: Theory and Application

Tue. May 26, 2015 2:15 PM - 4:00 PM 103 (1F)

Convener:*Tatsuhiko Saito(National Research Institute for Earth Science and Disaster Prevention), Hisashi Nakahara(Solid Earth Physics Laboratory, Department of Geophysics, Graduate School of Science, Tohoku University), Jun Matsushima(School of Engineering, The University of Tokyo), Kiwamu Nishida(Earthquake Research Institute, University of Tokyo), Kazuya Shiraishi(JGI, Inc.), Chair:Azusa Shito(京都大学), Shunsuke Takemura(Yokohama City University)

3:00 PM - 3:15 PM

[SSS26-15] Comparison between ray theory and synthetic seismograms for transversely isotropic media

*Anselme BORGEAUD1, Kensuke KONISHI1, Robert J. GELLER1, Kenji KAWAI2 (1.Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 2.Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, University of Tokyo)

Keywords:DSM, Travel time, D double prime, Upper mantle, Anisotropy, S-wave splitting

Imaging seismic anisotropy is essential for a better understanding of geodynamics, since it provides information on deformation and flow in the crust and mantle. S-wave splitting has been widely used to infer the presence and extent of anisotropy. The inference of anisotropy from S wave splitting relies, however, on ray theory, which is strictly valid only for infinitely high frequencies, and thus may not accurately reflect real finite-frequency seismic data. For example, a recent study by Komatitsch et al. (2010) showed that splitting of diffracted S waves in the D'' region, just above the CMB, is present in synthetics computed for an isotropic velocity model. In this study we compute travel times for a transversely isotropic (TI) medium using a newly developed software package (Konishi et al., JpGU, 2015). We then compute full-wave synthetics using the Direct Solution Method (DSM; Kawai et al., 2006). We focus on two regions of the mantle: D'' and the upper mantle. We confirm apparent S-wave splitting in synthetics computed for the isotropic IASP91 velocity model for epicentral distances over 100 degrees, in agreement with the results of Komatitsch et al. (2010). We also compare the predictions of geometrical optics to synthetics for TI models for phases which sample the upper mantle and the D'' region.