Japan Geoscience Union Meeting 2014

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Oral

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

[S-SS27_29AM1] Seismic wave propagation: Theory and Application

Tue. Apr 29, 2014 9:00 AM - 10:45 AM 411 (4F)

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:Yohei Yukutake(Hot Springs Research Institute of Kanagawa Prefecture), Kazuya Shiraishi(JGI, Inc.)

10:30 AM - 10:45 AM

[SSS27-P02_PG] Frequency domain calculation of the seismic wavefield propagating along an ocean trench, with a constant Q attenuation

3-min talk in an oral session

*Yuta MITSUHASHI1, Mitsuko FURUMURA2, Ritsuko S. MATSU'URA2, Masahiro SHOJI1 (1.KKE, 2.ADEP)

For shallow interplate earthquakes, large long-period later phases are frequently observed at long distance. Simulations using the finite difference, which we have performed, revealed an important effect of seawater on those later phases (e.g. Furumura et al., 2011).However, attenuation exp(-πft/Q) in the finite difference calculation is set to exp(-πft/(Qof/fo)), meaning Q/f=Qo/fo is set as a constant, where fo is a target frequency of the calculation purpose, and Qo is its corresponding attenuation factor, so it causes some problems especially for waves propagating for a long distance.Then we calculated waves propagating in a 2.5D structure in the frequency domain with FEM to realize Q as a constant instead of Q/f, for both cases with and without seawater. We could confirm the important effect of seawater on later phases as well as the finite difference calculations. Calculated later phases have relative large amplitude for frequencies lower than fo in the Q-constant model compared with the Q/f-constant model. It indicates necessity of estimation of difference between realistic Q and modeled one, when we use the finite difference method. In addition, the results reveal large later phases in the case with seawater, which are rarely seen in the calculated waveforms without seawater. It implies overestimation of magnitude of ocean earthquakes obtained from analysis of waves propagating through a long distance along and across an ocean trench, such as the 1911 off Kikai Island earthquake and the 1933 off Sanriku earthquake observed in Honshu.