Vp/Vs and shear-wave splitting at the seismogenic plate subduction zone: Insight into effective-stress and pore pressure distribution

Takeshi Tsuji, Norimitsu Nakata, Toshifumi Matsuoka, Jack Dvorkin, Ayako Nakanishi, Shuichi Kodaira

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

To predict the stress state as well as pore pressure in the Nankai accretionary prism southwest Japan, we estimated the ratio of P-wave velocity over S-wave velocity (Vp/Vs) and shear-wave splitting using multi-component ocean bottom seismometers (OBS) data. Because it is difficult to identify PS-converted reflection waveforms for each of the geological boundaries in the deep offshore region, we focused on the more easily identified PPS-refracted waveforms. We estimated the average Vp/Vs within the sedimentary section by using the time lag between P-refracted waves and PPS-converted waves. The estimated Vp/Vs changed abruptly at the trough axis, mainly because of compaction associated with the accretion process. Vp/Vs gradually increased landward from the trough axis to the mega-splay fault. The increase in Vp/Vs might indicate abnormal pore pressure below the mega-splay fault. To estimate the stress-induced fracture orientation, we computed the fast polarization direction and principal amplitude direction from PPS-converted waves. The anisotropic characteristics change at the mega-splay fault: the fast polarization direction and principal amplitude direction are parallel to the trough (transverse) landward of the mega-splay fault. Furthermore, we observe predominant velocity anisotropy around the mega-splay fault. These observations suggest that both the preferred fracture orientation and the principal stress orientation are oblique to the direction of subduction near the mega-splay fault.

Original languageEnglish
Title of host publicationSociety of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
PublisherSociety of Exploration Geophysicists
Pages1635-1640
Number of pages6
ISBN (Print)9781617389801
Publication statusPublished - Jan 1 2010
EventSociety of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010 - Denver, United States
Duration: Oct 17 2010Oct 22 2010

Publication series

NameSociety of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010

Other

OtherSociety of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
CountryUnited States
CityDenver
Period10/17/1010/22/10

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All Science Journal Classification (ASJC) codes

  • Geophysics

Cite this

Tsuji, T., Nakata, N., Matsuoka, T., Dvorkin, J., Nakanishi, A., & Kodaira, S. (2010). Vp/Vs and shear-wave splitting at the seismogenic plate subduction zone: Insight into effective-stress and pore pressure distribution. In Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010 (pp. 1635-1640). (Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010). Society of Exploration Geophysicists.