TY - GEN
T1 - Vp/Vs and shear-wave splitting at the seismogenic plate subduction zone
T2 - Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
AU - Tsuji, Takeshi
AU - Nakata, Norimitsu
AU - Matsuoka, Toshifumi
AU - Dvorkin, Jack
AU - Nakanishi, Ayako
AU - Kodaira, Shuichi
N1 - Funding Information:
Nishizawa, O. (AIST) gave us helpful comments. This research was supported by the programs of the Grant-in-Aid for Young Scientists (B) from the Japan Society for the Promotion of Science (20760568).
PY - 2010
Y1 - 2010
N2 - 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.
AB - 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.
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U2 - 10.1190/1.3513155
DO - 10.1190/1.3513155
M3 - Conference contribution
AN - SCOPUS:85055496647
SN - 9781617389801
T3 - Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
SP - 1635
EP - 1640
BT - Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010
PB - Society of Exploration Geophysicists
Y2 - 17 October 2010 through 22 October 2010
ER -