Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG64] Ocean Floor Geoscience

Thu. May 28, 2015 2:15 PM - 4:00 PM A05 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Kyoko Okino(Ocean Research Institute, University of Tokyo), Keiichi Tadokoro(Research Center for Seismology, Volcanology and Earthquake and Volcano Research Center, Nagoya University), Osamu Ishizuka(Geological Survey of Japan, AIST), Tomohiro Toki(Faculty of Science, University of the Ryukyus), Narumi Takahashi(Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology), Chair:Mikiya Yamashita(Japan Agency for Marine-Earth Science and Technology), Tomohiro Toki(Faculty of Science, University of the Ryukyus)

2:30 PM - 2:45 PM

[SCG64-31] Deformation structure obtained by high resolution multi-channel seismic reflection survey around Nankai Trough axis

*Mikiya YAMASHITA1, Ayako NAKANISHI1, Yasuyuki NAKAMURA1, Hikaru IWAMARU1, Seiichi MIURA1, Shuichi KODAIRA1, Yoshiyuki KANEDA1 (1.JAMSTEC)

Keywords:MCS survey, Nankai Trough, proto thrust

The big disaster earthquakes had often occurred in the Nankai Trough with a great Tsunami event. In order to reduce a great deal of damage to coastal area from both strong ground motion and tsunami generation, it is necessary to understand rupture synchronization and segmentation of the Nankai megathrust earthquake. We focus on the deformation structure around the Nankai Trough. However, there are few seismic survey lines in the trough axis in the Nankai Trough. Therefore, we planned new survey around the trough axis in the Nankai Trough in order to obtain the high resolution structure.
Japan Agency for Marine-Earth Science and Technology (JAMSTEC) carried out new high resolution multi-channel seismic reflection (MCS) surveys using portable system over 1,500 km of line length from off Kochi to Kii Peninsula during 2013-2014. The seismic source used was an G-gun cluster array of 4 air guns with total volume of 380 cubic inches (5.24 L). The hydrophone cable is ca. 1200 m long, having 192 channels at an interval of 6.25 m. The MCS data were processed through a standard seismic processing flow, which consists of noisy-trace editing, 20?200 Hz band-pass filtering, velocity analysis with every ca.313 m intervals picking, normal moveout, Common Depth Point (CDP) stacking, and poststack time migration.
We obtained 23 MCS profiles around the Nankai Trough. Clear frontal thrusts are imaged in the margin of Nankai Trough axis. We recognized distinct proto thrust zone in the south part of the frontal thrust. This results yield the possibility of extended rupture area in the Nankai Trough.
This study is part of "Research project for compound disaster mitigation on the great earthquakes and tsunamis around the Nankai Trough region" funded by MEXT, Japan.