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Experimental Airgun Survey Using DONET Seafloor Observatories to Estimate Seismic Anisotropy in the Nankai Trough, Japan
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 77th EAGE Conference and Exhibition 2015, Jun 2015, Volume 2015, p.1 - 5
Abstract
The Nankai Trough, Japan is a major subduction zone, and huge mega-thrust earthquake repeatedly occurred. In this area, DONET (Dense Oceanfloor Network systems for Earthquake and Tsunamis) seafloor cabled seismic network, and IODP C0002G borehole observatory were distributed. In KR13–17 cruise, conducted by R/V Kairei in November 2013, we performed an experimental survey using DONET and IODP C0002G seismometers and airgun shooting to estimate seismic anisotropy in the Nankai Trough. Seismic anisotropy can be a proxy of stress state, which would be a key parameter governing its fault dynamics triggering mega-thrust earthquake in the subduction zone. In KR13–17 cruise, we performed airgun circle shooting around DONET and IODP C0002G seismometers. Then we computed radial and transverse components for each shot-receiver azimuth from original horizontal records of seismometers. In radial and transverse components, P-S converted waves reflected from the bottom of shallow sediment layers were clearly visible. We then obtained azimuthal seismic anisotropy below seismometers in shallow sediment. Obtained results have good agreement with results from another method and dataset. We plan to conduct next survey in the same survey lines to detect temporal evolution of the seismic anisotropy in the seismogenic subduction zone.