2D/3D seismic imaging of Kumano-nada in the central Nankai Trough - as a mission for the IODP Implementing Organization -

Yukari Kido,Shin’Ichi Kuramoto,Asahiko Taira,Yoshinori Sanada,Tadashi Okano,Gregory F Moore,Hajime Saga,Shigenobu Uraki,Jin-Oh Park,Kyaw Thu Moe

doi:10.1190/segj092009-001.44

Yukari Kido, Shin’Ichi Kuramoto + Show 8 more

https://doi.org/10.1190/segj092009-001.44

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Publication Date: Jan 1, 2009

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In the Nankai Trough off Kii Peninsula, the first scientific drilling by D/V Chikyu commenced in September 2007 as a major component of the Integrated Ocean Drilling Program (IODP). One of its scientific challenges is to drill to the seismogenic zone to reveal the nature and mechanism of large earthquake generation. Prior to drilling, we carried out 2D/3D seismic surveys to make decisions of drilling targets by identifying hazards for safe and smooth drilling operation and obtaining detailed characteristics of the accretionary prism. We designed a dense 2D seismic survey to cover the region around the possible drilling sites and 10 km deep penetration. After analysis of the 2D lines showed the best location for the drill sites, we carried out a 3D seismic survey by M/V Nordic Explorer (PGS Geophysical) during April - May 2006 in Kumano-nada off Kii Peninsula in the central Nankai Trough. This was the first 3D site survey operation using a commercial seismic vessel. These dense 2D and 3D seismic surveys provide high resolution images. The surveys fully cover the area of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) drilling targets. Data processing, including Pre-Stack Time Migration (PSTM), was carried out by CGGVeritas, and we conducted Pre-Stack Depth Migration (PSDM) processing with a well tuned velocity model. The information provides fine operation parameters to carry out the NanTroSEIZE drilling program. Utilizing the logging data obtained in the drilling program, we were able to calibrate the depth/velocity model with well markers and to make clear judgments on an exact and true depth of fracture and fault zones in the accretionary prism. The NanTroSEIZE program will continue to drill through 7 km deep penetration down to and through the plate boundary. We will integrate the logging data obtained in NanTroSEIZE drilling with the 3D seismic data and attempt to develop more accurate and detailed information of the deeper region.

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