Long offset walkaway and circle VSP in Nankai trough seismogenic zone

The purpose of this VSP surveys is to illuminate deep plate boundary and mega-splay faults with high resolution imaging, and to build Vp and Vs model in this area. The seismic data were successfully acquired with the 53.4km walkaway VSP and the circular VSP with 3.5km radius with 16 three-component wireline borehole seismic tools in the cased hole. Zero offset VSP were carried out as well. The long offset survey like this long distance and deep target was first-ever carried out in academia and industrial field. Preliminary P-P reflection image shows high resolution reflections from splay faults. Anisotropy results using direct arrival time from circle VSP indicate anisotropy and its orientation is consistent with the orientation of Philippine plate subduction and the stress orientation from bore hole image. We are planning 3D spiral VSP in 2013.