Japan Agency for Marine-Earth Science and Technology, Japan

The Nankai Trough along Japan coast, which has the longest historical record of subduction zone earthquakes, is the target of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) complex drilling project in the framework of Integrated Ocean Drilling Program (IODP). This coordinated, multiplatform, and multi-expedition drilling project is designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. The first stage of NanTroSEIZE which consists of three expeditions (Expedition 314, 315 and 316) was carried out from September 2007 to February 2008. Expedition 316 was designed to evaluate the deformation, the inferred depth of detachment, the structural partitioning, the fault zone physical characteristics and fluid flow at the frontal thrust and at the shallow portion of the megasplay system. We drilled two sites in the megasplay region (fault zone at Site C0004, and slope sediments at Site C0008) and two Sites C0006 and C0007 in the frontal thrust region. Fault rocks in both region and rocks/sediments from hanging walls and foot walls were successfully recovered. We measured anisotropy of magnetic susceptibility for samples from Expedition 316 cores. Magnetic susceptibility showed variety corresponding to lithology at each drilling sites. Although the anisotropy degree (P') is generally low, the shape parameter (T) showed difference in the fault zone at Site C0004. While the slope sediments at Site C0008 show positive T values which corresponds to uni-axial shortening, samples within fault zone at Site C0004 showed scattered T values. This possibly suggests effect of mechanical deformation.