Japan Agency for Marine-Earth Science and Technology, Japan

Integrated Ocean Drilling Program (IODP) Expedition 316 is part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) complex drilling project (CDP). This coordinated, multiplatform, and multiexpedition 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 primary goals for Expedition 316 are to drill and core two proposed sites, NT1-03B and NT2-01B. Site NT1-03B will be drilled and cored to a total depth (TD) of 950 meters below seafloor (mbsf), and Site NT2-01B will be drilled and cored to a total depth of 1000 mbsf. Hole C at Site NT2-01B will also be fitted with a reentry cone and cased to TD in preparation for cross-hole hydrologic experiments and installation of monitoring equipment planned for future operations. Expedition 316 is intended to comprehensively evaluate the deformation, inferred depth of detachment, structural partitioning, and fault zone physical characteristics at the frontal thrust (proposed Site NT1-03B) and at the shallow portion of the megasplay system (proposed Site NT2-01B). Critical data to be collected include physical properties of the fault zone and surrounding wall rocks, diagenetic, chemical, and other evidence for fluid flow, and age determination of material above and below both fault systems in order to begin to estimate transport histories and fluid flow response in different areas of the forearc. These data will be collected through complete coring and laboratory measurement and downhole measurements (in situ temperature measurements and wireline logging) whose exact composition will depend on the results of logging-while-drilling (LWD) operations during Expedition 314 (LWD Transect). These operations and data will constrain accumulation and release of strain and the relationships between pore pressure, fault slip, strain, and fluid flow in the near field of the shallow megasplay and the frontal thrust. Taken together, these operations will constrain the long-term slip behavior of the megasplay and frontal thrust fault systems, and document rock properties and in situ conditions within a deep forearc basin and the interior of an accretionary prism. In this Scientific Prospectus we present the scientific background and objectives, drilling operations designed to achieve them, contingency strategies, and coordinated NanTroSEIZE Stage 1 research planning for sharing Stage 1 samples and data.