Cardiff University, United Kingdom

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) program is a coordinated, multiexpedition drilling project 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. Some of the fundamental scientific objectives of the NanTroSEIZE drilling project include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout the active plate boundary system to a depth of 7000 m below seafloor. It is also important to show how such properties evolve from shallow, presubduction conditions in the Shikoku Basin to greater depths of the accretionary prism where fault slip is seismogenic. Within this context, the primary goals for Integrated Ocean Drilling Program (IODP) Expedition 333 were: (1) drilling and coring of previously unsampled intervals of sediment and basalt at IODP Sites C0011 and C0012 in the Shikoku Basin, together with downhole measurements of temperature, and (2) drilling and coring at a site near the updip terminus of the megasplay fault, as proposed in Ancillary Project Letter (738-APL: Nankai Trough Submarine Landslide History [NanTroSLIDE]). The most important accomplishments were (1) determination of heat flow at Sites C0011 and C0012, (2) coring through a transition in physical properties within the upper part of the Shikoku hemipelagite, (3) repeated coring and sampling of fluid above the sediment/basement interface for shore-based geochemical studies, (4) coring into the basalt to 100 m below the sediment/basalt interface, and (5) drilling and sampling a nearly complete slope basin stratigraphic succession comprising six mass transport deposits that record approximately 1 m.y. submarine landsliding history near the shallow megasplay fault zone area.