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. The fundamental scientific objectives of the NanTroSEIZE 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.

Drilling during Integrated Ocean Drilling Program (IODP) Expedition 348 will comprise riser drilling with the primary objective of deepening existing Hole C0002F to 3600 meters below seafloor (mbsf). These operations will extend drilling conducted during IODP Expeditions 326 and 338. The entire expedition will cover a period of 130 days, beginning on 13 September 2013 and ending on 20 January 2014.

Site C0002 is located in the Kumano forearc basin above the seismogenic, and presumably locked, portion of the plate boundary thrust system. The Kumano Basin sedimentary sequence and uppermost part of the accretionary prism were drilled, logged, and sampled during IODP Expeditions 314 (logging while drilling [LWD] to 1401.5 mbsf), 315 (coring to 1057 mbsf), and 338 (LWD to 2005 mbsf and coring to 1120 mbsf). During Expedition 348, drilling to 3600 mbsf or deeper will access the deep interior of the Miocene inner accretionary prism and will allow characterization of a unique tectonic environment that has never before been sampled in situ by ocean drilling. The primary goals include LWD, casing to a target depth of 3600 (or 4400) mbsf, and analyses of cuttings, mud gases, and limited cores to address the four primary scientific objectives: (1) determine the composition, stratigraphy, and deformational history of the Miocene accretionary prism; (2) reconstruct its thermal, diagenetic, and metamorphic history; (3) determine horizontal stress orientations and magnitudes; and (4) investigate the mechanical and hydrological properties of the upper plate of the seismogenic plate boundary. After Expedition 348, current plans call for the hole to be deepened to cross and sample the megasplay fault at ~5200 mbsf during a later expedition in 2015.

This Scientific Prospectus outlines the scientific rationale, objectives, and operational plans for drilling during Expedition 348 and describes the main contingency options.