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doi:10.2204/iodp.sp.322.2009

Abstract

Integrated Ocean Drilling Program (IODP) Expedition 322 is part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). This multiexpedition drilling project was designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with laboratory studies and numerical modeling. The primary goal for Expedition 322 is to characterize the composition, architecture, and state of sediments and upper igneous crust entering the subduction system offshore the Kii Peninsula, Japan. Proposed drilling Site NT1-07A will penetrate ~1200 meters below seafloor through an important interval of turbidite-rich strata overlying the flanks of an oceanic basement high. If time and borehole conditions permit, we will also core and log up to 40 m of basement. The data will provide much-needed constraints on the initial conditions for the "subduction conveyor," which transports the incoming sediments and igneous crust to higher pressure-temperature (P-T) conditions. Ultimately, according to the overarching hypotheses of NanTroSEIZE, the changes imparted on rocks and fluids by those higher P-T conditions drive the onset of seismogenic fault behavior. The architecture of the incoming sediment is also important as a potential control on spatial heterogeneities in permeability, pore pressure, fluid chemistry, and mechanical strength. We will test how and to what extent sandy turbidites in the lower Shikoku Basin facies serve as permeable conduits for draining deeper sections of the underthrust sequence as they pass beneath the accretionary wedge. Focused fluid flow may lead to the development of overpressured compartments, thereby modulating shear strength. In this Scientific Prospectus we present the scientific background and objectives, the drilling operations designed to achieve them, a contingency plan strategy, the currently understood risks and steps taken to mitigate them, and the coordinated stages of the NanTroSEIZE research plan.

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