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doi:10.2204/iodp.sp.315add.2007

Introduction

The three expeditions that make up NanTroSEIZE Stage 1 operations (Expeditions 314, 315, and 316) are designed to log, core, and measure boreholes along a transect across the Nankai Trough subduction zone from the oceanic plate through the accretionary prism and into the forearc region. The original sites chosen for drilling are intended to investigate the character of sedimentary inputs, faulting, and fluid flow at the toe of the accretionary prism; the geometry and mechanical characteristics of faults and sediments in the megasplay system; and the character and history of the sediments deposited into the Kumano Basin. The overarching goal of this project is to understand the character, evolution, seismogenic potential, and current behavior of sediments, faults, and fluids along this subduction margin.

Because of the large number of sites chosen for drilling and the wide variety of potential challenges to drilling in this area (ranging from weather and currents, sediment/borehole stability, methane hydrate deposits, and/or potential gas or fluid overpressure), an array of alternate sites has been designated for contingency operations. As the processing and interpretation of the high-resolution three-dimensional (3-D) seismic data have progressed, the specific locations, depths, and potential challenges associated with particular scientific targets have been refined. The factors detailed above have required several minor changes and additions to the planned operations, which are outlined in this addendum to the Expedition 315 Scientific Prospectus (Ashi et al., 2007).

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