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doi:10.2204/iodp.proc.322.209.2014

Introduction

The Nankai Trough Seismogenic Experiment (NanTroSEIZE) is a multistage drilling project that was implemented to understand the mechanics of subduction zone faulting and earthquakes offshore southwest Japan (Tobin and Kinoshita, 2007). The so-called Kumano transect extends from the Kumano Basin, offshore the Kii Peninsula, across the Nankai accretionary prism and into the Shikoku Basin (Fig. F1). This report focuses on three NanTroSEIZE sites that were drilled during Integrated Ocean Drilling Program (IODP) Expeditions 322 and 333 (see the “Site C0011” and “Site C0012” chapters [Expedition 322 Scientists, 2010a, 2010b] and the “Site C0011,” “Site C0012,” and “Site C0018” chapters [Expedition 333 Scientists, 2012a, 2012b, 2012c]). Site C0011 is located on the northwest flank of a prominent bathymetric high in the Shikoku Basin (Kashinosaki Knoll), whereas Site C0012 is located near the crest of the knoll. Those sites were drilled to document how deposition of the subduction inputs varied as a function of basement topography. Site C0018 is positioned within a small basin on the lower trench slope. That site was cored to study the history of mass transport deposits and the links between sedimentation and fault displacement within the accretionary prism.

We completed constant-rate-of-strain consolidation (CRSC) tests on 33 whole-round samples of mud and mudstone. The purposes of these tests were to quantify sediment compression properties, determine maximum values of in situ effective normal stress, and estimate intrinsic permeability and hydraulic conductivity. The results provide insights into subseafloor fluid flow, consolidation, and dewatering history, as well as the potential for generation of excess pore pressure across a range of depositional environments and facies. The data become more significant when comparisons are made with complementary test results from other sites along the Kumano transect (Dugan and Daigle, 2011; Guo et al., 2011; Saffer et al., 2011).