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doi:10.2204/iodp.proc.314315316.218.2011

Introduction

The Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Experiment (NanTroSEIZE) project is a multiexpedition, multiyear complex drilling project aimed at understanding the mechanics of subduction zone faulting and earthquakes through a combination of coring, logging, downhole measurements, and observatory installation, coupled with allied geophysical surveys and laboratory experimental studies (Tobin et al., 2009). As part of operations during NanTroSEIZE Stage 1, core samples were collected at several riserless drill sites for postexpedition laboratory study (Ashi et al., 2009; Screaton et al., 2009a). The compression behavior and hydrologic properties of marine sediments are particularly relevant to the objectives of the NanTroSEIZE project because they exert fundamental control on subseafloor fluid flow, consolidation and dewatering, and the potential generation of excess pore pressures in response to loading by rapid sedimentation and/or tectonic compression.

Here, we report on laboratory consolidation testing of samples collected at IODP Sites C0001, C0004, and C0008 in the vicinity of the “megasplay” fault, a major out-of-sequence thrust (OOST). The fault cuts the accretionary wedge and extends >120 km along strike, and it has been implicated in coseismic slip (Fig. F1) (e.g., Park et al., 2002; Moore et al., 2007). Thus, the megasplay fault is a primary drilling target for the NanTroSEIZE program. Site C0001 sampled the hanging wall of the megasplay fault, and Site C0004 penetrated through the fault into the footwall, which consists of underthrust slope-apron deposits (Expedition 314 Scientists, 2009a, 2009b; Expedition 315 Scientists, 2009b; Expedition 316 Scientists, 2009a). Site C0008 sampled mildly disturbed slope-basin sediments resting above accreted trench-wedge deposits (Expedition 316 Scientists, 2009b). Figure F2 shows the stratigraphic and structural context of all sampling intervals, as well as the dip of bedding in close proximity to the samples.

We obtained 16 whole-round core samples from the drill sites and conducted constant rate of strain (CRS) consolidation tests in order to define (1) sediment compression behavior, (2) the maximum in situ effective normal stress (Pc), and (3) sediment permeability and hydraulic conductivity. Here we report the results of 19 CRS tests, conducted on 16 whole-round core samples (and including three repeat experiments to assess experimental reproducibility) (Table T1). In addition, we conducted quantitative fabric analyses at the University of Missouri (USA) on samples taken immediately adjacent to the CRS test specimens using an environmental scanning electron microscope (ESEM) to image grain fabrics within horizontally and vertically oriented surfaces. Evaluation of microfabric images needs to take bedding dips into account, as shown in Figure F2. We combine results from tests conducted following the same experimental protocols at two institutions: the Rock and Sediment Mechanics Laboratory at The Pennsylvania State University (USA; herein referred to as PSU) and the geotechnical laboratory at the University of Missouri (MU). All notations for this report are summarized in Table T2; sample information and a summary of experimental results are shown in Table T3. Results from fabric analyses are shown in Table T1. Experimental data for each CRS test are provided in CRS in “Supplementary material.”