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doi:10.2204/iodp.proc.343343T.201.2015

Introduction

The 2011 Tohoku-Oki earthquake (Mw 9.0) and accompanying tsunami were caused by an extraordinarily large coseismic slip (>50 m) on the shallow portion of the subduction zone interface near the Japan Trench (Fujiwara et al., 2011; Ito et al., 2011). A rapid-response drilling operation by the Integrated Ocean Drilling Program (IODP), called the Japan Trench Fast Drilling Project (JFAST) (Expedition 343), drilled through the accretionary prism at IODP Site C0019 to investigate the physical mechanisms and dynamics that enabled the large shallow slip. Site C0019 is located ~93 km seaward from the epicenter of the main shock and ~6 km landward of the Japan Trench (Fig. F1) (Expedition 343/343T Scientists, 2013). Five boreholes were drilled at Site C0019 (Holes C0019A– C0019E), with logging while drilling (LWD) completed in Hole C0019B and coring intervals completed in Hole C0019E. Core samples of the frontal prism and underthrust sediment section were successfully recovered to 844.5 meters below seafloor (mbsf) (Expedition 343/343T Scientists, 2013).

We report on laboratory constant rate of strain (CRS) consolidation and triaxial permeability tests conducted on two whole-round core samples: 343-C0019E-5R-1 (697.18 mbsf), a gray mudstone from Unit III in the frontal prism, and 343-C0019E-20R-1 (831.45 mbsf), a brown mudstone from Unit V in the underthrust section. These tests were designed to characterize the permeability and consolidation behavior under uniaxial and isostatic loading paths over a range of effective stresses. Results of these experiments are then used to estimate in situ hydraulic and mechanical properties of the sediment. This is directly related to the scientific goals of JFAST and will aid in the investigation of the physical controls on large shallow earthquake slip by providing constraints for future numerical models. All notations for this report are summarized in Table T1; core samples and their associated experiment numbers are summarized in Table T2. Experimental data for each uniaxial CRS and triaxial permeability test is provided in Tables T3 and T4 and in TESTDATA in “Supplementary material.”