HR: 0800h
AN: S21B-0569    [Abstracts]
TI: Hydraulic and frictional properties of natural clay-rich sediments from ODP Leg190 Nankai Trough and IODP Expedition 311 Cascadia Margin
AU: * Kitajima, H
EM: hkitajima@geo.tamu.edu
AF: Department of Geology and Geophysics, Texas A&M University, MS3115, College Station, TX 77843-3115, United States
AU: Noda, H
EM: nodahiroyuki@kugi.kyoto-u.ac.jp
AF: Department of Geophysics, Division of Earth and Planetary Sciences, Graduate School of Sciences, Kyoto University, Kitashirakawaoiwakecho, Sakyo-ku, Kyoto, 606-8502, Japan
AU: Chester, F M
EM: chesterf@geo.tamu.edu
AF: Department of Geology and Geophysics, Texas A&M University, MS3115, College Station, TX 77843-3115, United States
AU: Shimamoto, T
EM: shima007@hiroshima-u.ac.jp
AF: Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, 739-8526, Japan
AB: Understanding mechanical and hydraulic properties of sediments in accretionary subduction zones undergoing progressive consolidation and localized shear under a wide range of loading rates is crucial to understand the mechanics of subduction earthquakes and accretion processes. We have initiated several suites of experiments to investigate the effects of rate and temperature on mechanical behavior during consolidation and sliding friction using sediment samples recovered from Nankai Trough and Cascadia Margin subduction zones during ODP Leg 190 and IODP Expedition 311, respectively. The experiments include 1) hydrostatic consolidation tests, 2) permeability measurements during consolidation, 3) low-speed friction experiments, and 4) high-speed friction experiments. Several hydrostatic consolidation experiments have been conducted on samples collected from across the proto- decollement zone at ODP Leg190 Site 1173 (360 and 450 mbsf), at elevated pressure and temperature up to 70MPa and 150°C, respectively. Volumetric strain (magnitude of consolidation) increases with the effective pressure and is much greater at higher temperature or after long times, and for the samples taken from above, relative to those from below, the proto-decollement. The pronounced temperature-time sensitivity observed reflects thermally-activated mechanisms of consolidation such as intergranular friction during grain rearrangement, mineral dehydration reactions including the smectite-illite transition, dissolution, and intracrystalline plasticity. Permeability was measured for sediment samples from Nankai and Cascadia under stepwise increasing and decreasing confining pressures up to 70 MPa with a steady-state flow method using Nitrogen gas and water. Permeability varies systematically by confining pressure, sediment type and the collected depth, and pore fluid type. Both low-speed (0.015-15 μm/s) and high-speed (0.1-1.3 m/s) friction experiments were conducted on disaggregated samples from the decollement zone at ODP Leg 190 Site 1174 (839 mbsf). For low-speed friction experiments, 0.2-mm-thick layers were sheared between gabbro blocks in a biaxial-shear apparatus at normal stress of 20-30 MPa. Throughout the experiments, displacement hardening behavior is observed with a friction coefficient ranging from 0.33 to 0.5. The velocity stepping tests show velocity strengthening behavior, with variable b-value; negative b-value is observed at 0.15 μm/s only after the sample experiences the higher slip rate of 15 μm/s. For the high-speed friction experiments, 1-mm-thick layers were sheared between gabbro cylinders in a rotary-shear apparatus at normal stress of 0.3-1.3 MPa. In these tests the initial friction coefficient is approximately 1 and subsequent dynamic weakening is observed only at the slip rate of 1.3 m/s where the friction coefficient drops over 10 m of slip to a steady state value of approximately 0.1. The friction behavior significantly varies with slip rate, and the dynamic weakening during high-speed frictional sliding may be caused by local increases in temperature from frictional heating. All results suggest that both temperature and rate have significant effects on the hydraulic and frictional properties of sediments in accretionary subduction zones.
DE: 5114 Permeability and porosity
DE: 8163 Rheology and friction of fault zones (8034)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: 2007 Fall Meeting