Contrasting hydrological and mechanical properties of clayey and silty muds cored from the shallow Nankai Trough accretionary prism

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doi: 10.1016/j.tecto.2013.01.008
Author(s): Takahashi, Miki; Azuma, Shuhei; Uehara, Shin-ichi; Kanagawa, Kyuichi; Inoue, Atsuyuki
Author Affiliation(s): Primary:
Geological Survey of Japan, Active Fault and Earthquake Research Center, Tsukuba, Japan
Other:
Chiba University, Japan
Toho University, Japan
Volume Title: Great earthquakes along subduction zones
Volume Author(s): Kimura, Gaku, editor; Brodsky, Emily; Di Toro, Giulio; Ide, Satoshi; Kanagawa, Kyuichi; Park, Jin-Oh; Underwood, Michael
Source: Great earthquakes along subduction zones, edited by Gaku Kimura, Emily Brodsky, Giulio Di Toro, Satoshi Ide, Kyuichi Kanagawa, Jin-Oh Park and Michael Underwood. Tectonophysics, Vol.600, p.63-74. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0040-1951 CODEN: TCTOAM
Note: In English. Includes appendices. 40 refs.; illus., incl. 4 tables, sketch map
Summary: Two mud samples cored from the shallow (≈1000mbsf) Nankai Trough accretionary prism at Site C0002 of IODP Expedition 315 are found to be distinctly different in hydrological and mechanical properties. At confining pressures, pore water pressures and temperatures close to their in situ conditions, a clayey mud sample has lower permeability of 2.92×10-19m2, while a silty mud sample has higher permeability of 2.29×10-18m2. Triaxial compression experiments at these conditions and an axial displacement rate of 10µm/s reveal that the clayey mud sample exhibits lower failure strength of 14.2 MPa followed by a slow failure lasting for ≈40 s, while the silty mud sample exhibits higher failure strength of 20.1 MPa followed by a rapid failure within ≈5 s. Friction experiments at these conditions and axial displacement rates changed stepwise among 0.1, 1 and 10µm/s reveal that the clayey mud sample has a much lower steady-state friction (µss≈0.25) than the silty mud sample (µss≈0.53). Although both samples exhibit velocity strengthening, the former has more than three times larger velocity-dependence of steady-state friction than the latter. Such contrasting hydrological and mechanical properties of the clayey and silty mud samples as revealed in this study suggest the following implications for deformation and faulting in the shallow mud-dominant Nankai Trough accretionary prism. Deformation results in a possible increase in pore pressure, and hence, in strength reduction in clayey mud, but not in silty mud. Faulting would preferentially occur in the weaker clayey mud, and its slow failure may result in a slow slip. Faults formed in clayey mud are weak and easily reactivated, but stable and not seismogenic. In contrast, once the stronger silty mud is faulted, its rapid failure may become a seismic slip. Faults formed in silty mud are strong and not easily reactivated, but possibly unstable and seismogenic. Abstract Copyright (2013) Elsevier, B.V.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 06 Petrology, Sedimentary; Accretionary wedges; Active faults; Asia; Cenozoic; Clastic sediments; Clay; Compressibility; Confining pressure; Earthquakes; Expedition 315; Experimental studies; Failures; Far East; Faults; Friction; Geophysical methods; Geophysical surveys; Honshu; Hydrology; IODP Site C0002; In situ; Integrated Ocean Drilling Program; Japan; Kii Peninsula; Kumano Basin; Lithostratigraphy; Mechanical properties; Miocene; Mud; NanTroSEIZE; Nankai Trough; Neogene; North Pacific; Northwest Pacific; P-T conditions; Pacific Ocean; Permeability; Pore pressure; Pore water; Pressure; Quaternary; Sediments; Seismic methods; Seismicity; Shallow depth; Silt; Steady-state processes; Strength; Subduction zones; Surveys; Temperature; Tertiary; Triaxial tests; West Pacific
Coordinates: N331400 N331800 E1364300 E1363800
Record ID: 2014001327
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands