Permeability in sediments and their role in large slip near the surface of the plate boundary fault in the Japan Trench

Author(s): Tanikawa, W.; Hirose, T.; Mukoyoshi, H.; Tadai, O.; Lin, W.
Author Affiliation(s): Primary:
JAMSTEC, Kochi Institute for Core Sample Research, Nankoku, Japan
Other:
Waseda University, Japan
Marine Works Japan, Japan
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Fluid transport properties such as permeability, porosity, and specific storage are significant parameters that affect earthquake dynamic process. Thermal pressurization model (Mitsui et al., 2012, Earth and Planetary Science Letters) and shallow strong patch model (Kato and Yoshida, 2011, Geophysical Research Letters) were proposed to explain the giant earthquake in the Tohoku area, and transport property around the plate boundary fault is an important factor that impact on both models. Therefore we measured the transport properties of shallow sediments sampled around the plate boundary near the Japan Trench in the IODP expedition 343 at confining pressures up to 40 MPa. The permeabilities of samples from the shallow plate boundary fault at 820 mbsf were very low at 10-20 m2, equivalent to a hydraulic diffusivity of 10-10 m2/s. Permeability in the core of the fault zone at the plate boundary were lower than those in the immediately overlying and underling sediments and the surrounding intact sediment, suggesting that the plate boundary fault can act as a barrier for fluid flow. Low permeability and high specific storage in the shallow plate boundary fault create a strong potential for dynamic fault weakening due to fluid pressurization with frictional heating, even when the initial shear stress is low. Our investigation supports the hypothesis that thermal pressurization on the fault plane induced the extremely large slip in the shallow part of the subduction zone during the Tohoku earthquake. As the fault zone has a lower permeability than the surrounding sediments and a higher clay content, pore pressure generation at depth by dehydration of clay minerals can explain formation of the shallow strong patch on the fault more reasonably than continuous fluid influx from the subducting oceanic crust proposed by Yoshida and Kato (2011, Geophysical Research Letters). Although there are many possible mechanisms of fault weakening, thermal pressurization can act relatively efficiently as slip begins, even at shallow depths. Therefore thermal pressurization is the most likely trigger mechanism for the large shallow displacement of the Tohoku earthquake.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Expedition 343; Expeditions 343/343T; Integrated Ocean Drilling Program; Japan Trench; Japan Trench Fast Drilling Project; Marine sediments; North Pacific; Northwest Pacific; Pacific Ocean; Plate boundaries; Plate tectonics; Sediments; Slip rates; West Pacific
Coordinates: N375619 N375620 E1435449 E1435447
Record ID: 2015001213
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