Strength characteristics of Japan Trench borehole samples in the high-slip region of the 2011 Tohoku-Oki earthquake

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doi: 10.1016/j.epsl.2014.12.014
Author(s): Ikari, Matt J.; Kameda, Jun; Saffer, Demian M.; Kopf, Achim J.
Author Affiliation(s): Primary:
University of Bremen, Center for Marine Environmental Sciences, Bremen, Germany
Other:
Hokkaido University, Japan
Pennsylvania State University, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.412, p.35-41. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 48 refs.; illus., incl. sect., sketch map
Summary: The 2011 Tohoku-Oki earthquake demonstrated that the shallowest reaches of plate boundary subduction megathrusts can host substantial coseismic slip that generates large and destructive tsunamis, contrary to the common assumption that the frictional properties of unconsolidated clay-rich sediments at depths less than ∼5 km should inhibit rupture. We report on laboratory shearing experiments at low sliding velocities (<1 mm/s) using borehole samples recovered during IODP Expedition 343 (JFAST), spanning the plate-boundary decollement within the region of large coseismic slip during the Tohoku earthquake. We show that at sub-seismic slip rates the fault is weak (sliding friction µs=0.2-0.26), in contrast to the much stronger wall rocks (µs>3DF0.5). The fault is weak due to elevated smectite clay content and is frictionally similar to a pelagic clay layer of similar composition. The higher cohesion of intact wall rock samples coupled with their higher amorphous silica content suggests that the wall rock is stronger due to diagenetic cementation and low clay content. Our measurements also show that the strongly developed in-situ fabric in the fault zone does not contribute to its frictional weakness, but does lead to a near-cohesionless fault zone, which may facilitate rupture propagation by reducing shear strength and surface energy at the tip of the rupture front. We suggest that the shallow rupture and large coseismic slip during the 2011 Tohoku earthquake was facilitated by a weak and cohesionless fault combined with strong wall rocks that drive localized deformation within a narrow zone. Abstract Copyright (2015) Elsevier, B.V.
Year of Publication: 2015
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 19 Geophysics, Seismology; 30 Engineering Geology; Boreholes; Clay minerals; Cohesionless materials; Coseismic processes; Decollement; Diagenesis; Displacements; Earthquakes; Expedition 343; Expeditions 343/343T; Experimental studies; Fault zones; Faults; Friction; IODP Site C0019; Integrated Ocean Drilling Program; Japan Trench; Japan Trench Fast Drilling Project; Laboratory studies; Mechanical properties; North Pacific; Northwest Pacific; Pacific Ocean; Rock mechanics; Rupture; Shear; Shear strength; Sheet silicates; Silicates; Slip rates; Smectite; Subduction; Tohoku-Oki earthquake 2011; Wall rocks; West Pacific
Coordinates: N375619 N375620 E1435449 E1435447
Record ID: 2015026474
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands