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Low Coseismic Shear Stress on the Tohoku-Oki Megathrust Determined from Laboratory Experiments

2013; American Association for the Advancement of Science; Volume: 342; Issue: 6163 Linguagem: Inglês

10.1126/science.1243485

1095-9203

Kohtaro Ujiie, Hanae Tanaka, Tsubasa Saito, Akito Tsutsumi, James Mori, J. Kameda, E. E. Brodsky, F. M. Chester, Nobuhisa Eguchi, Sean Toczko,

Geological and Geochemical Analysis

Large coseismic slip was thought to be unlikely to occur on the shallow portions of plate-boundary thrusts, but the 11 March 2011 Tohoku-Oki earthquake [moment magnitude (Mw) = 9.0] produced huge displacements of ~50 meters near the Japan Trench with a resultant devastating tsunami. To investigate the mechanisms of the very large fault movements, we conducted high-velocity (1.3 meters per second) friction experiments on samples retrieved from the plate-boundary thrust associated with the earthquake. The results show a small stress drop with very low peak and steady-state shear stress. The very low shear stress can be attributed to the abundance of weak clay (smectite) and thermal pressurization effects, which can facilitate fault slip. This behavior provides an explanation for the huge shallow slip that occurred during the earthquake.