TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 64 (No. 12), pp. 1177-1187, 2012

A scenario for the generation process of the 2011 Tohoku earthquake based on dynamic rupture simulation: Role of stress concentration and thermal fluid pressurization

Yuta Mitsui1, Yoshihisa Iio2, and Yukitoshi Fukahata2

1Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
2Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Uji 611-0011, Japan

(Received December 27, 2011; Revised April 26, 2012; Accepted May 24, 2012; Online published January 28, 2013)

Abstract: We perform dynamic rupture simulations to improve the understanding of the generation process of the 2011 Tohoku earthquake. We assume a dynamic weakening mechanism (dynamic thermal pressurization of pore fluid, hereinafter called TP) on the fault plane to represent nonlinear weakening friction, and take into account the shear stress changes before the Tohoku earthquake, due to the four M 7-class earthquakes that occurred during 2003-2011. To constrain the dynamic rupture simulation, the moment release rate obtained by seismic slip inversions is referred. The simulation result implies the following about the 2011 Tohoku earthquake: (1) The rupture around the hypocenter was enhanced by the stress accumulation due to the preceding M 7-class earthquakes. (2) The enhanced rupture triggered the TP mechanism in the near-trench area causing large slip, which promoted propagation of the rupture over a wide region including the source areas of the M 7-class earthquakes and surrounding conditionally-stable areas. (3) Without sufficient stress accumulation, the moment release of the Tohoku earthquake ended as an M 8-class earthquake. (4) TP in the near-trench area should be effective but moderate. The occurrence time of the next megaquake would be strongly affected by the nonlinear effects of TP and the stress conditions. Thus, our model may contradict the concept of the (quasi-)cyclic occurrence of M 9 earthquakes.
Key words: 2011 Tohoku earthquake, stress accumulation, thermal fluid pressurization, moment-rate function.

Corresponding author E-mail: ymitsui@mail.sci.hokudai.ac.jp

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