Numerical Simulation of Earthquake Generation Cycles before and after the 2011 Tohoku-Oki Earthquake in Northeast Japan

Abstract:

Along the Japan Trench, M7 class earthquakes have occurred in the past. Among them, earthquakes off the coast of Miyagi prefecture have occurred with recurrence intervals of approximately 30-40 years. The M 7.2 earthquake in 2005 is the latest before 2011. On 11 March 2011, the M 9.0 great interplate earthquake occurred off the coast of the Tohoku district (including Miyagi). Currently, it has been passed for more than three years since the M 9.0 earthquake. Post-seismic deformation has continued today, and Off-Miyagi earthquake has not occurred yet.

We numerically simulated cycles for occurrences of seismic and aseismic events along the Japan Trench with the 3D geometry of the Pacific plate using the aging law, which is a type of rate- and state-dependent friction law. We evaluated simulation results achieved using different values of frictional parameters with respect to characteristics such as the slip history and crustal deformation before the Tohoku-Oki earthquake.

Before the Tohoku-Oki earthquake, two slow slip events (SSEs) were observed on 2008 and 2011. The M=7.3 largest foreshock occurred on March 9 [Ito et al., 2013]. Source areas of the mainshock, the foreshock, and the SSEs are in the updip area of the Off-Miyagi earthquakes and post-seismic slip of the M9 earthquake.

By now, we have approximately reproduced some characteristics of observed slips by using several sets of frictional parameter values. In our simulations, M=7.0-7.6 foreshock occurred 0.4~7 days before the mainshock (M=8.6-9.0). And the foreshock occurred within 10 years after the M=7.2-7.3 earthquake at Off-Miyagi. In these models, time interval between the mainshock and the first Off-Miyagi earthquake after the great earthquake tend to be shorter than the average recurrence interval of the past. This tendency was observed at Indonesia. Two M7 class earthquakes occurred before (2002) and after (2008) the 2004 Sumatra earthquake (M9.1). The source regions were at the south end of the rupture zone of the 2004 earthquake and the north end of the rupture zone of the 2005 Nias Island earthquake (M8.6) [Shearer & Burgmann, 2010]. We are now improving our model to reproduce other characteristics. Based on some of the reasonable results achieved, we will discuss possible scenarios for spatial-temporal evolution of slip after M9 class earthquakes.