Dynamic Rupture Simulations Based on the Characterized Source Model of the 2011 Tohoku Earthquake

Kenichi Tsuda,Jun’Ichi Miyakoshi,Jean Paul Ampuero,Hiroaki Uratani,Sachio Ogawa,Takahide Watanabe,Satoshi Iwase

doi:10.1007/s00024-016-1446-1

Abstract

The 2011 Off the Pacific Coast of Tohoku earthquake (Tohoku earthquake, Mw 9.0) occurred on the Japan Trench and caused a devastating tsunami. Studies of this earthquake have revealed complex features of its rupture process. In particular, the shallow parts of the fault (near the trench) hosted large slip and long period seismic wave radiation, whereas the deep parts of the rupture (near the coast) hosted smaller slip and strong radiation of short period seismic waves. Understanding such depth-dependent feature of the rupture process of the Tohoku earthquake is necessary as it may occur during future mega-thrust earthquakes in this and other regions. In this study, we investigate the “characterized source model” of the Tohoku earthquake through dynamic rupture simulations. This source model divides the fault plane into several parts characterized by different size and frictional strength (main asperity, background area, etc.) and is widely used in Japan for the prediction of strong ground motion and tsunami through kinematic rupture simulations. Our characterized source model of the Tohoku earthquake comprises a large shallow asperity with moderate frictional strength, small deep asperities with high frictional strength, a background area with low frictional strength, and an area with dynamic weakening close to the trench (low dynamic friction coefficient as arising from, e.g., thermal pressurization). The results of our dynamic rupture simulation reproduce the main depth-dependent feature of the rupture process of the Tohoku earthquake. We also find that the width of the area close to the trench (equal to the distance from the trench to the shallow asperity, interpreted as the size of the accretionary prism) and the presence of dynamic weakening in this area have a significant influence on the final slip distribution. These results are useful to construct characterized source models for other subduction zones with different scale of the accretionary prism, such as the Chile subduction zone and the Nankai Trough. Dynamic rupture simulations based on the characterized source model might provide useful insights for hazard assessment associated with future mega-thrust earthquakes.

Highlights

Many studies of the 2011 Tohoku earthquake have shown that its rupture process was strikingly depth-dependent: the shallow parts of the fault, near the trench, produced large slip (*50 m) and long period seismic waves (e.g., Suzuki et al 2011) whereas the deep part of the rupture, near the coast, generated smaller slip and strong radiation of short period seismic waves (e.g., Kurahashi and Irikura 2013)
Because the accretionary prism around the Miyagi-Oki area, where the large slip was generated during the Tohoku earthquake, is narrow (Tsuru et al 2002), we considered an additional model with larger accretionary prism, as can be found in other subduction zones
Our simulation results indicate that the large slip observed on the shallow part of the fault arises from the combination of rupture of a shallow asperity with higher stress drop than its surroundings and dynamic weakening processes in the area close to the trench

Summary

Introduction

Many studies of the 2011 Tohoku earthquake have shown that its rupture process was strikingly depth-dependent: the shallow parts of the fault, near the trench, produced large slip (*50 m) and long period seismic waves (e.g., Suzuki et al 2011) whereas the deep part of the rupture, near the coast, generated smaller slip and strong radiation of short period seismic waves (e.g., Kurahashi and Irikura 2013) Understanding such depth-dependent features of the Tohoku earthquake rupture process is important for the estimation of seismic and tsunami hazard caused by mega-thrust earthquakes even in other subduction zones. The ‘‘characterized source model’’ was introduced by Irikura and Miyake (2001) and is

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