Historical seismicity and dynamic rupture process of the 2011 Tohoku-Oki earthquake

Abstract

A number of studies have documented the complex rupture process of the M w 9.0 March 11, 2011 Tohoku-Oki earthquake, which is characterized by different stages of rupture, including a large delayed slip near the trench and multiple high-frequency ruptures along the down-dip edge of the seismogenic zone. In this study, a multiscale circular patch model was used to represent the spatial heterogeneity of fracture energy inferred on the plate interface, with spontaneous dynamic rupture simulated by solving the elasto-dynamic equation with a slip-weakening friction law. Historical seismicity, recorded over the past 100 years, was used to determine the spatial heterogeneity of seismic events, with an additional large patch used to model large slip movements near the trench. Dynamic rupture processes qualitatively consistent with observations were successfully modeled during this study, although slight adjustments, including the introduction of foreshock-related stress concentrations, were needed to accomplish this. The delayed failure of the shallow largest patch, representing the main rupture stage, was only achieved by a dynamic nucleation process comprising cascading ruptures within small and moderately sized patches near the down-dip edge of the seismogenic zone; this failure was followed by successive ruptures along the down-dip edge of the zone. This study confirms that a free surface significantly increases fault slip and released seismic moment during an earthquake. In addition, we found that the largest patch occupies the area where the b-value of the Gutenberg–Richter magnitude–frequency relationship is much smaller than 1, while the hypocenter corresponds to a local maximum b-value of about 1.5. This research also suggests that seismicity catalogs can be used to constrain the spatial segmentation of plate boundaries and to propose possible scenarios for the dynamic rupture processes of future earthquakes. ► Historical seismicity data are used to model plate interface heterogeneity. ► Simple model explains complex rupture processes during the Tohoku-Oki earthquake. ► Cascading ruptures of smaller patches work as a dynamic nucleation process.