Dynamic Source Model for the 2011 Tohoku Earthquake in a Wide Period Range Combining Slip Reactivation with the Short-Period Ground Motion Generation Process

This paper describes a validated dynamic rupture model of the 2011 Tohoku earthquake that reproduces both long-period (20–100 s) and short-period (3–20 s) ground motions. In order to reproduce the observed large slip area (slip asperity), we assign a large Dc (slip critical distance) area following kinematic source inversion results. Sufficiently large slip is achieved through rupture reactivation by the double-slip-weakening friction model. In order to reproduce the strong-motion generation areas (SMGAs), we assign short Dc and large stress-drop areas following empirical Green’s function (EGF) simulation results, which indicate that, although more distant from the hypocenter, SMGA1 ruptured earlier than SMGA2 or SMGA3, which are closer to the hypocenter. This observation is confirmed by the backprojection method. In order to reproduce this important feature in dynamic simulation results, we introduce a chain of small high stress-drop patches between the hypocenter and SMGA1. By systematic adjustment of stress drops and Dc, the rupture reproduces the observed sequence and timing of SMGA ruptures and the final slip derived by kinematic models. This model also reproduces the multiseismic wavefront observed from strong ground motion data recorded along the Pacific coast of the Tohoku region. We compare the velocity waveforms recorded at rock sites along the coastline with one-dimensional (1D) synthetic seismograms for periods of 20–100 s. The fit is very good at stations in the northern and central areas of Tohoku. We also perform finite-difference method (FDM) simulations for periods of 3–20 s, and confirm that our dynamic model also reproduces wave envelopes. Overall, we are able to validate the rupture process of the Tohoku earthquake