Generation of New Cracks Accompanied by the Dynamic Shear Rupture Propagation of the 2000 Tottori (Japan) Earthquake

The 2000 Tottori (Japan) earthquake caused fracture zones of surface rupture at some places away from the trace of the main causative fault. In order to explain this observation, the 3D dynamic rupture process of the 2000 Tottori (Japan) earthquake was simulated. The attractive feature of the problem under consideration is the possibility of introducing internal new cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation. The discrete element method was used to solve this problem because it can introduce internal tensile cracks. For the shear rupture propagation the simple slip-weakening model was used as a friction law on the fault. The new tensile cracks occur, following the classical Griffith theory, when the critical value of tensile fracture surface energy has been reached. The first step to solve the problem was the estimation of the dynamic parameters, such as stress drop, strength excess, and critical slip, which were recovered from the results of waveform inversion. In the second step, a shear dynamic rupture process was simulated assuming that shear slip occurs only on the preexisting fault, and the tensile stress concentration resulting from shear slip causes the new cracks that propagate away from the pre-existing fault. The results, which are consistent with the observations, show a free-surface rupture caused by the new cracks and the development of a flowerlike structure springing from the borders of the pre-existing fault and main asperity.