Influence of fault process zone on ground shaking of inland earthquakes: Verification of Mj = 7.3 Western Tottori Prefecture and Mj = 7.0 West Off Fukuoka Prefecture earthquakes, southwest Japan

Abstract

In this research, we simulate earthquake fault movement by time domain response analysis using the finite element method (FEM), and propose a technique for reproducing the magnitude of shaking at the ground surface level on the basis of this analysis. This technique allows a model to be constructed with only the fault plane size and amount of stress drop as parameters. Moreover, the model accounts for local hypocenter characteristics and spread route characteristics. A process zone related to fault growth for fault rock with fault rupture is known to exist outside the fault. It has been reported that minute cracks form in the process zone; these cracks form as the fault propagates, and the rigidity of rock in the process zone decreases to less than that of the wall rock. In this study, we attempt to incorporate the process zone into an FEM model, and to reproduce past earthquakes by numerical analysis using the proposed method. We test the technique by simulating two large inland earthquakes: the Mj = 7.3 Western Tottori Prefecture earthquake of 2000 and the Mj = 7.0 West Off Fukuoka Prefecture earthquake of 2005, which occurred in southwest Japan. The magnitude of shaking at the ground surface level could be reproduced over the entire analysis area in simulations of these two large earthquakes. In addition, to express the response in the vicinity of the fault with high accuracy, the existence of the process zone must be considered.