Abstract:

When we are able to evaluate earthquake-induced stress changes of the ground around ruptured faults and adjacent faults, it will be possible to improve the prediction accuracy of the magnitude and probability of future earthquakes. Generally, the interaction between active faults is represented by static Coulomb stress changes (ΔCFF) induced by fault rupturing. In most cases, ΔCFF is calculated based on the elasticity theory of dislocation; there are few studies where it is calculated by 3D-FEM. In this study, we conducted fault rupture simulations using 3D-FEM for simple models with a planar fault plane and homogeneous bedrock and examined the influence of fault type and initial stress distribution. As a result, ΔCFF calculated by 3D-FEM became considerably larger than that calculated by the elasticity theory of dislocation. Moreover, even when a fault type and seismic magnitude were the same, the distribution domain and quantity of ΔCFF differed greatly owing to the combination of analytical parameters.

1 Introduction

When we are able to estimate earthquake-induced stress changes of ground around ruptured faults and adjacent faults, it will be possible to evaluate rupture propagation and improve the prediction accuracy of the magnitude and probability of future earthquakes. Generally, the change of stress before and after an earthquake is evaluated by static Coulomb stress change (ΔCFF) (Stein et al. 1997, Toda et al. 1998, Hashimoto 1996). ΔCFF has been applied to earthquake-forecasting indexes that have been used to assess potential hazards related to earthquake activity. Seismic activities are enhanced by slight ΔCFF increases of 0.1 MPa (Toda et al. 1998). Examination by dynamic ΔCFF, i.e. Coulomb stress change during an earthquake, has been carried out recently, and there is a report that dynamic ΔCFF distribution matches aftershock activities than static ΔCFF distribution well (Kilb et al. 2002, Gomberg et al. 2003). However, in those studies, ΔCFF was calculated from static or dynamic stress changes using the assumed dislocation on the fault plane; the dynamic destruction process was not taken into account.

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