| Budget Amount *help |
¥3,510,000 (Direct Cost: ¥2,700,000、Indirect Cost: ¥810,000)
Fiscal Year 2011: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2010: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2009: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
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| Research Abstract |
Computation of Coulomb stress change(ΔCFF) due to earthquake slip is a powerful tool in order to understand earthquake triggering. However uniform half space is usually assumed in the computation, though highly heterogeneous crustal structures have been estimated in source regions. The purpose of this study is to understand the effect of heterogeneity on the calculation of static stress field. In order to calculate stress field from fault slip in a heterogeneous half space, we solve the equation of motion using 3D finite difference method in which the Lame' constants vary with position and spatial differentiation of these medium properties is taken into account. Since fault slip is represented by double couple force system, we apply equivalent body forces in our finite difference grids(Graves, 1996a). First, we calculated stress andΔCFF field for several simple 2D models to understand easily the effect of heterogeneous medium toΔCFF field. For two-layered medium, stress is amplified on
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the region with higher elastic constants. However, ratio of the stress amplification is less than the ratio of elastic constants between two layers. This is because of interaction between two layers. For simplified basin structure and shallow thrust fault below,ΔCFF increases near the basin but decrease in it. We also discuss the effect of heterogeneity near subducting plate onΔCFF. We found that the subducting plate structure expands the area of positiveΔCFF in the region where outer rise earthquakes occur. Second, we apply to the 2004 Chuetsu(mid-Niigata prefecture) earthquake(Mw6. 6) and four large aftershocks(MJMA> 6). Hikima and Koketsu(2005) and Miyazawa et al.(2005) calculated distribution ofΔCFF for the homogeneous crustal structure and concluded thatΔCFF values just before each aftershocks were positive at the hypocenters of the major aftershocks. However, since the structure is complex in the source region(Kato et al., 2006), it is important to consider the effect of heterogeneity. We used the fault models estimated by Hikima and Koketsu(2005) and 3D structure model by Kato et al(2006) in computation ofΔCFF. The results show that main aftershocks occurred in the area with positive values ofΔCFF. Less
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