| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥300,000)
Fiscal Year 2007: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Fiscal Year 2006: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2005: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
Firstly, we improve the implementation of the fault boundary conditions in the staggered grid finite-difference method by using a fictitious surface to satisfy the fault boundary conditions. In our implementation, velocity (or displacement) grids are set on the fault plane, stress grids are shifted half grid spacing from the fault and stress on the fictitious surface in the rupture zone is given such that the interpolated stress on the fault is equal to the frictional stress. Our implementation has five advantages over previous versions: (1) No leakage of the slip prior to rupture and (2) a zero thickness fault, (3) stress on the fault is reliably calculated, (4) our implementation is suitable for the study of fault constitutive laws, as slip is defined as the difference between displacement on the plane of z=+0 and that of z=-0, and (5) cessation of slip is achieved correctly.
Secondly, we investigated the validity of a method for estimating the critical slip-weakening distance (Dc), w
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hich was proposed by Mikumo and Yagi [2003], for a dynamic rupture model of a recent earthquake. Assuming a uniform distribution of Dc on the fault, we simulated spontaneous dynamic rupture process and generated the synthetic waveforms that would be observed at actual recording stations. Then, we carried out kinematic inversion of the synthetic waveforms and obtained the slip-rate time functions on each subfault. We estimate Dc from these functions and discuss whether the assumed Dc could be recovered correctly. We also investigated the rupture propagation effect over each subfault with a finite dimension and the effects from the waveform inversion and band-pass filtering processes on the estimate of Dc. We found that the propagation effect could cause an apparent correlation between the recovered Dc0-values and the final slip.
It is also important to clarify radiation mechanism of high frequency seismic waves for strong ground motion simulation and for study of physical mechanism of earthquake. Two mechanisms, i.e., stochastic rupture process and stopping phase, had been proposed. When the former mechanism is dominant, high frequency waves must be radiated from inside the asperity. On the other hand, in the case of the latter mechanism, it must be generated from edge of the asperity. In waveform analyses of four inland earthquakes, Japan, Miyake, et. al. (2003) found that the size and position of high frequency rich strong motion generation area coincide with those of asperities. Considering the resolution of the analyses, however, it is not possible to distinguish which mechanism is dominant. The generation area might be along the edge of the asperity or might be inside the asperity. We discussed the mechanism by using computer simulation, especially, which mechanism is efficient. Since seismic wave has usually high frequency components, effective mechanism is more plausible than ineffective one. Less
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