Study on estimation of dynamic faulting parameters for strong ground motion simulations

首先，对交错网格有限差分方法中断层边界条件的实现进行了改进，采用虚拟曲面来满足断层边界条件。在我们的实现中，在断裂面上设置速度(或位移)网格，将应力网格从断层移开一半网格间距，并给出破裂带中虚拟表面上的应力，使得断层上的内插应力等于摩擦应力。我们的实现与以前的版本相比有五个优点：(1)断裂前没有滑移泄漏；(2)零厚度断层；(3)断层上的应力计算可靠；(4)滑移定义为z=+0和z=-0平面上的位移之差，适合于断层本构关系的研究；(5)正确地实现了止滑。其次，我们研究了一种估计临界滑移弱化距离(DC)的方法的有效性，w…Mikumo和Yagi[2003]更多地提出了近期地震的动态破裂模型。假设断层上的直流电场分布均匀，模拟了断层的自发动态破裂过程，并生成了在实际记录站观测到的合成波形。然后对合成波形进行了运动学反演，得到了各次断层的滑动速率时间函数。我们从这些函数中估计DC，并讨论假设的DC是否可以正确恢复。我们还研究了有限维子断层上的破裂传播效应，以及波形反转和带通滤波过程对DC估计的影响。研究发现，传播效应会使恢复的Dc0值与最终滑移值之间存在明显的相关性。阐明高频地震波的辐射机制对于强地面运动模拟和地震物理机制的研究也是非常重要的。提出了两种机制，即随机破裂过程和停止阶段。当前一种机制占主导地位时，高频波必须从凹凸体内部辐射出来。另一方面，在后一种机制的情况下，它必须从粗糙的边缘产生。在四次内陆地震的波形分析中，日本、三宅一生等。艾尔(2003)发现高频富强运动产生区的大小和位置与凹凸体的大小和位置一致。然而，考虑到分析的结果，不可能区分哪种机制是主导的。生成区域可能沿着凹凸体的边缘或可能在凹凸体内部。通过计算机模拟对该机制进行了讨论，特别是对哪种机制是有效的进行了讨论。由于地震波通常具有高频成分，有效的机制比无效的机制更可信。较少

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 … More 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