Tsunami simulation taking into account dynamic seabed displacement due to seismic faulting

本研究的目的是发展一种数值方法来模拟海啸的产生和传播，以更高的精度，并评估由于地震断层引起的海底动态位移对海啸的影响。与传统的方法相比，我们已经开发的新技术，考虑到海底动态位移以及声波的海啸。原则上，本模拟由两个步骤组成。第一个是地震地面运动模拟的三维边界元法（BEM），第二个是海啸模拟的三维有限差分法（FDM）。这是基于一个假设，即海床海水系统可以被视为一个弱耦合系统。基于这一假设，本文首先考虑地震断层的破裂机制，模拟了海床的动态位移，其中包括静态位移。然后，在底部输入与海床位移相关的速度， ...更多信息 通过求解Navier-Stokes方程，模拟了海水的扰动。两步模拟的结果以快照和动画的形式表示，以便于评估模拟的有效性.发现动态海底位移和声波使水波高度显着增加，特别是在近断层区，由于动态和静态海底位移的叠加效应.此外，目前的模拟表明，短周期的水扰动是由瑞利波，沿沿着海床传播的速度远远高于tsunames.Finally，目前的技术被应用到实际的三个海啸引起的最近的地震。从模拟1998年三陆冲地震（M6.3），本技术被证明是能够模拟相关的海啸到一个令人满意的精度水平，如果故障参数的高精度。利用地震学确定的断层参数对1983年日本海中部7.7级地震和1993年北海道南西冲7.8级地震进行了模拟，结果表明，由于断层参数和数值模型的粗糙性，潮汐记录在波高和到达时间方面存在着相当大的差异。少

The present study aims to develop a numerical technique to simulate generation and propagation of tsunamis with higher accuracy, and to evaluate effects of dynamic seabed displacement due to seismic faulting on tsunamis.In contrast with the conventional one, the new technique we have developed takes into account the dynamic seabed displacement as well as acoustic water waves. In principle, the present simulation is made up of two steps. The first is earthquake ground motion simulation for which the 3-D boundary element method (BEM) is used, and the second is tsunami simulation for which the 3-D finite difference method (FDM) is used. This is based on an assumption that the seabed-sea water system can be regarded as a weakly coupled system. Due to this assumption, the dynamic displacement of the seabed that includes the staticdisplacement is simulated first, considering rupture mechanismof seismic faulting. Then, velocity associated with the seabed displacement is input at the bottom of … More the sea water, and sea water disturbance is simulated by solving the Navier-Stokes equation. Results of the two-step simulation are represented in terms of not only snapshots but also animated figures, in order to facilitate evaluation of validity of the simtulation.The dynamic seabed displacement and the acoustic wave are found to give a remarkable increase in the water wave height especially in the near-fault area, as a result of superposed effects of the dynamic and static seabed displacements. In addition, the present simulation has demonstrated that short-period water disturbance is induced by Rayleigh waves that travels along the seabed with a velocity much higher than tsunamis.Finally, the present technique is applied to actual three tsunamis caused by recent earthquakes. From simulation for the 1998 Sanriku-oki earthquake (M6.3 ), the present technique proves to be able to simulate the associated tsunami to a satisfactory level of accuracy if the fault parameters are given with high accuracy. Simulation for the 1983 Nihonkai-Chubu (7.7) and the 1993 Hokkaido-Nansei-oki (7.8) earthquakes, is conduced by using seismically determined fault parameters and shows considerable difference between tidal records in the wave height and arrival time, mainly because of roughness of the fault parameters s and numerical models. Less