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

本研究旨在发展一种更高精度的模拟海啸发生和传播的数值技术，并评估地震断层引起的海底动态位移对海啸的影响。与传统方法相比，我们开发的新方法考虑了海底动力位移和水声波。原则上，本仿真分为两个步骤。前者是采用三维边界元法（BEM）的地震地震动模拟，后者是采用三维有限差分法（FDM）的海啸模拟。这是基于海床-海水系统可以看作是一个弱耦合系统的假设。基于这一假设，考虑地震断裂的破裂机制，首先模拟包括静位移在内的海底动位移。然后，在底部输入与海底位移相关的速度，通过求解Navier-Stokes方程模拟海水扰动。两步仿真的结果不仅用快照表示，而且用动画图形表示，以便于评估仿真的有效性。动态海底位移和声波叠加作用使水波高度显著增加，特别是在近断裂带，这是动、静海底位移叠加作用的结果。此外，本模拟还表明，瑞利波沿海底传播的速度远高于海啸的速度，会引起短周期的水扰动。最后，将该方法应用于近期地震引起的三次实际海啸。从1998年三陆树地震（M6.3）的模拟结果来看，如果断层参数给出的精度较高，该技术能够以令人满意的精度模拟相关海啸。利用地震确定的断层参数对1983年日本海-中部（7.7）地震和1993年北海道-南sei-oki（7.8）地震进行了模拟，结果表明潮汐记录在波高和到达时间上存在很大差异，这主要是由于断层参数和数值模型的粗糙所致。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