Numerical Simulation Method of Tsunami Propagation including the Effects of Seafloor Topography

Abstract

For tsunami disaster mitigation, we should predict the arrival time and the run-up height of tsunami. Numerical simulations of tsunami that propagates from the source location to the coast have been widely used to estimate these important parameters. Many simulations, however, mainly focus on the prediction of the first arrival times and the initial height of tsunami. When a tsunami propagates, reflected and scattered waves arrive as later phases of tsunami. These waves are generated by the changes of water depth, and could influence the height estimation, especially in later phases. The maximum height of tsunami could be observed not as the first arrivals but as the later phases, and it is necessary to consider the effects of the seafloor topography on tsunami propagating simulation. It is, however, difficult to simulate the later phases that are important for the tsunami disaster mitigation in the conventional methods. In this study, we investigate the effects of the seafloor topography on tsunami propagation after accommodating the superposition of reflected and refracted waves caused by the changes of water depths in the tsunami simulation with varying water depth. The simulation is performed using the three dimensional in-equally spaced grids with the interpolation of physical parameters in finite difference method (FDM). In the simulation, we import the seafloor topography from the real bathymetry data. We then simulate the propagating tsunami over the changes of the water depth of the sea near the Sendai-Bay. We find that there are some significant features caused by the seafloor topography in our simulated tsunami and the propagation is different from the result by the conventional method. We conclude that the accommodation of the real seafloor topography is indispensable for practical tsunami simulation including later phases, which would be effective for tsunami disaster mitigation.