Simulation of tsunami propagation with space-varying seafloor topography

Tsunami is generated by a sudden deformation of the seafloor, such as uplift and subsidence, caused by fault motion of an earthquake below the seafloor. Numerical simulation of tsunami propagation is frequently used to predict the arrival time and the order of magnitude of the inundation for disaster mitigation purposes. In the propagation process, reflected waves are generated by the change in water depths and influence the tsunami height estimation, in particular in the later phases. In this study, we try to simulate tsunami propagation to accommodate the 2-D varying seafloor topography. In our simulation code, we assume water as a non-viscous fluid. A finite difference method (FDM) is employed using three equations; the equations of continuity, motion, and barotropy. In this study, we simulate the tsunami generation by a sudden change in the water depth and the propagation, using the Pearson approximation to accommodate the spatially varying water depth. We impose the seafloor topography on the basis of the 500m-mesh bathymetry data that JODC (Japan Oceanographic Data Center) provides. We assume a domain included in the data region and simulate tsunami. By using this method, we are able to see not only the propagation velocity due to the change in the water depth, but also reflected waves at the same time. The calculation method that we use in this study can simulate both the tsunami propagation and the reflection that are strongly influenced by the real topography of the seabed. Depending on the accuracy of the simulation, we think the present study can be extended to simulate the tsunami behavior of the later phases that often cause severe tsunami hazard for far-travelling tsunamis once the seafloor topography has been well measured.