Seismic- and Tsunami-Wave Propagation of the 2011 Off the Pacific Coast of Tohoku Earthquake as Inferred from the Tsunami-Coupled Finite-Difference Simulation

Abstract

Abstract The 2011 Tohoku earthquake ( M 9.0) caused significant hazards including strong ground motion, coseismic ground deformation, and tsunamis. For a deeper understanding of these phenomena, we conducted a large‐scale, parallel computer simulation by means of the finite‐difference method (FDM) with newly developed tsunami‐coupled equations of motion. This method is based on the equations of motion for an elastic medium, treating seawater as elastic material having zero S ‐wave velocity. Tsunami waves are included by taking into account gravity and their equilibrium with the pressure gradient. An effective method of FDM simulation using the state‐of‐the‐art massively parallelized K computer is also studied. With the use of a 3D layered velocity structure that includes topography and bathymetry, basement structure, Moho depth, and plate boundaries, and use of the appropriate source‐rupture model based on joint inversion of seismic waves and geodetic observations, the simulated seismic waves demonstrate anomalous seismic‐wave propagation by the thick 3D basin structure inland. We also found that the sea column acts as a strong absorber of seismic waves for shallow up‐dip slip. On the ocean side, coseismic deformation and tsunamis are dynamically generated in this simulation. Tsunami attacks on the subsided Pacific coast are simulated without any additional assumptions. We also modeled the tsunami and seismic records of ocean‐bottom pressure gauges above the fault. Because sea‐bottom tsunami and seismic observation is powerful but very complex, recording both seismic and tsunami waves, the use of these coupled numerical simulations has great potential for resolving complex source fault rupture processes in a 3D heterogeneous structure. Online Material: Mpeg movies of fault slip, seismic‐wave propagation, seafloor and ground displacement, and tsunamic propagation.