Integrated Simulation of Earthquake Generation and Ground Motion and Tsunami for Nankai Trough Megathrust Earthquakes

We have conducted an integrated simulation of earthquake generation and seismic ground motion and tsunami for realizing a realistic earthquake scenario for large earthquakes along the Nankai Trough in southwest Japan where large earthquakes have repeatedly occurred with the recurrence interval of 100-150 years. The understanding of diversity of the characteristics of the huge earthquakes and their seismic and tsunami hazards are quite important issue. Various earthquake cycle simulations have been recently performed to estimate the diversity of the patterns of the huge earthquakes in the trough and the possibility of the future earthquakes, where the fault rupture propagation process and the friction in a plate boundary are considered. Here, we integrated these two simulations by one-way weakly coupled approach; First we conduct the quasi-dynamic earthquake cycle simulation, then the resultant time-dependent heterogeneous slip histories on the plate boundary are smoothly connected to as inputs of the ground motion and tsunami simulation. As a trial of this approach, the integrated simulation was performed under the huge earthquake scenario with large fault rupture area very similar to the 1707 Hoei earthquake. The target volume of the latter simulation is 1,200 km (EW) x 1,000 km (NS) x 250 km (depth). The equations of motion for viscoelastic body were solved by finite-difference method with discretization of 0.5 km and 0.25 km in horizontal and vertical direction, respectively. For such large-scale simulation the K computer at the AICS, RIKEN was utilized with 2,400 CPUs. The computation time was approx. 1 hour for 80,000 time steps calculation. The results of the integrated simulation show that we successfully reproduced a series of phenomena from earthquake generation to seismic wave propagation, strong ground motion in land, and tsunami growth. Moreover, we confirmed seismic wave generation accompanied by the heterogeneous fault rupture propagation on the plate boundary and the features of the subsequent ground motion on earth surface. It is expected that the high-performance computing of the integrated system enables us to investigate diversity of the seismic and tsunami hazards of huge earthquakes in southwestern Japan as well as their complexity of earthquake generation itself based on physical models.