MPI-OpenMP hybrid simulations using boundary integral equation and finite difference methods for earthquake dynamics and wave propagation: Application to the 2007 Niigata Chuetsu-Oki earthquake (Mw6.6)
Résumé
For the past two decades, the combination between the boundary integral equation method (BIEM) and the finite difference method (FDM) has provided a powerful approach for simulating the dynamic rupture process along a complex fault system and the resultant seismic wave radiation and propagation for the purpose of understanding the physics of seismology and the generation of strong ground motion by large earthquakes. In the many-core architecture currently in use, it can be useful to take advantage of hybrid MPI-OpenMP programming. In this study, we are investigating the Mw6.6, 2007 Niigata Chuetsu-Oki, Japan, earthquake. In the BIEM simulation of the dynamic rupture process, MPI-OpenMP hybrid programming is 24 to 38 % faster than MPI programming on the same resource using 8 to 16 nodes (with 8 cores). In the FDM simulation on the wave propagation, hybrid programming is 25 to 37 % faster. This performance allows us to investigate this earthquake using various parameter settings. First we obtain the frictional parameters based on the proposed kinematic finite source model using BIEM, then model both the spontaneous dynamic rupture propagation and wave radiation by combining BIEM and FDM. It is found that on the given asperities, the peak stress can reach 20 MPa and reduced stress, -20 MPa. Dynamic rupture simulations require a barrier around the southernmost asperity so that this asperity is ruptured in a reverse manner. This effect can be observed very locally in the wave radiation. Furthermore, we observe that the dynamic rupture propagation between two cross-cutting segments generates a more complex wavefield. The change in fault geometry may be dominant over the asperities on a single plane for this earthquake.