NUMERICAL SIMULATION OF WAVE PROPOGATION IN THE GRENOBLE BASIN: BENCHMARK ESG2006

ABSTRACT- Numerical simulations of wave propagation in the Grenoble basin are undertaken using the finite difference method (FDM) in a staggered grid framework (4th order in space) for an elastic medium with a flat ground surface and perfectly matching layer absorbing boundaries. The seismic source is introduced in the form of a seismic moment tensor irrespective of whether a point source or expanding finite source model is used. This is the same methodology adopted in our previous studies (Aochi and Douglas, 2006; Douglas et al., 2006). As the FD grids in our code are equally spaced in both horizontal and vertical directions, the grid size should be fine enough to describe the Grenoble Basin where a low velocity (300m/s) zone is present near the surface (a few 100 m depth at maximum) while the surrounding bedrock has a velocity ten times higher. We carry out the simulations with different resolutions (a grid size of 100 m and of 50 m). Both of them require high performance computation resources. This benchmark test is an interesting application for seismic hazard evaluation because of the high contrast basin structure and its non-negligible dimensions. For the two large earthquake scenarios (S1 and S2 of magnitude 6), our numerical simulations are compared with empirical ground-motion models for peak ground velocity (PGV) to validate the calculations and to evaluate the local effec