Numerical Simulation of Strong Ground Motion for the Ms 8.0 Wenchuan Earthquake of 12 May 2008 With Realistic Surface Topography

The Wenchuan earthquake of 12 May 2008 is the most destructive earthquake in China in the past 30 years in terms of property damage and human losses. In order to understand the earthquake process and the geo- morphological factors affecting the seismic hazard, we simulated the strong ground motion caused by the earthquake, incorporating three-dimensional earth structure, finite-fault rupture, and realistic surface topography. The simulated ground motions reveal that the fault rupture and basin structure control the overall pattern of the peak ground shaking. Large peak ground velocity (PGV) is distributed in two narrow areas: The one with the largest PGV values is above the hanging wall of the fault and attributed to the locations of fault asperities and rupture directivity, the other is along the northwestern margin of the Sichuan Basin and caused by both the directivity of fault rupture and the amplification in the thick sediment basin. Rough topography above the rupture fault causes wave scattering, resulting in significantly larger peak ground motion on the apex of topographic relief than in the valley. Topography and scattering also reduce the wave energy in the forward direction of fault rupture but increase the PGV in other parts of the basin. These results suggest the need for a localized hazard assessment in places of rough topography that takes into account of the topographic effects. Finally, had the earthquake started at the northeast end of the fault zone and ruptured to the southwest, Chengdu would have suffered a much stronger shaking than it experienced on 12 May, 2008.