Three-dimensional simulations of strong ground motion in the Sichuan basin during the Wenchuan earthquake

Abstract

A three-dimensional model of the Sichuan basin was established by incorporating the Quaternary Chengdu plain, the near surface sediment, the crystalline basement, the 1D crustal velocity structure, and the realistic surface topography of the basin. Based on this model, and by using the spectral-element method and a parallel computing technique, the low frequency (0.05–0.5 Hz) wave amplification behavior of the Sichuan basin during the 2008 Wenchuan earthquake was simulated, and the frequency-related amplification characteristics were investigated. The results reveal that the Sichuan basin significantly amplified low frequency ground motions, with a maximum amplification factor of 9.6 located at the Zhuwa depression, which has the deepest Quaternary sediments. Compared to the vertical component, the horizontal component of the ground motion demonstrates greater amplification factors. The coupling of the basin-edge effect, the rupture directivity effect, and the interference between the waves from different subfaults results in strong local ground motions at the basin edge areas, such as Dujiangyan and Mianzhu. For the studied frequency band, the Quaternary Chengdu plain mainly amplifies seismic waves above 0.3 Hz, while the basin basement is sensitive to waves below 0.3 Hz. The Quaternary Chengdu plain significantly amplifies wave amplitudes and changes the distribution features of strong ground motions.