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.
Highlights
The Ms 8.0 Wenchuan earthquake on 12 May 2008 caused a significant loss of life and structural damage
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
A 3D Sichuan basin model was first established based on the Quaternary sediment, the near surface layer, the crystalline basin basement, the crustal velocity structure and the real surface topography
Summary
The Ms 8.0 Wenchuan earthquake on 12 May 2008 caused a significant loss of life and structural damage. According to the Modified Mercalli Intensity map (Fig. 1; Yuan 2008), the cities located near the western Sichuan basin edge, such as Dujiangyan, Mianzhu, Anxian, and Jiangyou, suffered severe damage. Zhang et al (2008) simulated the strong ground motion caused by this earthquake considering a three-dimensional (3D) earth structure, finite-fault rupture, and realistic surface topography. A three-dimensional Sichuan basin model is established first by incorporating the realistic surface topography, the Quaternary Chengdu plain, the sediment layer model, the basin crystalline basement, and the 1D crustal structure. The emphasis is put on the cause of the severe damage at the basin edge regions, such as Dujiangyan, Mianzhu, and Jiangyou; the influence of the Quaternary Chengdu plain on the strong ground motion; and the amplification behavior of the Sichuan basin in this earthquake. The wave propagation snapshot, synthetic waveform, distribution of peak ground velocity (PGV) and basin amplification factor are used to analyze the characteristics of the basin strong motion in detail
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