Seismic effects of a small sedimentary basin in the eastern Tibetan plateau based on numerical simulation and ground motion records from aftershocks of the 2008 Mw7.9 Wenchuan, China earthquake

Abstract

In this study, the ground motions that can be attributed to the aftershocks of the 2008 Mw7.9 Wenchuan, China earthquake recorded in the Wudu basin, which is a small basin in the eastern Tibetan Plateau, are analyzed to investigate the seismic effect of a small sedimentary basin. In case of the Wudu basin, the site responses from the basin edge are stronger than those from the basin center; the monitoring sites located near the Wudu basin edge and the Wudu basin center are sensitive to the low-frequency (<3 Hz) and high-frequency (>5 Hz) components of ground motion, respectively. It indicates that some different seismic phenomena occurred in a small sedimentary basin compared with a large sedimentary basin. To further study the ground motion in a small sedimentary basin, a simulation of the Wudu basin was conducted using the finite element method with a viscous–elastic artificial boundary. The grid size of the surface layer of the basin is 2.5 × 2.5 m2, and high-frequency (up to 10 Hz) components of a synthetic waveform were obtained. The simulation denoted that the surface wave initially appeared in the Wudu basin edge and subsequently propagated into its interior. The near-surface soil layers, exhibiting a relatively low wave velocity, magnified the amplitude of the seismic wave in the Wudu basin. Furthermore, the numerical simulation results are basically consistent with the actual ground motion records, especially with the same predominant frequencies of ground motions at the sites located near the Wudu basin edge.