Long-Period Ground Motion Simulation of the 2008 Mw7.9 Wenchuan Earthquake Considering the Western Sichuan Basin: Fid-Bau Portal

Long-Period Ground Motion Simulation of the 2008 Mw7.9 Wenchuan Earthquake Considering the Western Sichuan Basin

Liu, Qifang / Yu, Yanyan / Ding, Haiping

This study presents long-period wave propagation simulations of western Sichuan Basin during the 2008 Mw 7.9 Wenchuan, China, earthquake. The simulations utilize a 3D basin model considering unconsolidated Quaternary sediments, and a finite source model inverted from far-field records. The variations of slip amount, rise time, and rake angle of each subfault are directly obtained by inversion. We validate the seismic source and basin velocity models by comparing the synthetic velocity waveforms with observed records at 21 stations inside and outside the basin. Results show that our simulations can reproduce the main features of strong ground motions and seismic damage distributions, as well as high abnormal seismic intensity found at Tangchang town within the basin that are caused by deep and soft deposits. In addition, it is indicated that Sichuan Basin imposed noteworthy influence on wave propagation behaviors inside the basin during this event. First, ground motions are significantly amplified by basin sediments even for long-period waves, with a maximum factor (AF) of more than 8 and 5 for the horizontal and vertical component, respectively. However, no direct relevance between AF and sediment depth can be found. Then, the coupling of low-velocity sediments and interferences of delayed seismic waves radiated from different locations of large fault greatly change the strong ground motion distributions, and lengthen the strong shaking durations. In addition, vertical component ground motions are less affected by basin sediments compared with horizontals. Our study indicates that a higher-resolution source and basin velocity models are necessary for local strong ground motion prediction or seismic hazard analysis in the future, and seismic response of large-scale basins under successive rupture process deserve special attention.