Broadband ground motion simulations applied to the Luding M_S6.8 earthquake on September 5，2022 based on spectral element method

At 12:52 on September 5, 2022, a M_S6.8 earthquake occurred in Luding County, Garze Prefecture, Sichuan Province. The earthquake caused severe damage and heavy casualties in Luding County and its surrounding areas. In order to reproduce the ground motion influence field of the earthquake and analyze the spatial distribution characteristics of near-field ground motion, the deterministic asperity source model is combined with the random source model to obtain the kinematic hybrid source model. Then, the hybrid source model is implemented into the SPECFEM 3D, and the whole-process broadband （0.1−5 Hz） ground motion simulation based on the spectral element method and kinematic hybrid source model is realized. The results from the simulation of Luding earthquake are as follows. Firstly, the simulation results are compared with the time history records of six stations, the corresponding response spectra and the NGA-West2 ground motion attenuation curves to test the applicability of the method. Secondly, the three-component velocity wavefield snapshots of the earthquake is given to demonstrate the directional effect and local site effect of the near field when the seismic wave propagates. Finally, the peak acceleration （PGA） and peak velocity （PGV） maps of the ground motion in the range of 100 km×100 km centered on the Luding area are given, and the spatial distribution characteristics of the ground motion in the near field region for the Luding earthquake are analyzed. Based on the simulation results, the seismic intensity distribution map is given. The results show that the epicenter PGA and PGV is close to 600 cm/s² and 50 cm/s, respectively, and the seismic intensity reaches Ⅸ degree. Due to the influence of mountain-canyon topography in Luding area on the ground motion, the peak of ground motion is significantly amplified at the top of the mountain and the bottom of the canyon, with the amplification of PGA and PGV of 1.9 times and 1.5 times, respectively. The amplification of PGA and PGV at the bottom of the canyon is 1.7 times and 1.4 times. Therefore, attention should be paid to the phenomenon of earthquake amplification and possible secondary geological disasters in mountain-canyon region.