3D physics-based ground motion simulation and topography effects of the 05 September 2022 MW6.6 Luding earthquake, China

On September 5, 2022, a MW6.6 earthquake occurred in Luding, Sichuan Province, which caused a large number of casualties and serious damage to infrastructures. To represent the strong ground motion of the destructive shock, the SPECFEM 3D code is adopted to model the wave propagation and a hybrid kinematic source to model the fault rupture. As for the hybrid fault source, spatial heterogeneities aimed to simulate the high-frequency radiation are added to a prescribed asperity model used to generate the low-frequency part. With a conforming mesh of the established 100 km × 100 km × 60 km numerical model and the developed hybrid fault source, the maximum resolved frequency of the simulation is 5 Hz. First, the numerical model is validated by comparing the simulated results with the six recorded waveforms as well as the corresponding Spectral acceleration and Fourier amplitude spectra. Then, the wave fields and Synthetic seismograms are presented to investigate the velocity pulse-like ground motion in the near-fault region. Finally, the topographic effect on the ground motions is identified by comparing the results from the numerical model with (Topo) and without topography (Flat). It is demonstrated that the simulated ground motion well reproduces the near-fault fling-step effect and the wave scattering effect caused by the surface topography. The hill-canyon topography significantly amplifies the surface motion, with the amplification factors (Topo/Flat) of PGV at the peak of Gonggashan mountain and at the bottom of Daduhe river reach 1.9 and 1.4, respectively. Moreover, the PGV amplification factor is in good correlation with the topography's elevation, indicating that the topographic amplification can be predicted by establishing the relationship between amplification factor and elevation.