The study of the influence of terrain on ground motion is quantified as the amplification effect of terrain on ground motion. In this paper, we use the spectral element method to simulate the three-dimensional real terrain model, and select the aftershocks of the station ground motion observation records in the Lushan area as the source, and analyze the amplification effect of the three-dimensional topography on the ground motion of the Lushan earthquake in the low frequency range (1-5hz). In this paper, the Fourier model of the real terrain of Lushan and the half-space free model are used to calculate the Fourier amplitude spectrum. The results show that in the low frequency range, the ground fluctuations have a large variation, which will have complex effects on the propagation of seismic waves. Especially in the bulging mountain and depression terrain, the time course peak is large. In addition, this paper selects the mountain near the BXD station from the calculation area, and analyzes the terrain magnifying effect of the convex mountain. Under 2-3hz, the mountain slope near the source side has a magnification effect of 3-4 times.
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