Abstract: Aiming at the three-dimensional ground motion simulation of alluvial basins in urban areas, the unique advantages of boundary element method (BEM) in dealing with wave motion in infinite domain and the high efficiency and large capacity of fast multipole algorithm (FMM) are brought into play. A simulation method suitable for broadband multi-degree-of-freedom model, fast multipole indirect boundary element method (FMM-IBEM) is developed. Through precision comparison and efficiency verification, it is found that FMM-IBEM can accurately and efficiently realize broadband simulation of ground motions in three-dimensional complex sites, and greatly reduce the storage and calculation. Then, the method is used to analyze a three-dimensional alluvial basin with complex shape and undulating bedrock surface in frequency domain and time domain. The results show that: incidence frequency, basin shape and location of the basin have different effects on the magnification of surface displacement of alluvial basins, and generally, the amplification effect in low frequency domain is higher than that in high frequency domain. Spectrum curves show multiple resonance bands, and the magnification effect of surface displacement in the middle and margin of alluvial basin is significantly different. Site selection of important projects should avoid seismic energy accumulation areas in alluvial basins.

Key words: 3D alluvial basin seismic response, FMM-IBEM, seismic wave