IBEM-FEM coupling method for full process nonlinear ground motion simulation of near-fault sedimentary basins

Abstract

Based on the concept of domain reduction, a two-step method combining the indirect boundary element method (IBEM) and the finite element method (FEM) was developed to simulate the full-process ground motion of a 3D (three-dimensional) near-fault complex site. In the first step, the seismic response of dislocation motion in semi-infinite space crust model was accurately solved using the IBEM, which can significantly reduce the dimensionality of the numerical model and easily achieve a computational frequency of 5 Hz on an ordinary workstation. In the second step, considering the inhomogeneity and nonlinearity of soft soils, the seismic wave scattering from a 3D local site was finely simulated using a FEM. The external seismic response obtained through IBEM is converted into equivalent load and transferred to the internal finite element domain, while the PML boundary is applied to absorb the pseudo reflected wave on the truncated boundary. Then, the reliability and accuracy of the method was demonstrated by comparing with the results of existing studies and the traditional IBEM. Further, the proposed coupled method was used to investigate the seismic response of a large near-faulted sedimentary basin. The numerical investigation focuses on four aspects: acceleration histories and response spectra, wave-field snapshot, duration of ground motion, and peak magnitudes and response spectrum of velocity. The results highlight the influence of local site soil non-linearity and medium impedance ratios on the analysis of near-fault seismic response. This research is essential for seismic zoning of complex sedimentary basin sites near faults, and also establishes a “bridge” for seismic design from faults to structures.