Three-dimensional IBEM solution to seismic wave scattering by a near-fault sedimentary basin

Abstract

In this paper, the indirect boundary element method (IBEM) is developed to simulate the three-dimensional (3-D) whole process ground motion in a near-fault complex site. The near-fault large-scale sedimentary basin is investigated as an example by establishing a 3-D kinematic finite fault model and subdomain coupling IBEM. The kinematic boundary conditions of the fault and the continuity of displacement and stress at the interface of the basin are precisely satisfied. The boundary integral equations are solved to obtain the wave fields of each subdomain. The boundary discretization is differentiated by profiling the subdomain wave field to minimize computational cost. The calculation frequency up to 5Hz is achieved on an ordinary workstation. Further, the coupling mechanism of the near-fault and basin amplification effects is discussed in-depth. The influence of the source frequency, fault dip, and fault distance on the basin amplification effect is investigated systematically. The results show that the presence of the sedimentary basin significantly amplifies the near-fault seismic response, especially in the 0 Hz-1 Hz frequency band. The displacement amplitude at the peak frequency (0.22 Hz) inside the basin is amplified 13.11 times compared to that without the basin, while the peak ground displacement (PGD), peak ground velocity (PGV) and peak ground acceleration (PGA) amplify by 1.98 times, 3.42 times and 4.98 times, respectively. The study provides an effective method for simulating 3-D ground motion fields in near-fault complex sites. The conclusions provide an essential reference for seismic risk assessment and seismic zoning in near-fault sedimentary basins.