Numerical analysis of basin response using Indirect Boundary Element Method (IBEM) for dip-slip sources

Accurate modeling of basin structures and quantitative analysis of basin amplification effects are critical for seismologists and engineers. The Indirect Boundary Element Method (IBEM), developed from the Boundary Element Method (BEM), is particularly well-suited for these tasks due to its capability to manage layers with lateral inhomogeneities. However, current IBEM studies mostly focus on wavefields generated by plane wave incidence or point sources emitting pure spherical P or S waves, which often fail to capture the complex behavior of real seismic events. To address this limitation, we propose an updated IBEM scheme that simulates wavefields from dip-slip sources using the displacement-stress discontinuity vector. We validate this updated IBEM through degenerated models and sources, confirming its robustness in handling dip-slip sources. Further numerical tests reveal several features of basin amplification effects from dip-slip sources: (1) Sources with varying dips cause substantial differences in-basin peak numbers and amplitudes compared to simplified sources. For the surface responses, the ratio of maximum amplitudes (in-basin to out-of-basin) can exceed 10 with asymmetric distributed peaks. (2) The basin amplification effect for dip-slip sources shows similar frequency and velocity contrast dependencies compared to other simplified sources. Our study shows the IBEM scheme is effective and advantageous in basin amplification effect analysis, especially for different source configurations under the same model, with great potential for further applications for seismology, earthquake engineering, and hazard control.