A Hybrid Method for Modeling Broadband Seismic Wave Propagation in 3D Localized Regions to Incident P, SV, and SH Waves

Abstract

Seismic wave propagation in localized regions plays an important role in the study of seismology and earthquake engineering. However, modeling 3D broadband wavefield of heterogeneous media is computationally expensive and thus has been always a key challenge. In this paper, a frequency wavenumber-spectral element (FK-SEM) hybrid method for modeling broadband seismic wavefield of 3D localized regions is proposed, which obeys the framework of domain reduction, i.e., a finite region is intercepted from a semi-infinite space as the computational domain. To this end, the FK method (based upon the exact stiffness matrix) is first used to calculate the equivalent input of truncated boundaries to incident P, SV, and SH waves with arbitrary angles, and then the SEM is employed to finely simulate the wave propagation process in 3D localized regions. Meanwhile, a viscoelastic artificial boundary is developed in the SEM to realize the absorption of diffracted wavefields generated by internal irregularities. The hybrid method allows the engineering-sensitive high-frequency bands (10–20[Formula: see text]Hz) to be tackled without extra calculations, thereby significant savings computational resources. The correctness and accuracy of the method is verified by four models: a 3D flat stratified site (compared with the FK method), and three typical local sites including 3D canyon, basin and hill topographies (compared with the boundary element method (BEM)). Finally, the method is applied to a realistic case at Zigong Mountain, southwestern China, which suffered extensive topography-induced damages in 2008 Wenchuan earthquake. The results elucidate that the spectral ratio amplification factors predicted by the hybrid modeling are in good accordance with those obtained from strong earthquake data, which further validates the application potential of our method in assisting broadband ground motion research.