A broadband ground motion simulation method based on probabilistic seismic hazard defined earthquakes and hybrid source models

The complex rupture process of a seismic source can result in intricate ground motion characteristics in near-fault regions (hanging wall effects, directivity effects, and pulse effects). Both domestic and international regulations stipulate that for major engineering projects, it is essential to consider the specific seismic environment and the target hazard level of the site, and to adopt site-specific ground motions. In light of this, this study proposes a novel probabilistic-deterministic hybrid seismic ground motion prediction method that combines the advantages of both probabilistic and deterministic approaches. The proposed method first employs a decomposed probabilistic approach based on CPSHA (Chinese probabilistic seismic hazard analysis) to calculate seismic activity and hazard, yielding a scenario earthquake with probabilistic significance. Subsequently, a hybrid broadband ground motion simulation method considering a hybrid source rupture model is employed on the fault rupture mechanism and site-specific seismic impact field. Low-frequency (≤1 Hz) ground motions are simulated using the spectral element method (SEM), while high-frequency (>1 Hz) ground motions are simulated using a modified three-component stochastic finite-fault method, and then combined with the deterministic low-frequency results. In the high-frequency simulation, a GP15.4 hybrid kinematic source model is adopted to account for high-frequency random scattering, together with a nonlinear sedimentary layer analysis module. As a case study, the method is applied to a critical structure in Baodi District, Tianjin, with a natural period of 1s, under a rare seismic event. This study illustrates and validates the rationality and advancement of the proposed method for seismic design of important buildings and structures in near-fault regions. The results demonstrate that this new method is more reasonable compared to traditional artificial ground motion synthesis methods based on uniform hazard spectra, and it effectively exhibits significant near-fault effects. The site-specific probabilistic ground motion of major projects near faults is in accordance with the code requirements. The study has significant value for urban planning, near-fault seismic disaster simulation, seismic risk assessment, and reducing seismic risks for critical engineering projects in active fault zones.