Dynamic response analysis of cross-fault tunnel considering source-to-structure seismic input and near-fault effect

Tunnels crossing active faults are vulnerable to severe damage under near-fault earthquakes due to the combined effects of co-seismic dislocation and complex ground motion wavefields. To capture the spatiotemporal features of near-fault ground motion and their effects on tunnel structures, this study proposes a physics-based source-to-structure simulation framework. A frequency-wavenumber (F-K) integration method is used to reconstruct broadband seismic wavefields (0.1–10 Hz) based on the finite-fault source model of the 2022 Mw 6.6 Menyuan earthquake. These waveforms are discretized and applied to a nonlinear finite element model of the Daliang Tunnel, which experienced severe damage during the event. The simulated displacement time histories match well with classical finite fault solutions, and the spatial distribution of co-seismic displacements shows good agreement with InSAR observations, especially in amplitude and trend. Within 50 km of the epicenter, the simulated peak ground accelerations (PGAs) agree closely with strong motion records, and the Fourier spectra below 1 Hz are consistent with observed data. Directional velocity pulses and fling-step effects are captured by analyzing PGV/PGA ratios in strike and normal directions, and further confirmed by wavelet transform analysis of near-fault station responses. Structural analysis reveals that fault-crossing segments experience quasi-static shearing dominated by dislocation, while segments farther from the fault are mainly affected by directional velocity pulses. The dynamic stress induced by these pulses accounts for up to 57.1 % of the quasi-static stress. The results highlight the critical importance of low-frequency ground motion components and directional effects in evaluating the seismic response and damage mechanisms of cross-fault tunnels.