Near-real-time inference of broadband seismic wavefield considering site effect and frequency nonstationarity

Near-field ground motion from destructive earthquakes is the primary driver of seismic disasters, and its near-real-time inference is essential for damage forecasting, resilience assessment, and emergency response. Interpolation methods based on dense observational records enable rapid ground-motion inference without source parameters, offering substantially faster computation than traditional simulations. However, they typically neglect critical factors such as seismic wave propagation characteristics, the frequency nonstationarity of ground motion, and the local site amplification effects. To address these limitations, this study incorporates the horizontal-to-vertical spectral ratio (HVSR) to correct for site effects in the observed Fourier amplitude spectrum (FAS) and to compensate for site amplification at the target site. For the Fourier phase spectrum (FPS), the equivalent group velocity theory is employed to constrain wave propagation and reconstruct FPS. The inferred FAS and reconstructed FPS are then combined to generate frequency nonstationary ground motion time histories. Validation with real earthquake events demonstrates that accounting for site effects significantly reduces uncertainty in high-frequency ground motion inference. The inferred FAS exhibits improved agreement with observations in terms of amplitude, spectral shape, and predominant frequency within the 0.1 ~ 25.0 Hz range. Additionally, the inferred ground motion intensity measures (IMs) show enhanced consistency with observed values. The proposed method enables broadband seismic wavefield inference within seconds, facilitating rapid scenario construction, disaster digital twins, and near-real-time intensity reporting for earthquake emergency response.