Spectral Characterization of Coastal Tsunami Response in Suruga Bay, Japan, Using Stochastic Simulation Ensembles for Nankai Trough Earthquakes

Coastal tsunami impacts are strongly influenced by local bathymetric features, which can induce resonance and prolong wave activity after the initial arrival. While previous studies have characterized resonant behavior using observations or deterministic simulations, the extent to which such frequency-dependent responses can be systematically related to offshore tsunami characteristics remains unclear. In this study, we investigate coastal tsunami response in Suruga Bay, Japan, using a large ensemble of numerical simulations based on stochastic earthquake source models for the Nankai Trough. For each scenario, we analyze the spectral characteristics of simulated wavefields at offshore and coastal locations and estimate frequency-dependent response functions associated with bathymetric features. These analyses reveal consistent amplification patterns at specific period ranges that are associated with local topography. Building on this, we examine statistical relationships between offshore spectral characteristics and the amplitude of later-arriving coastal waves. The results indicate that certain frequency bands show moderate but consistent correlations with the time-averaged amplitude of post-arrival oscillations, suggesting that offshore spectral information may provide useful indicators of prolonged coastal response under similar source conditions. The objective of this study is not to fully resolve the physical coherence of tsunami sources or nonlinear resonance processes, but rather to provide a statistical framework for linking offshore wave characteristics with site-specific coastal responses. The proposed approach offers a complementary perspective for interpreting tsunami-induced oscillations and may contribute to improving the assessment of prolonged tsunami effects in coastal regions with complex bathymetry.