Coupled simulation of earthquake and tsunami by spectral-element method and effects of bathymetry on oceanic wavefield

The excitation and propagation of multiple wave types, including seismic waves, ocean acoustic waves, and tsunamis triggered by earthquakes within the oceanic wavefield, constitute a problem of substantial scientific and practical challenge for both fundamental geophysical understanding and hazard assessment. While various numerical approaches have been proposed to model these full-coupled wavefields, the role of realistic seafloor topography in modulating wave propagation remains underexplored.

We present a novel earthquake-tsunami coupled simulation approach based on the spectral-element method (SEM), leveraging its robustness and accuracy in representing arbitrary fluid-solid interface geometries. The approach is quantitatively validated through comparisons of simulated permanent seafloor deformation and sea-surface displacement time series with benchmark finite-difference method (FDM) solutions, yielding an excellent correlation coefficient of 0.998 and negligible errors. Furthermore, we construct two distinct numerical models: one incorporating realistic seafloor topography and another assuming an idealized flat seafloor to investigate the effects of bathymetry on oceanic wavefield. Our analyses reveal that complex bathymetry profoundly alters the propagation of both seismic and tsunami waves, modifying amplitudes, arrival times, and spatial distribution patterns. By systematically separating the contributions of the overlying seawater and the underlying seafloor topography, we clarify their individual influences on the composite oceanic wavefield. We also investigate how variations in earthquake source location affect wave propagation waves, underscoring the necessity of accurate bathymetric representation for offshore events.

This SEM-based earthquake-tsunami coupling framework offers a robust tool for comprehensively understanding the oceanic wavefield under gravity and holds considerable promise for advancing earthquake and tsunami risk evaluation, especially when combined with seismological observational data.