Spectral-element simulation of the earthquake-tsunami coupling and bathymetry effects on oceanic wavefields

SUMMARY 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. This phenomenon involves complex interactions of waves within a fluid-solid coupled system, which is critical for both fundamental geophysical understanding and enhancing hazard assessment. While several numerical methods have been developed to simulate the full wavefield, few studies have systematically explored the crucial influence of complex seafloor topography on coupled wave dynamics. This study introduces a novel earthquake-tsunami coupling simulation method within a 2-D spectral-element method (SEM) framework, leveraging its flexibility to handle complex geometries and accuracy for long-range wave propagation. To validate the accuracy of the simulated seismic waves, ocean acoustic waves, and tsunamis, we quantitatively evaluate the permanent seafloor displacement, yielding a high correlation coefficient of 0.997 and a negligible error of 5 × 10−3 compared with the analytical solution. The mean relative error of the calculated tsunami phase velocities of the proposed method with those from the propagator matrix method is only 0.12%. Furthermore, we establish two distinct numerical models—one incorporating irregular bathymetry and another with an idealized flat bathymetry—to systematically investigate the effects of bathymetry on the oceanic wavefield. Our results demonstrate that the irregular bathymetry significantly influences the propagation characteristics of both seismic waves and tsunamis, altering wave amplitudes, travel times, and spatial patterns. We further decompose the contributions of seawater and seafloor geometry, highlighting their respective roles in shaping the overall wavefield. Additionally, we examine the influence of varying earthquake source locations on wave propagation paths, emphasizing the importance of accurately modelling bathymetry for offshore seismic events. Overall, our proposed 2-D earthquake-tsunami coupling simulation framework provides a powerful tool for comprehensively understanding the oceanic wavefield under gravity and offers significant potential for improved earthquake and tsunami hazard assessment, particularly when combined with seismological and oceanographic observations.