Numerical Simulation of Tsunami Generation by Cylindrical Seabed Motion Using an Axisymmetric Boundary Element Method

Introduction: Localized, vertically dominant seabed deformations, such as submarine volcanic eruptions and underwater earthquake, can trigger devastating near-field tsunamis characterized by strong three-dimensional (3D) radial spreading. Accurately modeling this initial wave generation phase is critical for elucidating energy transfer mechanisms and predicting near-field hydrodynamics for coastal hazard assessment.

Methods: This study develops a specialized axisymmetric Boundary Element Method (BEM) to simulate fully nonlinear water waves generated by impulsive seabed deformations. By solving Fully Nonlinear Potential Flow equations in a reduced 2D domain, the model preserves exact 3D radial geometric spreading while achieving orders-of-magnitude computational efficiency compared to full 3D Computational Fluid Dynamics (CFD) models. The numerical model is rigorously validated against laboratory experiments and high-fidelity OpenFOAM simulations.

Results: A systematic parametric study reveals that the wave generation process is controlled by the coupling of the source aspect ratio and uplift duration. Small-scale sources are dominated by a "radial drainage" mechanism where energy is lost to lateral flow during slow deformations. Conversely, large-scale sources exhibit a "bulk uplift" mechanism, maintaining a high relative wave amplitude independent of the duration. Furthermore, while wave amplitude scales linearly with seabed stroke, fully nonlinear simulation captures critical secondary wave dynamics.

Conclusions: The proposed axisymmetric BEM provides a highly efficient and robust framework for evaluating near-field tsunami generation. The findings demonstrate that while linear theory is adequate for creeping motions, fully nonlinear modeling is indispensable for accurately assessing the hazards of localized, high-acceleration seabed events.