Two-dimensional non-hydrostatic two-layer model for the generation and propagation of submarine landslide tsunamis

Tsunamis generated by submarine landslides typically have short wavelengths, making non-hydrostatic effects significant during both generation and propagation. Conventional two-layer flow models based on the long-wave theory, which are widely used for simulating such tsunamis, neglect these non-hydrostatic effects. In high-fidelity modelling, tsunami generation is often simulated using a three-dimensional fluid model, which is then transformed into a two-dimensional model to simulate the subsequent propagation. To overcome these drawbacks, we developed a non-hydrostatic two-layer model capable of consistently simulating both the generation and propagation of submarine landslide tsunamis. The model incorporates a non-hydrostatic generation filter to smoothly transfer the debris-layer displacement to the seawater layer at each time step and includes Boussinesq-type dispersion terms for the seawater layer to account for wave dispersion. This model was applied to a submarine landslide source inferred from a seafloor scar located off the southwestern coast of Japan. Furthermore, the motion of the debris layer computed using the two-layer model was extracted and applied as a boundary condition in the three-dimensional fluid model. Tsunami waveforms produced by the two models exhibited excellent agreement, thus validating the accuracy of the proposed model. Non-hydrostatic effects play a critical role in the early stages of tsunami generation and propagation, influencing wave shape and amplitude. Although three-dimensional fluid models offer high accuracy, they are computationally intensive and may encounter stability issues in high-resolution inundation modelling. The proposed model provides an efficient and practical framework to simulate the generation, propagation, and run-up processes of tsunamis caused by submarine landslides.