A two-layer granular landslide model for tsunami wave generation: Theory and computation

•A new two-layer model for granular landslide motion and tsunami wave generation is developed.•The model is validated by the laboratory measurements of impulse waves generated by 2D/3D granular landslides.•The model reasonably predicts the tsunami wave generation by granular landslides.•The model can capture granular landslide motion from initiation to deposition.

We develop and test a new two-layer model for granular landslide motion and tsunami wave generation. The landslide is described as a saturated granular flow, accounting for intergranular stresses governed by Coulomb friction. Tsunami wave generation is simulated by the three-dimensional non-hydrostatic wave model NHWAVE, which is capable of capturing wave dispersion efficiently using a small number of discretized vertical levels. Depth-averaged governing equations for the granular landslide are derived in a slope-oriented coordinate system, taking into account the dynamic interaction between the lower-layer granular landslide and upper-layer water motion. The model is tested against an analytical solution for granular dam-break flow and 2D and 3D laboratory experiments on impulsive wave generation by subaerial granular landslides. Model results illustrate a complex interplay between the granular landslide and tsunami waves, and they reasonably predict not only the tsunami wave generation but also the granular landslide motion from initiation to deposition.