Numerical investigation of landslide-tsunami propagation and transformation in a wide spectrum of water body geometries

Large landslide-tsunamis are caused by mass movements such as landslides and rock falls impacting into a water body. Landslide-tsunami research is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave heights in 2D and 3D vary by over one order of magnitude in the far field and the wave characteristics in intermediate geometries are currently not well understood. This article focuses on numerical landslide-tsunami propagation in the far field to quantify the effect of the water body geometry. The wave model SWASH, based on the non-hydrostatic non-linear shallow water equations, is used to simulate Stokes and solitary waves in 6 different idealised water body geometries. This includes 2D, 3D as well as intermediate geometries consisting of “channels” with diverging side walls. The wavefront length was found to be an excellent parameter to correlate the wave decay along the slide axis in all these geometries in agreement with Green’s law. Semi-theoretical equations to predict the wave magnitude of the idealised waves in any desired point of the water bodies are also presented. The findings herein significantly improve the reliability of preliminary landslide-tsunami hazard assessment in water body geometries between 2D and 3D, as demonstrated with the application on the 2014 landslide-tsunami event in Lake Askja.