Geometrical Effects on Landslide-Generated Tsunamis

Landslide-generated tsunami predictions are commonly based on two-dimensional (2D) wave channel or three-dimensional (3D) wave basin experiments with considerably different outcomes. It is not fully understood which idealized water body geometry applies best to a specific prototype. Hence, a physical small-scale model study has been conducted that, for the first time, systematically investigates the effect of geometry on landslide-generated tsunami height, amplitude, period, and celerity. A rigid slide generated tsunamis propagating in various geometries characterized by the basin side angle $\theta$. Considered were 2D ($\theta =0°$), 3D ($\theta =90°$), and six intermediate geometries. The differences between 2D and 3D wave heights were found to be about 20% at a distance of five times the water depth from the slide impact zone, but increased with increasing distance. It is shown that the 3D case applies on a much wider prototype range than the 2D case because it approximates the wave features on the slide axis for all investigated geometries with $\theta >30°$. The energy flux conservation based on the given 2D results can predict wave heights for the remaining geometries with $\theta \le 30°$. The implications of the present results in practice are discussed and an example illustrates how the results support tsunami hazard assessment despite significant scale effects.