Numerical investigation on generation and propagation characteristics of offshore tsunami wave under landslide

Abstract

Tsunamis induced by the landslide will divide into a traveling wave component propagating along the coastline and an offshore wave component propagating perpendicular to the coastline. The offshore tsunami wave has the non-negligible energy and destruction in enclosed basins as fjords, reservoirs, and lakes, which are worth studying. The initial submergence condition, the falling height and sliding angle of slider, are important reference indexes of damage degree of landslide and may also matter at that of the landslide-induced tsunami. Depending on the fully coupled model, the effects of them on the production and propagation of the tsunami were considered in the study. Since the slider used was semi-elliptic, the effect of the ratio of the long axis to the short axis was also analyzed. According to the computational fluid dynamics theory, a numerical wave tank was developed by the immersed boundary (IB) method; besides, the general moving-object module of slide mass was also embedded to the numerical tanker. The results indicate that the effects of the squeezing and pushing of the slider on water produce a naturally attenuated wave at the front of the wave train, and the attenuation becomes more serious with the increase in the initial submersion range of the slider. The effects of the vertical movement of the slider cause the increase in the amplitude of the back of the wave train. As the falling height increases, the large wave height increases when the slider is initially submerged and decreases when it is not initially submerged, except for the accidental elevation of that at smaller falling heights. The results also indicate that the hazard of the subaerial landslide-induced tsunami is greater under a small or large falling angle, and that of the partial subaerial and submarine landslide-induced tsunami is greater under a small falling angle. With the increase in the ratio of the long axis to the short axis, the total induced wave energy decreases and the shape of the wave train proportionally reduces, while the wave propagation mode does not change.