Physical and numerical modelling of landslide-generated waves

Abstract

Landslide-generated waves are significant threats to coastal areas and lead to destruction and casualties in several locations worldwide. The recent Anak Krakatau subaerial landslide tsunami in December 2018, which resulted in more than 450 deaths, demonstrated the knowledge gap on this subject and motivated this study. Predictive equations are beneficial for estimating the amplitudes and periods of landslide-generated waves in a timely way and can be readily employed for preliminary hazard analysis. Accurate predictions of the amplitude and period of landslide-generated waves is challenging since large uncertainties are associated with landslide parameters. Here in this research, the performance of existing predictive equations is assessed by reproducing past tsunami events, which shows relatively large misestimations. In particular, the predictions made by existing equations were divided by a few orders of magnitude (10–1-104 m). Furthermore, most of these exiting equations need five or six parameters as inputs. This study is focused on developing new predictive equations for estimating the initial maximum wave amplitude and period of submarine and subaerial landslide-generated waves. A comprehensive series of physical experiments (75 tests) in a wave tank at Brunel University London, and numerical simulations (250 simulations) are conducted to provide a large database for developing the new predictive equations. The predictive equations in this study are developed based on non-dimensional parameters, which makes them applicable to real-world landslide cases. These equations require a few landslide parameters (e.g., landslide volume, water depth, and slope angle) to estimate the landslide-generated waves, which is an advantage compared to existing equations. 14 empirical equations are developed for estimating of maximum initial tsunami amplitude of solid-block submarine landslides, two equations for subaerial landslides including solid-block and granular material, one equation for predicting the wave period of subaerial landslide generated waves. This study's predictive equations successfully reproduce laboratory and field data with satisfactory performance. Waves generated by subaerial solid-block and granular landslides are compared in terms of maximum initial wave amplitudes. Results indicate that the maximum initial wave amplitudes generated by solid-block landslides are 107% larger than those generated by granular landslides in our experiments. Also, a critical angle of 60o is achieved for granular slides, and for slope angles more than this critical value, the maximum wave amplitudes start to decrease. It is believed that experimental and numerical investigation of landlside-generated waves, and predictive equations developed in this study have significantly contributed to the knowledge of landslide tsunamis.