ABSTRACT

A numerical model was developed for tsunami generation by fully submerged landslide. The model is based on a finite-volume Godunov-type scheme for nonlinear shallow water equations with a source term arising from prescribed bottom motion. The obtained numerical results on the influence of geometric variation in landslide mass revealed that the evolution of depressive wave became significant when the slope of the rear side of the sliding model was steep. The influence of geometric deformation was shown to be generally weak and the distribution of wave height was mostly governed by the shape of the slide in shallow area.

INTRODUCTION

In the past, destructive tsunamis have been induced by submarine landslides over the world (Lovholt et al., 2017). In the offshore area of Norway, for example, submarine landslides have occurred repeatedly and resulting tsunamis are recognized as one of the important natural hazard to coastal areas (Bugge et al., 1988). It is also considered that giant waves were generated in the past around Hawaiian island by underwater landslides (Moore et al., 1994). Recently, the evolution of Papua New Guinea tsunami in 1998 is considered to be influenced by a submarine slide (Tappin et al., 2001). Nevertheless, the existing field observation (e.g., Bondevik et al., 1997; Moore et al., 1994; Tappin et al., 2001) and experimental investigation (e.g., Enet et al., 2002; Grilli and Watts, 2005) on tsunamis induced by submarine landslides are very limited compared with studies on co-seismic tsunamis induced by earthquakes. Accordingly, the characteristics of landslide-generated tsunami evolution over wider range of conditions awaits further investigations. In addition, it is necessary to gain deeper physical understanding on related mechanisms as well as to develop reliable prediction methods in order to design effective counter-measures against landslide tsunamis. For these purposes, numerical approaches are expected to be effective.

In the numerical studies on tsunami generation by submarine landslide, various numerical models have been used such as non-linear shallow water equations, Boussinesq equations, and two-layer flow model (Yavari-Ramshe and Ataie-Ashitiani, 2016). On the basis of these models, the numerical investigations have been successfully applied to various cases recently. In some cases, however, the obtained numerical results are found to be model-dependent (The Tsunami Evaluation Subcommittee, The Nuclear Civil Engineering Committee, Japan Society of Civil Engineers, 2016); Different models might predict different characteristics. Furthermore, the characteristics of landslide tsunamis are related to various features of submarine slide such as geometry, submergence, and kinematic characteristics. The relation among these parameters and tsunami evolution seems to be quite complicated. Previous studies on the relation between tsunami evolution and the characteristics of submarine landslide are, however, relatively scarce. It is therefore important to conduct systematic numerical examination and to enhance physical understanding on the basic characteristics of tsunamis generated by submerged landslides.

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