A two-layer non-hydrostatic landslide model for tsunami generation on irregular bathymetry
Date
2020
Authors
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Publisher
University of Delaware
Abstract
Historically, many significant tsunami events that caused catastrophic damage to coastal communities were triggered by submarine mass failure (SMF). However, landslide tsunamis are less well documented and studied in source mechanism as a fairly new area of tsunami science. ☐ In this thesis, we describe a two-layer, coupled model for water column and landslide motion, developed for the investigation of submarine landslides and resulting tsunami generation over irregular bathymetry. The three-dimensional non-hydrostatic wave model NHWAVE (Ma et al., 2012) is applied as the upper-layer model to simulate landslide-generated tsunami waves. Here, we focus on the derivation and numerical implementation of governing equations for the lower-layer model, where the landslide is described as either a viscous mud flow or a saturated granular debris flow. The governing equations are depth-integrated in a Cartesian coordinate system referenced to the still water level in order to facilitate coupling between water and ground motions. Vertical acceleration of the slide is taken into account by including non-hydrostatic pressure effects within the slide, allowing the model to simulate motions over arbitrary and locally steep bathymetry. A quadratic pressure profile in vertical is imposed to improve the model dispersion property, and a new algorithm of granular rheology closure is introduced where Coulomb rule is applied on local coordinates with x' direction coincident to the flow direction. The model equations are solved using both a Godunov-type finite volume scheme and a finite difference scheme in space and a Runge-Kutta scheme for time integration, and the resulting model is verified in comparison to analytic results and laboratory experiments involving granular slide motion. ☐ A recent landslide-induced tsunami event occurred in the Sunda Straits of Indonesia is investigated in this thesis using the proposed model. Based on the field survey around Anak Krakatau volcano, where a major lateral collapse generated a tsunami causing severe damage to coastlines of Sumatra and Java, numerical simulations are set up with an estimated collapse volume of 0.272 km3 to reproduce observed tsunami characteristics. The simulations consists of a near-field simulation using the 3D two-layer landslide-wave model for landslide tsunami generation and a far-field simulation using the 2D Boussinesq wave model FUNWAVE–TVD for tsunami propagation (Shi et al., 2012). The results from this coupling system agree reasonably well with the field observations.
Description
Keywords
Submarine landslide, Tsunami propagation, Coastal communities, Tsunami generation, Irregular bathymetry, Landslide motion