Landslide Tsunami Amplitude Prediction in a Numerical Wave Tank

Abstract

Tsunami generation by underwater landslides is simulated in a three-dimensional (3D) Numerical Wave Tank (NWT) solving fully nonlinear potential ow equations. The solution is based on a higher-order Boundary Element Method (BEM). New features are added to the NWT to model underwater landslide geometry and motion and specify corresponding boundary conditions in the BEM model. A snake absorbing piston boundary condition is implemented on the onshore and o shore boundaries. Results compare well with recent laboratory experiments. Sensitivity analyses of numerical results to the width and length of the discretized domain are conducted, to determine optimal numerical parameters. The (3D) e ect of landslide width on tsunami generated is then estimated. Results show that the 2D approximation is applicable when the ratio of landslide width over length is greater than three. INTRODUCTION Tsunamis generated by underwater landslides triggered on the continental slope appear to be one of the major coastal hazards for moderate earthquakes (e.g., Tappin et al. 2001). Such tsunamis, indeed, are only limited in height by the landslide vertical displacement, which may reach several thousand meters (Murty 1979; Watts 1998). Hence, huge coastal tsunamis, o ering little time for warning, can be produced (Watts 2000). Predicting landslide tsunamis requires complex numerical models in which both landslide and bottom geometry must be accuratedly represented. The models must also account for nonlinear interactions between landslide motion and surface wave eld. Grilli and Watts (1999) implemented such of a twodimensional (2D) numerical model, based on a higher-order Boundary Element Method (BEM), i.e., a NumericalWave Tank (NWT). Reviews of the literature to Dept. of Ocean Engng., University of Rhode Island, Narragansett, RI 02882, USA. E-mail: grilli@oce.uri.edu. Applied Fluids Engng., Inc., Mail Box #237, 5710 E. 7th Street, Long Beach, CA 90803, USA. E-mail: phil.watts@applied uids.com