ABSTRACT

Three-dimensional experiments and fully nonlinear computations are performed at the University of Rhode Island, to investigate tsunami generation by underwater landslides. Each experiment consists of a solid landslide of idealized smooth shape sliding over a plane slope. Surface elevations are measured using very accurate gages placed at strategic locations. Gage calibration is performed using a newly developed automated system. Landslide acceleration is measured with a micro-accelerometer. The repeatability of experiments is first investigated, and then by varying the initial depth of the landslide, different conditions of wave non-linearity and dispersion are generated and compared. The principle of numerical modeling, using an earlier developed model, is briefly explained. One application is presented and results compared to experiments. The agreement of computations with the latter is quite good. In the model, horizontal velocities are found quite non-uniform over depth above the moving landslide. This would preclude using a long wave model for such landslide tsunami wave generation.

INTRODUCTION

For many coastal areas, underwater landslides represent one of the most dangerous mechanisms for tsunami generation. Whereas tsunamis directly generated by coseismic displacement are generally of small amplitude, and correlate well with moment magnitude, tsunamis generated by submarine landslides are only limited by the vertical extent of landslide motion (Murty, 1979; Watts 1997, 1998). Moreover, underwater landslides can be triggered by moderate earthquakes (Tappin et al, 1999; Tappin et al, 2001) and often occur on the continental slope. Hence, such landslide tsunamis offer little time for warning a local populations. Thus the so-called 1946 Unimak tsunami (Fryer et al., 2001) was generated by a giant underwater landslide (200 km3), triggered by a Msª 7.1 earthquake. The landslide moved down a 4 degree slope from an initial headwall depth of 150 m to the 6000 m depth of the Aleutian terrace.

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