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On the 16th of October 1979, a part of the Nice new harbour extension, close to the Nice international airport (French Riviera), slumped into the Mediterranean Sea during landfilling operations. A submarine slide with initial volume close to seashore of about 10 millions m 3 , which could have evolved later into an avalanche, was followed by a small tsunami, noticed by several witnesses in the ''Baie des Anges.'' The maximum tsunami effects were observed 10 km from the slide location near Antibes city, which was inundated. Previous analyses used rough approximate methods and produced models which did not conveniently fit data. In this paper, both the slide and the generated water waves are numerically simulated on the basis of the shallow water approximation. The landslide is assimilated to a heavy Newtonian homogeneous fluid downslope under gravity. Water waves are generated by sea-bottom displacements induced by the landslide. Taking into account a very accurate multibeam bathymetric map, the Nice slide of 10 millions m 3 is simulated by this model. The numerical results are generally consistent with the observed hydraulic local effects in front of the Nice airport, however they are not in agreement in the far field. A larger and deeper landslide 2 km off Nice airport is tested to quantitatively study the effects of the landslide volume on water waves generation.

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Abstract.The

SUMMAR YDeep and large submarine slumps may generate tsunamis as disastrous as tsunamis of tectonic origin. Such a landslide is likely to be the origin of the 1998 July 17 tsunami of Papua New Guinea, the deadliest tsunami in the last 50 years. Water waves devastated a 20 km stretch of coastline, wiping out three villages and killing more than 2200 people. A numerical model has been developed to study the efficiency of deep slumps in producing tsunamis and has been applied to the Papua New Guinea event.The landslide is treated as the flow of a homogeneous gravity-driven continuum governed by a rheological law. Water waves are generated by sea-bottom displacements induced by the landslide. The shallow-water approximation is adopted for both the landslide and the associated water waves. The resulting differential equations are solved by a finite difference method based on shock-capturing. The shallow-water hypothesis is tested by comparison with a model solving Navier-Stokes equations for a mixture of water and sediments. Sensitivity tests carried out for a 2-D simplified geometry show that the water surface profile depends strongly on the constitutive law of the landslide.The 1998 event is simulated numerically by the shallow-water model, testing different friction laws. The observed inundation height distribution is well reproduced by the model for a volume of 4 km 3 , with its top located at a water depth of 550 m, and sliding with a Coulomb-type friction law over a distance of 5 km.