Numerical modelling of tsunami generation and propagation from submarine slumps: the 1998 Papua New Guinea event

Deep and large submarine slumps may generate tsunamis as disastrous as tsun amis 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 las t 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 be en developed to study the efficiency of deep slumps in producing tsunamis a nd has been applied to the Papua New Guinea event. The landslide is treated as the flow of a homogeneous gravity-driven contin uum 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 resulti ng differential equations are solved by a finite difference method based on shook-capturing. The shallow-water hypothesis is tested by comparison with a model solving Navier-Stokes equations for a mixture of water and sedimen ts. Sensitivity tests carried out for a 2-D Simplified geometry show that t he water surface profile depends strongly on the constitutive law of the la ndslide. The 1998 event is simulated numerically by the shallow-water model, testing different friction laws. The observed inundation height distribution is we ll 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.