CV and Resume

Abstract : Landslide generated tsunamis are natural hazards with important impacts for the populations and infrastructures. Numerical simulations provide a unique tool to capture the dynamics of the granular flows at laboratory and field scale and the generated waves associated to the landslide. Many numerical models have been developed to perform simulations of such events. The main objective of this PhD thesis is (i) to assess the performance and limits of HySEA, a shallow water numerical model, for landslide generated tsunamis and (ii) apply this model to real two cases in volcanic context. We first investigate the different sources of errors linked to the use of this model by quantitatively comparing the numerical simulations with (i) six new laboratory experiments of granular collapses in different conditions (dry, immersed, dry flow entering water) and slope angles, and (ii) the results of the same numerical simulations made with the SHALTOP code that describes topography effects better than most landslide-tsunami models. For laboratory configurations, at the limit of the shallow-approximation in such models, we show that topography and non-hydrostatic effects are crucial. However, by empirically accounting for topography effects by artificially increasing the friction coefficient and performing non-hydrostatic simulations, the HySEA model is able to reproduce the granular mass deposit and the waves recorded at gauges located at a distance of more than 2-3 times the characteristic dimension of the slide, with an error ranging from 1 % to 25 % depending on the scenario, without any further calibration. Taking into account this error estimation, In the context of the on-going seismic volcanic unrest at Montagne Pelée volcano (Lesser Antilles), we calculate the debris avalanche and associated waves for two potential flank-collapse scenarios. Finally, to address landslides and tsunamis hazards related to the seismo-volcanic activity that occurred offshore Mayotte, we combined 2 numerical models: the HySEA code to simulate the flow of the debris avalanche associated with potential landslides and the Boussinesq FUNWAVE-TVD code to simulate the propagation of waves far from the source and the associated flooding. The scenario that represents the greatest threat involve destabilizations on the eastern side of Mayotte's lagoon at shallow depth and can generate a sea surface elevation up to 2m. The tsunami travel time to the coast is very short (few minutes) and the tsunami is not necessarily preceded by a sea withdrawal. This work was carried out within the framework of the REVOSIMA (Réseau de Surveillance Volcanologique et Sismologique de Mayotte) and in close collaboration with the DIRMOM (Délégation Interministérielle aux Risques Majeurs Outre-Mer) and the local authorities.