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Le risque de tsunami dans les Alpes-Maritimes, quelles réalités ? Quelles méthodes d’analyses de l’aléa et de la vulnérabilité ?

Abstract : Tsunamis are complex phenomena that can result from various natural events, such as earthquakes, landslides, or volcanic eruptions. Their amplitude is driven by source characteristics and intensity of the precursor event, continental shelf morphology, and distance to the coast. Although most of tsunamis are located in the Pacific ocean, 15 % of mondial events happened in the Mediterranean Sea (NOAA, 2017). The coastlines of the Alpes-Maritimes are not spared, and have been impacted by two main events : the February 23, 1887 tsunami, which followed the Ligurian earthquake, and the October 19, 1979 tsunami, caused by the collapse of a part of the new harbour construction at the Nice airport. The shoreline of the Alpes-Maritimes concentrates many human, economical, and material assets. Besides, because of the low tsunami frequency, its population is only poorly aware of the associated risk. The presence and the increased development of coastal assets, along with the potential occurence an event, have led the Intergovernmental Oceanographic Commission of the United Nations to call for preparedness for tsunamis in the Mediterranean Sea.Here, risk is defined as the association of a phenomenon occurence, i.e. a tsunami, with the vulnerability of a territory’s assets, the Côte d’Azur coastline. We aim at identifying and characterizing tsunami risk along the French Ligurian Riviera. To do so, we analyze and produce hazard and vulnerability maps using specific methodologies. We first focus on tsunami hazard analysis in the Alpes-Maritimes, identifying and characterizing its magnitude and intensity. Numerical simulations were performed to obtain raw data (runup, current, spatial extent of the flood, etc.). We propose a new tsunami intensity scale combining flood heights, currents and damage to the coast and at sea (biophysical vulnerability). Second, we investigate the territorial vulnerability of the region, concentrating on its main strategic assets and highlighting sensitive areas. We then built on the separate analysis of these two components to assess the coastal tsunami risk. We use two different approaches: the first one is index-based (with three index levels), while the second is normalization-based. This multidisciplinary work, at the confluence between Earth and Human sciences, demonstrates that tsunami risk exists in the Alpes-Maritimes and that it should be integrated in risk prevention and in the gestion of the territory.
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Submitted on : Tuesday, March 23, 2021 - 12:16:26 PM
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Laurie Boschetti. Le risque de tsunami dans les Alpes-Maritimes, quelles réalités ? Quelles méthodes d’analyses de l’aléa et de la vulnérabilité ?. Sciences de la Terre. Université Côte d'Azur, 2020. Français. ⟨NNT : 2020COAZ4050⟩. ⟨tel-03177637⟩

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