Mapping of the seismic tsunami intensity along the coast of Martinique, Lesser Antilles

The tsunami hazard in Martinique due to local, regional and distant seismicity is investigated. Former deterministic scenarios are processed. They were proposed elsewhere based on historical records and the analysis of the morpho-tectonics of the area, i.e., two local subduction scenarios of magnitudes Mw 7.5 and Mw 8.0 representative of the local 1839 earthquake, the regional Mw 7.2-7.5, 1867 Virgin Island event, along with the distant Mw similar to 8.5, 1755 Lisbon earthquake. The tsunami runup and currents are simulated and analyzed. Then, a recent tsunami intensity index is applied and discussed. The modeling of the regional 1867 scenario shows negligible impact on the coast of Martinique which could explain the lack of direct observations in Martinique. Despite a difference of one unit magnitude between the local Mw 7.5 and the distant Mw similar to 8.5 earthquakes, it is found that their tsunami signature for Martinique is nearly equivalent. The local Mw 8.0 event thus controls the tsunami hazard in the island. In the case of this tsunami, whose source is at the east, the western side of the island is not impacted because of wave refraction. Eastward, the coral reef barrier also inhibits tsunami impacts in some sites. Interestingly, it is shown that most of the potentially inundated areas are mangroves that are already subject to daily tidal flooding and seasonal cyclonic activity. They represent an efficient protection against tsunamis. Four occupied locations are however exposed to severe inundation (horizontal penetration of hundreds of meters): Pointe Marin, Le Vauclin, Le Robert and, for the largest, Baie de la Trinite. In terms of current hazard, we have applied two simple procedures to identify sheltered areas for watercrafts: an integrated one, that is easier to use but less accurate, and a direct one, derived from the mapping, which is more complex to implement by end-users but of better precision and efficiency. A large tsunami intensity is obtained at the 4 sites exposed to inundation, possibly yielding severe damages on land and at sea, and which would be extreme at Baie de la Trinite. Even a distant tsunami could impact that site although to a lower extent compared to a strong local earthquake.