Tsunami hazard assessment in El Salvador, Central America, fromudseismic sources through flooding numerical models.

摘要

El Salvador is the smallest and most densely populated country in Central America; its coast has an approximate length of 320 km, 29 municipalities and more than 700 000 inhabitants. In El Salvador there were 15 recorded tsunamis between 1859 and 2012, 3 of them causing damages and resulting in hundreds of victims. Hazard assessment is commonly based on propagation numerical models for earthquake-generated tsunamis and can be approached through both probabilistic and deterministic methods. A deterministic approximation has been applied in this study as it provides essential information for coastal planning and management. The objective of the research was twofold: on the one hand the characterization of the threat over the entire coast of El Salvador, and on the other the computation of flooding maps for the three main localities of the Salvadorian coast. For the latter we developed high-resolution flooding models. For the former, due to the extension of the coastal area, we computed maximum elevation maps, and from the elevation in the near shore we computed an estimation of the run-up and the flooded area using empirical relations.We have considered local sources located in the Middle America Trench, characterized seismotectonically, and distant sources in the rest of Pacific Basin, using historical and recent earthquakes and tsunamis. We used a hybrid finite differences–finite volumes numerical model in this work, based on the linear and non-linear shallow water equations, to simulate a total of 24 earthquake-generated tsunami scenarios. Our results show that at the western Salvadorian coast, run-up values higher than 5m are common, while in the eastern area, approximately from La Libertad to the Gulf of Fonseca, the run-up values are lower. The more exposed areas to flooding are the lowlands in the Lempa River delta and the Barra de Santiago Western Plains. The results of the empirical approximation used for the whole country are similar to the results obtained with the high-resolution numerical modelling, being a good and fast approximation to obtain preliminary tsunami hazard estimations. In Acajutla and La Libertad, both important tourism centres being actively developed, flooding depths between 2 and 4m are frequent, accompanied with high and very high person instability hazard. Inside the Gulf of Fonseca the impact of the waves is almost negligible.