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

Abstract

Abstract. 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 differencesfinite 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 5 m 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 4 m are frequent, accompanied with high and very high person instability hazard. Inside the Gulf of Fonseca the impact of the waves is almost negligible.

Assessment of tsunami hazards for the Central American Pacific coast from southern Mexico to northern Peru

“…As expected in subduction zones, the main focal mechanism of the earthquakes in the trench is thrust and inverse (Álvarez Gómez, 2009), but also strike-slip earthquake occurrences are recorded. It is remarkable how common outer-rise normal earthquakes are here, occurring in larger proportions than in several other subduction regions (Álvarez Gómez et al, 2012).…”

“…The southern ECA seismicity is due to the interaction of three main tectonic plates, namely Nazca, Caribbean and South American plates, and several microplates, like the Panama and North Andes plates at their boundaries (Bommer and Rodriguez, 2002). As expected in subduction zones, the main focal mechanism of the earthquakes in the trench is thrust and inverse (Álvarez Gómez, 2009), but also strike-slip earthquake occurrences are recorded. It is remarkable how common outer-rise normal earthquakes are here, occurring in larger proportions than in several other subduction regions (Álvarez Gómez et al, 2012).…”

“…A completeness analysis based on a method introduced by Albarello et al (2001) was applied to the AMB-AD-NOAA earthquake catalogue in the zones 1, 2 and 4. The method consists of the following steps.…”

“…It was established that the ECA region was affected mostly by moderate events, but also by some destructive tsunamis (see e.g. Fernández et al, 2000Fernández et al, , 2004Álvarez-Gómez et al, 2012) and that all countries in the ECA are likely to be hit by tsunami waves in the future. Preliminary tsunami hazard estimations were performed on the Pacific coast in 2000 by the Centro de Investigaciones Geofísicas (CIGEFI) de la Universidad de Costa Rica, the Red Sismológica Nacional (RSN: ICE-UCR), the Instituto de Sismología, Vulcanología, Hidrogeología y Meteorología de Guatemala and the Institute of Solid Earth of the University of Bergen, Norway.…”

“…In a very general sense, this is the type of result that is expected from what is usually referred to as probabilistic tsunami hazard analysis (PTHA). In the last decade or so, PTHA approaches have been discussed, among others, by Geist and Parsons (2006), Power et al (2007), Álvarez-Gómez et al (2013). In the more general understanding, PTHA combines statistical techniques, usually derived from the seismological research field, with advanced tsunami inundation modelling.…”