Evaluation of earthquake-triggered landslides in el Salvador using a Gis based newmark model

Abstract

In this work, a model for evaluating earthquake-triggered landslides hazard following the Newmark methodology is developed in a Geographical Information System (GIS). It is applied to El Salvador, one of the most seismically active regions in Central America, where the last severe destructive earthquakes occurred in January 13th and February 13th, 2001. The first of these earthquakes triggered more the 500 landslides and killed at least 844 people. This study is centred on the area (10x6km) where the most tragic landslide occurred (Las Colinas landslide). The model is based on the Newmark method, which treats a potential landslide as a rigid block sliding on an inclined plane. It requires inputs characterizing the geological conditions and the intensity of earthquake ground motions. The procedure includes factors such as earthquake magnitude, source-site distance, strength of geologic materials, ground water conditions and slope. The data set used in the application includes an earthquake-triggered landslides inventory for the 2001 earthquakes, a 1:100,000-scale geologic map of the region, digital cartography, strong-motion records, data on engineering properties of geologic units, and high-resolution (10 m) digital elevation models of the topography, all of them integrated in the GIS. Displacements of possible landslides along the slope (Newmark displacements) are computed from the Arias Intensity (Ia), and the Critical Acceleration (ac); the latter is inferred from the Factor of Safety (Fs). Newmark displacements have been applied to predict a landslide hazard map at regional scale, in areas where ground-shaking and geological conditions are well known.