MACROSEISMIC ANALYSIS OF ENVIRONMENTAL EFFECTS INDUCED BY JANUARY AND FEBRUARY 2001, EL SALVADOR EARTHQUAKES (RIESCA project)

This paper deals with the analysis of the numerous environmental effects caused by the two devastating earthquakes that struck El Salvador (Central America) on January and February 2001. This dataset has been the basis to evaluate earthquake sizes through the ESI intensity fields, and to compare them with the traditional damage-based macroseismic scales. The 13 January 2001 earthquake occurred off the coast of El Salvador (Mw 7.7; h 60 km) killing more than 900 people, 4723 injured and more than 17,000 missing according to official statistics, and caused a tremendous damage in nearly 280,000 houses. Severe damage and great loss of life was mainly due to the earthquake-induced landslides. More than 5,000 landslides and extension cracks were recorded over an area of 25,000 km2 in El Salvador. Especially the Las Colinas landslide (200,000 m3) had devastating consequences (600 dead). On February 13, a strike-slip earthquake (Mw 6.6; h km) shook the central part of El Salvador causing extensive damage over concentrated areas, 315 dead and 3,400 injured people. The quake has been associated with the reactivation of the San Vicente segment of the El Salvador Fault Zone, a major regional seismotectonic structure. This event triggered additional thousands of landslides over an area of ca. 2,500 km2, among which two very large scale landslides: Rio El Desague, 1.5 million m3, and Rio Jiboa, 12 million m3. Soil liquefactions and lateral spreads, were also recorded in alluvial plains and coastal flats. The evaluation of the coseismic effects by means of the ESI-2007 Scale has allowed: (1) a detailed picture of both macroseismic fields (200 points), (2) to test earthquake intensity with size and areal distribution of induced landslides, (3) to refine earthquake intensity in sparsely populated zones, (4) to estimate epicentral Intensity (I0), and (5) collection of useful data for seismic zonation.