2001 EL SALVADOR EARTHQUAKES, IMPLICATIONS FOR SEISMIC HAZARD ASSESSMENT

The earthquake sequence occurred in El Salvador between January and February 2001 has been considered one of the most destructive event occurred in El Salvador in the last fifty years. It began with the devastating earthquake of January 13 (Mw7.7), located 40 km from the coast, in the subduction zone of Cocos-Caribbean plates, with a focal depth of 60 km. Exactly after a month, on February 13, another destructive earthquake (Mw 6.6) was located 30 km inland. From San Salvador, inside the Caribbean plate at a shallower focal depth of about 10 km. The 13 February earthquake was associated to the local fault system aligned with the Central America Volcanic Arc. The January and February 2001, El Salvador, earthquakes were related the former to subduction along a submarine seismic structure, and the latter to an onshore seismic structure. Both quakes caused severe damage especially due to wide and abrupt landslides phenomena. Thousands of landslides of different type and size were triggered, particularly in the coastal mountain ranges and along the volcanoes in the Great Interior Valley. Liquefaction phenomena and lateral spreading were widely observed along coastal area; fractures were observed alone and/or in conjunction with other geological effects. The landslides were the most extensive and destructive among the secondary effects and caused most of the human deaths, especially after. the 13 January earthquake (Las Colinas landslides killed about 600 persons). The slides severely damaged the main lifelines (roads, aqueducts, power lines, etc.), engineered structures, as well as coffee plantations. The most affected area by the earthquake effects was prevalently located in a sparsely inhabited volcanic environment. Thus, the possibility of applying the common macroseismic intensity scales, based on damages to buildings, as well as the effects on humans and objects, was limited to a few settlements and villages. The ongoing study presented here describes the geological-geomorphological environments affected by both earthquakes and defines the earthquake intensity by taking into consideration the occurrence, size and areal distribution of earthquake environmental effects. Indeed, this study can significantly improve the evaluation of seismic intensity, which still remains a critical parameter for a realistic seismic hazard assessment, allowing to compare historical and modern earthquakes.