Assessment of earthquake-induced landslides hazard in Quito, Ecuador
Zapata Tapia, Marco Camilo
Magíster en Ciencias de la Tierra
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Quito, the 2.7 million inhabitants growing capital of Ecuador, is placed in an active volcanic and seismic inter-Andean valley. The urban area is built on a 30 km long, 3 to 5 km wide, depression limited by volcanoes, to the east, and by a succession of elongated hills to the west. These hills are the geomorphological expression of the active, local, crustal, Quito fault system, QFS. Seismic hazard is therefore significant (Expected peak ground acceleration, PGA, as high as 0.6 g in hard rock for a 475-year period of return). The urbanization process has been conquering the steep hills, sometimes through and informal land development process, increasing the earthquake landslide risk to population, property and infrastructure. A first, formal, attempt to estimate seismic induced displacements in Quito slopes is presented here. Using updated neotectonic, geomorphological classification, previous landslides susceptibility studies, topographic, microzonation and geotechnical data, seismic induced displacements at 631 natural slopes in the city were calculated using the Bray and Travasarou (2007) equation. Five deterministic earthquake scenarios using two weather conditions (dry/rainy season) were analysed, and the corresponding earthquake induced landslides displacements maps were elaborated. Results highlight areas in which, regardless the seismic scenario, high and very high hazard is always generated, e.g. Pichincha hills, Machangara incision and San Antonio domes and hills. These zones should be considered as a priority to carry out mitigation and also more detailed studies. Areas that present moderate and low hazard in the majority of the seismic scenarios are: Atacazo hills, Panecillo dome and Tectonic uprising Quito-eastern hills. It is expected that maps presented become tools for urban planning and development of mitigation measures in Quito municipality.