An exposure model capturing the geographical distribution and main characteristics of the building stock exposed to seismic hazard is a fundamental step in earthquake risk assessment and reduction. In this context, an open exposure model for the residential building stock has been developed for the Andean Countries (Argentina, Bolivia, Chile, Colombia, Ecuador, Peru and Venezuela), as part of the South America Risk Assessment (SARA) project. This initiative was supported by the Global Earthquake Model (GEM) Foundation and the SwissRe Foundation, and involved more than 20 local institutions, such as the Pontificia Universidad Católica del Perú (PUCP), Fundación Venezolana de Investigaciones Sismológicas (FUNVISIS), Pontificia Universidad Católica de Chile (PUCC), Escuela de Administración, Finanzas y Tecnología (EAFIT – Colombia) and the Escuela Politécnica Nacional (EPN – Ecuador).
The model was constructed using population and housing census data from the national statistical offices of each country, and the judgment from dozens of local researchers and practitioners. Information concerning number of buildings, dwellings and occupants, the structural characteristics (e.g. construction materials, lateral load resisting system, range of number of storeys), average built-up area, and replacement costs were included for the smallest administrative level available in the national census.
Regarding building classes and construction materials in the Andean region, it was found that masonry construction represents 55% of the entire building portfolio (unreinforced, confined and reinforced masonry represent 31%, 22% and 2%, respectively), followed by 17% of reinforced concrete buildings, 13% of earth/adobe houses (mostly concentrated in Bolivia and Peru) and 8% wooden structures (mostly located in Chile). The remaining 7% is distributed across steel, stone and unknown typologies (1%, 2% and 4%, respectively).
This model shows that the Andean countries are characterized by a large concentration of population and buildings in urban areas. In fact, 50% of the residential building stock is located in only 15 regions: Buenos Aires, Bogota, Lima (and Callao), Santiago, Medellin, Caracas, Cordoba, Rosario, Cali, Guayaquil, Maracaibo, La Paz, Quito, Santa Cruz, Valencia. From these regions, Lima, Santiago, Caracas, Cali, Guayaquil, Quito and Valencia are the most populated cities located in high seismic areas (with an estimated peak ground acceleration (PGA) larger than 0.20g for a 475 years return period) representing 17.4% of the exposed portfolio. Furthermore, it has been estimated that 35% of the population in the Andean region is exposed to moderate or high seismic hazard.
Organisations and individuals that are interested on assessing and identifying seismic risk in South America can utilize the proposed exposure model for different geographical levels. As part of the SARA project, the model was used to calculate probabilistic seismic risk in the region, as well as seismic scenarios (e.g. Bogota, Medellin, Cali, Lima and Quito). Moreover, the model can be also used, to some extent, for risk assessment considering other type of hazards (i.e. tsunami, landslides, liquefaction and floods).
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