Vulnerability and Seismic risk scenarios based on GIS techniques: application to Barcelona city (Spain)

Abstract

The exponential increase in the world’s population, together with the growth of big cities, which is characterized by the inadequate occupancy of the soil, contributes augment the damage due to seismic catastrophes. The high concentration of population, buildings, in-frastructures and valuables exposed, turn these zones into high risk areas. Most of earth-quake casualties are due to buildings collapsing, that is some 90% of direct deaths. The current study contributes to the development and application of the seismic risk assess-ment in big cities. In this work, a brief description of the namely Vulnerability Index Method (VIM) for assessing seismic damage scenarios in urban areas is presented. This method considers five non null damage states, characterizes the seismic action in terms of macroseismic intensity and buildings by means of a vulnerability index. The estimated damage degree is measured by a semiempirical function relating mean damage factor to intensity and vulnerability index. Damage Probability Matrices (DPM) for a given seismic scenario are obtained by assuming a binomial or beta-equivalent probability distribution. The VIM has been used to analyse the vulnerability of the dwelling buildings of Barcelona (Spain) and to develop earthquake scenarios for the city. Then, the specific residential buildings of Barcelona are classified in different groups characterized by a similar seismic behaviour. Therefore, all buildings belonging to each typology are cast in the most prob-able class according to vulnerability. In this way, the average vulnerability index is associ-ated to each building typology of Barcelona and it is refined later on the basis of behaviour modifiers. In order to apply this method to Barcelona a deterministic (historical event) and a probabilistic (10% occurrence probability in 50 years) earthquake are used to assess expected damage. In both cases the effects of soil are taken into account. The obtained results showed the peculiarities of individual buildings and were highly con-sistent with the historical and modern evolution of the populated area and with the charac-teristics of soils, demonstrated the solidity of this method. In both scenarios the average damage state is moderate. The damage to the population is significant and its evaluation depends strongly on casualty models. In this sense, it is necessary to consider the spe-cific numerical values as a prediction of the order of magnitude of the evaluated quanti-ties. The seismic risk scenarios at different scales have been of inestimable help to guide the action and decision making in seismic risk prevention and mitigation in the city. Another of the significant contributions of this research is the creation of a powerful and versatile tool, whose design is based on Geographic Information Systems (GIS). Throughout the years, detailed information on the design of buildings has been obtained by collecting and completing a highly complete and reliable GIS database of the dwellings of the city of Barcelona. It has been used to obtain very detailed vulnerability maps and damage scenarios of the entire city at different levels: buildings, census tracks, neighbourhoods and districts. On the other hand, this type of software is essential to map georeferenced scenarios, which are useful to highlight and discriminate the strong and weak points of its social and residential urban network.