Methodology for an effective risk assessment of urban areas: progress and first results of the merisur project

The progress and results the MERISUR, Methodology for an Effective RISk assessment of URban areas, are presented. This project aims at developing an effective methodology for urban seismic risk assessment that provides solutions to some deficiencies detected after recent damaging events worldwide, including risk mitigation actions based on benefit/cost ratios. In a fisrt stage, the hazard and vulnerability models are developed and improved. A procedure to determine the hazard-controlling seismogenic fault, contsistent with different probability levels, is established. Methods to include active faults as individual sources and to consider near filed effects that significantly amplify ground motions are proposed. A more complete description of seismic vulnerability encompassing structural, non-structural components is accomplished. Vulnerability modifiers to incorporate effects or urban parameters on vulnerability classes are also quantified. A distinction is also made between damage to structural and non-structural building elements. For this purpose, a pushover analysis is specifically carried out to model building response and damage trends on non-structural elements. This gives the primary damage. In addition, the area covered by the resulting debris is also estimated both in inner spaces (within the building) and in the outer space (public roads and streets). In this way, a volume of debris will be associated to each area unit of the city, and the potential damage to persons and elements exposed, such as urban furniture and vehicles, will be assessed. This constitutes the secondary damage. A static level of occupation (building, urban furniture, etc.) and a dynamic level of occupation (persons, vehicles) will be assigned to each area unit of the city, hereby defining the exposure in time and space. Earthquake losses related to primary damage of building components and to secondary damage (such as urban furniture and vehicles) will be also assessed. Cost/benefit ratios between ex ante risk mitigation measurements will be developed in order to decide whether risk transfer or risk retention is preferable for different risk scenarios. This analysis will confer effectiveness to the results of a seismic risk study. Overall, the estimate of earthquake losses and cost/benefit ratios are topics with little presence in the scientific literature concerning damaging earthquakes in Spain. Thus, the results of this study will provide effective solutions to the challenge to society tackled in this proposal