Seismic risk at urban scale: the role of site response analysis

A refined seismic risk assessment at urban level is fundamental to identify the most correct risk mitigation policies, both in short and long terms. To date, seismic risk assessment frameworks at regional level consider the site response by means of simplified geotechnical analyses. This study investigates how different procedures of site response analysis influence the risk quantification at urban scale. Simplified and refined analyses are computed and compared for the urban area of Benvento, Italy. For the risk assessment, a stochastic scenario-based approach is adopted, and the risk is quantified in terms of direct losses incurred by the portfolio of buildings in Benevento for a specific historical seismic event, i.e. the 1980 M _w 6.9 Irpinia earthquake. It is demonstrated that simplified approaches for the site response analysis can be unreliable, and the knowledge of the exposure behavior is a key element to appraise the importance of the site response. Finally, a risk-based microzonation is proposed, according to the new philosophy of risk-based hazard maps that may be adopted to achieve an optimal development of the urban areas, ensuring an equal distribution of the risk among the population.