Risk-oriented seismic microzoning study of an urban settlement

A methodology is presented to evaluate the local seismic response of an urbanized site and to realize cost-effective seismic microzoning studies on a quantitative basis with the aim to provide more insights for the choice of risk mitigation measures. The methodology makes use of an integrated deterministic and probabilistic seismic hazard analysis to select the reference earthquake and the related ground motion used to assess the local seismic response. Amplified response spectra, related to local site effects, are obtained after the investigation of the local geological conditions carried out through integrated geological, geophysical and geotechnical surveys. The amplified response spectra are then converted into reference ones, to match the shape of conventional response spectra provided by many international seismic codes such as Eurocode 8 (Design of structures for earthquake resistance). A vulnerability analysis provided the distribution of the buildings’ typology in the urban centre and allowed for computing the expected damages. The outcome is a zoning of the investigated site matching the correlation between the severity of the expected seismic actions as modified by the local seismic response and the structural features of the buildings present in the urban area. The resulting seismic microzoning is more informative than conventional ones, having the potential to be used for the adoption of risk mitigation measures such as the seismic retrofitting of buildings and the formulation of emergency plans for civil protection purposes.