Vulnerability and Seismic Exposure of Residential Building Stock in the Historic Center of Alcamo

The influence of exposure evaluation methodology in the assessment of the seismic vulnerability of the residential building stock in the historic center of Alcamo, a town of 45,000 inhabitants in Western Sicily (Italy), hit by an earthquake in 1968, is evaluated in this study. A comparison of exposure estimates on the basis of the description of the residential building stock according to two different approaches is performed. The first, typical of seismic vulnerability assessment procedures at a territorial scale, refers to the description of residential building stock through an accurate typological description, conducted using the CARTIS survey form. The form allows for a detailed description and survey of the prevailing ordinary building types within areas characterized by the homogeneity of the building fabric in terms of age of construction, structural characteristics, construction techniques, and distribution of types. The detailed description of building types allows for the assessment of exposure at the municipal scale based on an estimate of the total number of units and the percentage of each type within each compartment, obtained by interviewing local technicians. The second is based on a similar survey at the building scale, namely, drawing up a form for each building. The comparison of exposure and damage scenarios obtained with the two methods proves that the approximations provided by the compartment-scale survey are compatible with the purposes of an assessment of vulnerability and damage scenarios at the territorial scale.