Seismic vulnerability of masonry churches: a geometry-driven quantitative index

Cultural heritage encompasses a wide variety of tangible assets, ranging from archaeological sites and monuments to historical buildings, that represent the memory and identity of communities. Within this broad category, religious buildings constitute a particularly significant subset. These structures, ranging from the early Christian period to the Contemporary era, preserve unique frescoes, mosaics, and sculptures and, in the collective popular perception, represent places of gathering, meeting, and celebration. Their geometrical complexity, the heterogeneity of constituent materials, the construction process, the adopted building techniques, as well as the presence of non-coeval interventions, raise several challenges to the correct structural behaviour analysis toward ordinary and non-ordinary actions. Over the last decades, their physical vulnerability has been investigated through methodologies from different disciplines and at various scales. However, despite the number of studies, only a few have attempted to provide a quantitative evaluation of vulnerability at the regional scale, based on a harmonised definition that allows direct comparison across different types of hazards. The present paper seeks to address this gap by introducing, discussing, and demonstrating the applicability of a quantitative physical vulnerability index for churches to seismic events. The index developed expresses the overall seismic vulnerability of the church as the probability of having a selected failure mode, based solely on geometric indicators, therefore avoiding the need for detailed material or structural characterisation, and offering a simplified yet effective tool for preliminary regional-scale vulnerability analysis.