Seismic Vulnerability and Simplified Safety Assessments of Masonry Churches in the Ischia Island (Italy) after the 2017 Earthquake

On August 21st 2017 an earthquake of magnitude Mw = 3.9 occurred in the Ischia Island (Italy), causing numerous damages to ordinary and monumental buildings and two casualties. Immediately after the earthquake, teams from the Universities of Napoli Federico II and ‘Parthenope’, carried out inspections on the churches of the island in two phases: the first was developed in the post-emergency and was mainly aimed to assess the overall damage and the usability checks through the A-DC form (MiBACT 2015); the second phase was preparatory to the vulnerability assessment of each church, carried out by filling in the GNDT form (GNDT 2010). Based on the available data, a database made of 27 churches was created to individuate the most representative typologies, to perform a territorial vulnerability assessment, to carry out a detailed analysis of the recorded damages and to construct damage probability matrices. Moreover, for a homogenous class of churches, a predictive formulation of the mean damage was assessed and compared with other formulations available in the literature. Finally, simplified methods for assessing the seismic safety of the inspected churches were applied to the database, in order to confirm the homogeneity of the Ischia churches in terms of seismic vulnerability.