Correlation between earthquake damage and seismic site effects: The study case of Lentini and Carlentini, Italy

On December 13th 1990 a magnitude 5.6 seismic event, felt throughout Sicily, and having maximum seismic intensity VII-VIII, occurred. Although, it is classified as moderate magnitude, it caused causalities and the collapse of a few buildings. Two of the most struck cities were Carlentini and Lentini, located in south-eastern Sicily at about 20 km from the instrumental epicenter. In order to evaluate the influence of ground features on the damage distribution, both vulnerability and damage maps were drawn using information collected in about 6000 forms coming from official ascertainments. Significant damage observed in some portions of the investigated areas, appears related to the modest quality of the buildings that were classified as medium to high vulnerability. To evaluate the role played by the geologic setting, two sites were instrumented to measure shear-wave velocity of the main lithotypes. Sixty-three ambient vibrations measurements were also performed both in free field and inside some buildings. Moreover, using information coming from geological and geophysical surveys, 1D numerical modelling were done to achieve information about the main ground motion parameters. The results highlight the occurrence of significant site effects and the potential presence of resonance phenomena between site and structure during the occurrence of a seismic event. Seismic site amplifications together with the buildings' vulnerability, observed through damage surveys, contributed to enhance the inherent seismic risk of the investigated area.