COMPARISON OF THE RECORDED SEISMIC SIGNALS FOR THE 2012 EMILIA AND 2016 CENTRAL ITALY SEISMIC SEQUENCES WITH THE DESIGN EARTHQUAKES BASED ON THE PSHA APPROACH

The recent seismic sequences occurred in 2012 in the Emilia region and in 2016 in Central Italy have confirmed the high level of vulnerability typical of masonry historical buildings and historical centres. Among these, the historical centre of Amatrice was razed to the ground and most of the historical buildings of municipalities in the epicentral area suffered partial or total collapse. Ground motion recordings highlighted a remarkable difference with the design earthquakes provided by the national seismic hazard map, which is based on the PSHA (Probabilistic Seismic Hazard Assessment) approach. Specifically, the response spectra of the signals recorded at Finale Emilia and Mirandola (2012) and at Norcia and Amatrice (2016) have been compared to the design spectra prescribed by the national building code; from comparison, the strong underestimation of the design spectral accelerations is evident, especially for the historic centre of Amatrice, due to the additional effect of local amplification. All recent Italian earthquakes (L'Aquila 2009, Emilia 2012, Central Italy 2016) and many others around the world, have shown that the PSHA approach does not provide reliable results in case of severe events. On the contrary, the technical literature shows that the NDSHA (Neo-Deterministic Seismic Hazard) approach generally provides reliable results. The need to update the seismic regulations, therefore, is clear in view of a preventive policy against the collapse of historic centres and monuments, based on the correct definition of seismic hazard levels. In the present contribution the analysis of the above seismic events is presented, being part of a wider analysis on the effects produced on the built heritage by seismic sequences.