Seismic micozoning for the risk mitigation of the monuments in the historical centre of Napoli

Realistic seismograms have been computed at the historical centre of Napoli for the 1980 Irpinia (Mw=6.89±0.09; I=VII-VIII MCS) and the 1688 Sannio (Mw=6.98±0.12; I=VIII MCS) earthquakes. Ground motion for the 1980 event has been computed after validation of synthetics with earthquake recording at about 12 km far from Napoli, that for the 1688 event after validation of synthetics with recording at the historical centre of a moderate (MW=5.2) earthquake from the northern sector of the 1688 fault. The hybrid technique based on the mode summation and the finite difference methods has been used which is fully justified by the good knowledge about the geological and geophysical properties of the neapolitan subsoil. The modeling shows that amplifications of about 2 of peak ground accelerations and of 2-3 for response spectra are to be expected because of the pyroclastic soil cover. The comparison of the response spectra computed for the 1688 earthquake with the Italian seismic building code for Napoli shows that the code is generally adequate for SLV and SLC limit states with respect to the expected effects, even if computed for damping of 5% that is high for the existing tuff brickworks. Instead special care should be taken at sites where the soil cover is thicker as code spectra underestimate the possible ground motion.