Seismic hazard and design earthquakes for the central archaeological area of Rome

In order to evaluate the seismic input suitable to be used for the microzonation of the central archaeological area of Rome, two different approaches were used: Probabilistic and Deterministic Seismic Hazard Assessment (PSHA, DSHA). For PSHA, three Uniform Hazard Spectra and three design spectra, derived from the literature and the Italian regulations, were considered. For DSHA two possible design earthquakes were selected: one having a magnitude 5.5 and a distance 20 km and the other having a magnitude 7 and a distance 85 km. The choice of these two scenarios was supported by the analysis of historical and instrumental seismicity, by the study of the surrounding faults, and by the disaggregation of the seismic hazard. The standard PSHA, based on seismogenic zones with uniformly distributed seismicity used for the Italian hazard map and building code, results in higher values with respect to DSHA (PGA of about 0.12 g and spectral maximum of around 0.35 g), unless an appropriate fraction of the standard deviation of the attenuation relationship is considered in the deterministic analysis. Recorded accelerograms, corresponding to the magnitude-distance couples selected using the DSHA were also included in the analysis. The seismic input was represented in terms of acceleration response spectra and time histories.