Seismic input characterization for some sites in Italy

The seismic input characterization is the first task in the analysis of the seismic behaviour of a structure. The definition of the seismogenetic sources, earthquake catalogue and site characteristics are preliminary to the study. The seismic input may be represented by means of a response spectrum or time-histories. There are many methodologies to produce response spectra and/or input time histories for a given site. The approach may be probabilistic, strictly deterministic or a mixture of both. A strictly deterministic approach is based on the identification of the maximum credible earthquake within an accepted return period. This can be achieved by taking into account both the seismicity historically observed at the site and the features of the seismic sources able to affect the site. The probabilistic hazard assessment is based on Cornell's methodology; it requires the definition of homogeneous seismic sources, their characterization in terms of maximum expected magnitude and Gutenberg-Richter relation (recurrence of events in different magnitude classes) and the choice of an attenuation law for seismic energy, according to the selected ground motion parameter. The methodology proposed by ENEA perform all tasks of the deterministic approach but requires also the comparison between the Fourier amplitudes of the selected time histories with the Uniform Hazard Spectrum (UHS) recovered from the probabilistic approach by means of a statistical index indicating the best fitting. Two case studies are shown