Methodological problems in seismic hazards evaluation for the north-eastern Sicily area

An analysis of seismic hazard was carried out in northeaster Sicily using a program derived from McGuire's procedure, later modified by Saeggesser and Mayer Rosa, for the twin purposes of examining its adaptability to the area of interest and finding its efficiency and limits. On the basis of tests carried out, the main uncertainties in the evaluation of seismic hazard are shown to derive from the degree of subjectivity and from the lack of historical information on the choice and quantification of input parameters. The latter was examined by tests using various combinations of input parameters. The data used were taken from the Catalogue of Italian Earthquakes, assuming V MCS as intensity threshold. The maps of expected maximum intensities produced for return periods between 50 and 500 years, corresponding to different input combinations, show much lower values with respect to the historical maximum observed in the area. This prompted an in depth analysis to redetermine the main input parameters which influence the projection of the expected maximum intensities.