New Developments in Seismic Risk Assessment in Italy

The paper illustrates some improvements in the seismic risk assessments in Italy and describes the differences deriving from the use of different approaches to calculate the losses and the influence exerted by different hazard results. The first method of risk evaluation, here termed as ‘direct’, evaluates the losses by using only the mean values of the main variables involved (rate of events and frequency of the damage levels), thus providing an approximation of the expected losses. The second method, named ‘probabilistic’, takes into account the uncertainties related to the number of events (hazard) and the damage levels (vulnerability), thus determine the probability associated to each level of loss. Both methods express the risk as the economic losses to dwellings within a reference period of time. Two alternative hazard results are also used to show the influence on the calculated risk: the first one considering the seismicity uniformly distributed within seismic source zones; the second one clustering the strong seismicity in geographically narrowed source zones and scattering the low seismicity over large source zones.