Sequence-based hazard analysis for Italy considering a grid seismic source model

Earthquakes are usually clustered in both time and space and, within each cluster, the event of highest magnitude is conventionally identified as the mainshock, while the foreshocks and the aftershocks are the events that occur before and after it, respectively. Mainshocks are the earthquakes considered in the classical formulation of the probabilistic seismic hazard analysis (PSHA), where the contribution of foreshocks and aftershocks is usually neglected. In fact, it has been shown that it is possible to rigorously, within the hypotheses of the model, account for the effect of mainshock-aftershocks sequences by means of the sequence-based PSHA (i.e., SPSHA). SPSHA extends the usability of the homogeneous Poisson process, adopted for mainshocks within PSHA, to also describe the occurrence of clusters maintaining the same input data of PSHA; i.e., the seismic rates derived by a declustered catalog. The aftershocks’ occurrences are accounted for by means of conditional non-homogeneous Poisson processes based on the modified Omori law. The seismic source model for Italy has been recently investigated, and the objective of the study herein presented is to include and evaluate the effect of aftershocks, by means of SPSHA, based on a new grid model. In the paper, the results of PSHA and SPSHA are compared, considering the spectral and return periods that are of typical interest for earthquake engineering. Finally, a comparison with the SPSHA map based on a well-established source model for Italy is also provided.