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

Abstract

Earthquakes are usually clustered in both time and space and, within each cluster, the event ofhighest magnitude is conventionally identified as the mainshock, while the foreshocks and theaftershocks are the events that occur before and after it, respectively. Mainshocks are theearthquakes considered in the classical formulation of the probabilistic seismic hazard analysis(PSHA), where the contribution of foreshocks and aftershocks is usually neglected. In fact, ithas been shown that it is possible to rigorously, within the hypotheses of the model, account forthe 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 formainshocks within PSHA, to also describe the occurrence of clusters maintaining the same inputdata 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 processesbased on the modified Omori law. The seismic source model for Italy has been recentlyinvestigated, and the objective of the study herein presented is to include and evaluate the effectof aftershocks, by means of SPSHA, based on a new grid model. In the paper, the results of PSHAand SPSHA are compared, considering the spectral and return periods that are of typical interestfor earthquake engineering. Finally, a comparison with the SPSHA map based on a well-established source model for Italy is also provided.