Probabilistic seismic hazard analysis for seismic sequences

Earthquakes are typically clustered both in space and time. Seismic h azard , expressed in terms of rate of exceedance of a ground motion intensity measure , classically refers to ma i nshock s, which means that such a rate is computed filtering the rate o f occurrence of events of largest magnitude within each cluster of earthquakes. This kind of probabilistic seismic hazard analysis (PSHA) is used for structural design or assessment in t he long - term. R ecently, a similar probabilistic approach has been adopted to perform aftershock probabilistic seismic hazard analysis ( APSHA) , c onditional to mainshock occurrence. It is to be used for short - term risk management. PSHA often refers to a h omo geneous Poisson p rocess to describe event occurrence, while APSHA models aftershock occurrence via a non - homogeneous Poisson process , whose rate depend s on the magnitude of mainshock that has triggered the considered sequence . However, the whole cluster , c omprised of mainshock and aftershocks, occurs with the same rate of the mainshock , and this paper shows how it is possible to analytically co mbine results of PSHA and APSHA to get a probabilistic seismic hazard analysis for mainshock - aftershocks seismic se quences (SPSHA) . Results of the illustrative application presented help to assess the increase in seismi c hazard considering the probability of exceeding a n acceleration threshold (e.g., that considered for design) also considering aftershocks .