Updates on a possible statistical approach to the identification of preparatory phases of earthquakes

Our research represents a first attempt to answer a question of crucial importance in short-term seismic hazard: can we identify preparatory patterns in seismic events preceding a large event from an isolated cluster of small earthquakes? If not basing on physics, at least on statistics of previous occurrences? Fortunately, only a scant percentage of clusters ultimately triggers a damaging mainshock; in any case, can we provide reliable information about such a possibility? Here, we perform a retrospective analysis of the structural, physical and statistical features of clusters of non-precursory seismicity and “foreshocks” until the occurrence of their respective mainshock in Italy (and other regions) during the last decades. We highlight some characteristics that come out to be more likely associated with impending large-scale destabilization of crustal volumes. We also compare our results on real seismic catalogues with ETAS-simulated ones. Moreover, we suggest possible explanations for our observations considering slow destabilization processes at work in the brittle crust. Our effort would like to be a first, preliminary attempt towards the possibility of assessing the probability that an ongoing seismic cluster is likely to flow into a large earthquake. Then, we also apply our results to recent or even still ongoing clusters.