Medium-term precursors of strong earthquakes in southern Italy

Abstract

During the last two centuries, the most intense earthquakes ( M ≥ 6) in southern Italy have regularly occurred some years (less than 5) after the main activations of the southern Dinarides-Albania seismic zone. To explain this interrelation, we advance the hypothesis that the strong decoupling earthquakes at the Adriatic-Dinarides collisional border cause a perturbation of the strain and stress fields which propagates through the Adriatic plate with rates of some hundreds of km per year. When this migrating perturbation reaches the opposite border of the Adriatic plate it may induce seismic dislocations in the highly fractured southern Apennines and Calabrian arc. Statistical tests have been carried out to estimate the reliability of possible Balkan seismic precursors of Italian earthquakes. The best results have been obtained with a precursor represented by the occurrence of at least one earthquake with M ≥ 6.5 or at least two shocks with M ≥ 6.0, assuming an alarm time of five years. In this case, the probabilities of a successful prediction (i.e. the occurrence of an event with M ≥ 6.0 in southern Italy within five years from the Balkan precursor) and of a non-alarm are 83% and 10%, respectively, and the probability of obtaining these results by chance is very low, less than 0.1%.