GNGTS 2013 - Atti del 32° Convegno Nazionale

in Calabria and Southern Apennines. A intermediate probability of major events, lower than the one in the northern Apennines and higher than the one in southern Italy, may tentatively be associated to the Central Apennines. The uncertainty that affect this hypothesis is due to the fact that during the present sequence (Fig. 2) such zone has been affected by a number of moderate shocks (1933, 1943, 1950 and 2009), so it cannot be excluded that some further release of seismic energy could occur. The proposed prediction in the zones of the Italian peninsula is suggested by the distribution of seismicity in the most reliable and complete part of the seismic history. However, one must take into account that such period only involves a limited number of seismic sequences (Fig. 2), which may imply uncertainty on the hypothesis that proposed seismotectonic mechanism is stationary in time. Anyway, the hypothesis that the probability of major earthquakes is higher in central-northern Italy than in the southern part of the Italian peninsula is also suggested by the implications of two systematic interactions of periAdriatic seismic zones. The first interrelation has been recognized between the Southern Apennines and the Southern Dinarides (e.g., Viti et al. , 2003; Mantovani et al. , 2010, 2012a). The possibility that major earthquakes in the first zone may influence the probability of major shocks in the second has been suggested by the fact that the strong shock (M = 7.0) that occurred in the Montenegro zone on April 1979 was followed on November 1980 by a major event (M = 6.9) in the Irpinia zone of Southern Apennines. This first suspect has been then reinforced by the present knowledge about the tectonic context in the southern Adriatic region and surrounding belts. In particular, the fact that the occurrence of seismic slip at the thrusting fault located beneath the Southern Dinarides, as the one that developed with the 1979 Montenegro event (estimated of 1-2 metres, e.g., Benetatos and Kiratzi, 2006), implies a roughly East to NE ward motion of the Adriatic lithosphere, which causes the reduction of the vertical flexure of that domain and, consequently, may favour the activation of the belt parallel normal faults recognized in the Southern Apennines. The presumed interaction is also compatible with the quantification of the strain perturbation that was presumably induced in the Irpinia zone by the 1980 Montenegro event (Viti et al. , 2003; Mantovani et al. , 2010, 2012a), which indicates that the post-seismic strain rate induced by the Montenegro earthquake is expected to reach its maximum amplitude in the Southern Apennines about 1-2 years after the triggering event, i.e. a time delay which roughly corresponds to the interval that elapsed between the April 1979 Montenegro and November 1980 Southern Apennines shocks. The possible relationship between stress/strain rate increase and triggering of seismic activity is pointed out in several works (e.g., Pollitz et al. , 1998; Viti et al. , 2003, 2013). The possibility that the interaction of Dinaric and Apennine seismic sources is a systematic phenomenon is suggested by the comparison of the seismicity patterns of the two zones considered (Viti et al. , 2003; Mantovani et al. , 2012a), which reveals that in the last two centuries all strong shocks in the Southern Apennines (M>5.5) were preceded within few years (less than 5) by one or more strong earthquakes in the Southern Dinarides (M≥6). Since the probability of having such a regular correspondence merely by chance is very small (Mantovani et al. , 2012a), it is plausible to suppose that such interrelation may have a deterministic explanation, based on the tectonic mechanism described above. The fact that this significant time correlation can be recognized for the most recent, complete and reliable part of the seismic catalogue (1820- 2013) implies that this phenomenon might provide a tool for recognizing the periods when the probability of strong shocks in Southern Apennines is highest. Another systematic seismic interrelation has been recognized between themajor earthquakes of Calabria and those of the Albania-Cephalonia Hellenic sector, where the collision between the Adria plate and the Aegean-Balkan system takes place (Mantovani et al. , 2009, 2013b). The tectonic mechanism presumably responsible for this phenomenon is similar the one described for the previous case. In particular, the fact that a seismic activation of the Hellenic thrust zone increases the probability of seismic slip at the normal and shear faults which are 99 GNGTS 2013 S essione 2.1