GNGTS 2013 - Atti del 32° Convegno Nazionale

recognized in Calabria (e.g, Tansi et al. , 2007). The above interpretation is also consistent with the quantification of the effects of post-seismic relaxation induced by strong earthquakes in the Hellenic sector (Mantovani et al. , 2012a), which shows that such phenomenon may have influenced the Calabrian shocks that occurred some years later. A more detailed information on the time correspondence between major earthquakes in the Hellenides and Calabria is provided by Tab. 1, which reports the Calabrian events with M≥6.0 and the ones of the Hellenic zone with M≥6.5, that have occurred since 1600 A.D. Tab. 1 – Larger earthquakes in Calabria and Hellenides. Calabria (M) Hellenides (M) 1626 (6.0) 1625 (6.5) 1638 (7.0, 6.9) 1630 (6.5) 1636 (7.2) 1659 (6.6) 1658 (6.7) 1701 (6.6) 1732 (6.6) 1743 (6.9) 1767 (6.0) 1766 (6.6) 1767 (6.7) 1769 (6.8) 1783 (7.0, 6.6, 7.0) 1773 (6.5) 1791 (6.0) 1783 (6.5, 6.6), 1786 (6.5) 1820 (6.6) 1832 (6.6) 1825 (6.7) 1836 (6.2) 1833 (6.5) 1854 (6.2) 1851 (6.8) 1870 (6.1) 1866 (6.6), 1867 (7.2), 1869 (6.7) 1894 (6.1) 1893 (6.6) 1905 (7.0), 1908 (7.1) 1895 (6.5), 1897 (6.6) 1948 (6.5, 6.5) 1953 (7.0, 6.6) 1983 (6.7) In the above list it is possible to see that all Calabrian shocks were preceded, within 10 years, by at least one event in the Hellenic zone. This evidence may suggest that a Calabrian earthquake may hardly occur not being preceded by significant seismic activity in the Hellenides. On the other hand, one can note that only 12, out of 20 Hellenic crises, were followed within 10 years, by at least one Calabrian earthquake, which indicates that the role of Hellenic shocks as precursors of Calabrian events may be affected by uncertainty. In particular, it is worth noting that since 1948 no Hellenic events have been followed by an event in Calabria. The drastic increase of false alarms in that period is clearly related with the fact that since 1947 no earthquakes with M≥5.5 have occurred in Calabria. Such long quiescence (66 years) is rather anomalous with respect to the previous seismic behaviour of Calabria, considering that from 1626 to 1947 the average inter-event time between M≥5.5 shocks was of 12 years, and that it was never longer than 41 years. In order to find a possible explanation for such a long quiescence and for the fact that since the half of the XX century the correspondence 100 GNGTS 2013 S essione 2.1