GNGTS 2013 - Atti del 32° Convegno Nazionale

In the last seismic sequence (blue in Fig. 2) strong seismic activity started around 1850, with a first period (1850-1872) in the Hellenides, which was soon followed by another crisis in the same zone in the last part of the XIX century. As in previous cases, these crises were accompanied by major earthquakes in Calabria (1905 M=6.9, 1908 M=7.2). Subsequently, seismic phases underwent a progressive northward migration through the periAdriatic zones, up to reach the Central Dinarides and Central-Northern Apennines. Insights into the possible future seismic behaviour of the Italian zones here considered may tentatively be inferred from the seismicity patterns given in Fig. 3, which show the distribution of major shocks in the presumed seismic sequences identified in Fig. 2. It is possible to note that in the two presumably complete sequences, green and yellow in Fig. 2, major earthquakes have occurred in most periAdriatic zones (Figs. 3a,b). This could indicate that the development of a northward step of the whole Adria plate requires the activation of most decoupling boundary sectors. Tentatively assuming that such tendency is systematic over time, one might use the distribution of major periAdriatic earthquakes in the last seismic migration pattern (Fig. 3c) to recognize which Italian zones have not yet undergone a significant decoupling and are thus most prone to next strong shocks. For instance, in Fig. 3c it can be noted that the Northern Dinarides and the northernmost Apennines have so far experienced a level of seismicity much lower than the one they underwent in the previous sequences (Fig. 3a,b). This observation may also partially be applied to the Southern Eastern Alps, where only one strong seismic crisis has so far occurred (Friuli 1976, M=6.5, 5.6, 5.9, 6.0). Thus, one could suppose that in the next future the occurrence of major earthquakes in the Northern Apennines and perhaps in the Alps is more probable than Fig. 3 – Distribution of major earthquakes that oc- curred in the periAdriatic zones here considered during the green, yellow, and blue seismic se- quences pointed out in Fig. 2. 98 GNGTS 2013 S essione 2.1