EVALUATION OF A SEISMIC QUIESCENCE PATTERN IN SOUTHEASTERN SICILY

Southeastern Sicily experienced a very peculiar seismic activity in historic times, with a long series of ruinous earthquakes. A vast large event, with magnitude probably in excess of 7. 5, occurred on Jan. 11, 1693, totally destroying the city of Catania and killing 60,000 people. Only a few moderate events were reported since then, and a seismic gap issue has been proposed on this basis. A close scrutiny of the available data further shows that all significant seismic activity ceased after year 1850, suggesting one of the largest quiescence patterns ever encountered. This is examined together with the complex tectonic setting of the region, characterized by a wrenching mechanism with most significant seismicity located in its northern graben structure. Within the limits of reliability of present semi-empirical approaches it is concluded that the available evidence is consistent with the occurrence of a moderate-to-large (m approximately equals 6. 0) event in the near future.