Two unknown M>6 historical earthquakes revealed by palaeoseismological and archival researches in eastern Calabria (southern Italy).: Seismotectonic implications

The seismicity of Calabria is among the strongest in the whole of the Mediterranean, but is now well known on its Ionian side. Palaeoseismological investigations in eastern Calabria and archival research have tried to shed light on earthquake recurrence and seismogenetic source geometry. Trench investigation across the Lakes fault (Sila massif) shows this fault to be definitively responsible for the Mw = 6.7, 1638 earthquake, and provides a well-constrained age range for its penultimate event (early 7th century AD). On the other hand, after research in local and national archives, another previously unknown relevant historical earthquake has been discovered (1744, Mw = 6.2), which struck an area conterminous to the SE tip of the Lakes fault. We hypothesize a NW-SE active Sila fault system that accommodates regional similar to N-S extension through normal-to-sinistral segments, each one capable of generating earthquakes with magnitude in the range of 6.2-6.7. Since 1638, this system ruptured almost entirely from NW towards SE (1638-1744-1832), with the exception of the northwestern segment, the 'silent' Cecita fault.