The Calabrian seismicity during the Viceroyalty of Naples: sources silence or silent sources? The case of the strong 1744 earthquake

In the Italian seismic catalogues, Calabria is characterized by an earthquakes time-distribution confined almost exclusively between the catastrophic events of 1638 and 1905-1908. The outward absence of seismicity before the first half of the 17th century could be related to a dormancy of the seismogenetic sources or to the silence or loss of historical contemporary sources. With the aim of casting light on this issue, we performed research archive for the period 1500-1750. The investigation was addressed towards recent and coeval Calabrian historiographical works and local chronicles, but above all toward �unusual� 16th-19th century manuscripts, such as notarial deeds, Relationes ad Limina and sheets of Avvisi. Thanks to the discovery of hundreds of inedited news, we pinpointed an unknown earthquake (Mw=6.2) that struck central-eastern Calabria on March 21, 1744; besides, new parameters for other, four, strong events (1609, 1624, 1640, 1743), which were poorly-characterized or absent in previous seismic compilations were provided. These results put in evidence the existence of a �subterranean� strong seismicity that occurred in modern times (i.e., in the period of catalogue completeness) that still awaits to be discovered in archives and libraries. Finally, the highest-intensity datapoint distribution suggests some hypotheses on the geometry and location of the seismogenic sources of the region.