Palaeoseismic evidence of a mainshock in the Lamezia Terme area during the March 1638 seismic sequence (MW ~7, Calabria, southern Italy)

Among the devastating earthquakes to have struck the Italian peninsula are those of the March-June 1638 sequence in central Calabria, which caused over 10,000 deaths and an unprecedented level of destruction spanning from the Tyrrhenian to the Ionian seas. Currently, Italian seismic catalogues report the macroseismic epicentres of two mainshocks: one on 27 March located on the south-western slopes of the Sila plateau (MW 7.1), and another on 8 June on the eastern side of the Sila (MW 6.8). However, neither of these epicentres fully explains the complex distribution of the highest intensities. Palaeoseismological studies conducted in the 2000s identified the source of the June earthquake in the inner Sila plateau (Lakes Fault). Meanwhile, historical investigations suggested that two mainshocks occurred in March: one on Saturday 27, between the upper Crati and Savuto river valleys, and another on Sunday 28, in the western Catanzaro Strait. New palaeoseismological evidence, together with indications of active tectonics, supports the hypothesis that the mainshock on 28 March was generated by the rupture of the northern border fault of the Sant’Eufemia plain (Sant’Eufemia Fault). This normal fault likely extends westwards well beyond the Tyrrhenian coastline into the Gulf of Sant’Eufemia, with a WSW–ENE trend.