The March 1952 seismic sequence at Mt. Etna volcano (Italy): from the historical reappraisal to the seismotectonic implications for the S. Tecla fault

Mt. Etna exhibits a frequent seismic activity, often in the form of sequences and even with destructive events. These volcano-tectonic earthquakes, rarely exceeding M5, determine a high level of hazard. Here, we revised the 1952 seismic sequence, that started on 1–2 March with two damaging foreshocks and followed on 19 March by a strong mainshock. Our historical investigation allowed collecting a wide spectrum of contemporaneous sources, which were analyzed by classifying day-by-day information, as in an a-posteriori macroseismic survey, to follow the progression of damage effects during the sequence. Archive documents, photographs and contemporary footage were used to classify buildings according to the EMS vulnerability classes and to derive the percentages of damaged buildings. From a macroseismic viewpoint, the analysis allowed us to reconstruct the evolution of the seismic sequence in detail: cumulative effects of damage are evident only for the two stronger foreshocks, whereas new collected damage observations for the mainshock were worse than reported in the literature, with the destruction of the village of Linera and nearby localities, and a ‘human cost’ of two victims, sixty injured and 2,000 homeless people. As a result, now the epicentral intensity of the 19 March mainshock increases up to degree VIII-IX EMS (from VII-VIII), and the corresponding equivalent magnitude up to M_L 4.9 (from 4.4), this determining significant changes in the earthquake parameters. Outcomes also have implications for the seismic hazard assessment at the scale of the causative Santa Tecla fault, better constraining its seismotectonic behaviour and seismic potential.