GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 The crucial assessment of possible significant vertical movements preceding the 1908 Messina Straits earthquake N. A. Pino The 28 December 1908 Messina Straits earthquake is among the worst seismic catastrophes in human history and certainly the most catastrophic event ever in Europe. The ground shaking and the tsunami following the earthquake destroyed almost completely the areas of Messina and Reggio Calabria. The most likely death toll has been assessed as between 60 000 and more than 100 000, and at that time the population in the two towns were respectively of ∼ 140 000 and ∼ 45 000. Numerous geophysical studies focused on the possible seismic source and many geophysical investigations probing the crust in the straits have been accomplished in the last decades, but, despite periodical triumphant announcements, no convincing seismogenic fault has been detected by geophysical analyses (Argnani, 2022, and references therein) and an unequivocal identification of the causative fault is still missing. The scientific literature of the 100 years following the earthquake contains numerous studies proposing a variety of fault models, with the better constrained ones characterized by some differences in the geometry of the fault plane, but sharing a few key elements, such as approximately N-S orientation, with eastward, low-angle dipping, and peak dislocation located in the middle of the straits (see Pino et al., 2009, for a review). Nonetheless, in the last few years several other distinct solutions have been proposed – sometimes by the same authors – characterized by very different locations and geometry. These models would have critical repercussions in the prediction of the seismic ground motion in the Messina Straits area, where more than 700 000 people live today (Messina and Reggio Calabria total more than 400 000). These latter studies are based on specific hypotheses and/or arbitrary assumptions, on either the reliability of the coseismic geophysical measurements or the tectonic processes the data refer to, strongly affecting the conclusions of the analysis. Among these assumptions, the possibility of significant pre seismic (aseismic) subsidence has been also considered. If true, this circumstance would crucially affect the analysis of the original ground levelling measurements and, in turn, the resulting fault model, impacting considerably on the seismic hazard evaluation. Here, I critically review the available tide gauge data (Fig. 1), in order to