GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 Vis maior, cui resisti non potest M. Stucchi 1 , G. Valensise 2 1 INGV, Bologna, Italy 2 INGV, Rome, Italy What do the Mw 5.8, 2002, San Giuliano di Puglia, the Mw 6.3, 2009, L'Aquila, and the Mw 6,0, 2016, Amatrice earthquakes have in common? First and foremost, they are the three most recent damaging and deadly earthquakes to have hit Italy. In addition to that, all three events caused the collapse of buildings that have been identified as "built with inexperience or fraud" by three independent Italian courts; these collapses killed the 100% of the 27 victims of the 2002 earthquake (all in one building), nearly 50% of the 309 victims of the 2009 earthquake (14 buildings), and an unknown fraction – probably over 50% – of the victims of the 2016 earthquake. These three moderate-size earthquakes tested the vulnerability of three unlucky Italian municipalities, showing the extreme variability in the response of their building stock and the extreme vulnerability of some buildings, and specifically of small- to mid-size reinforced concrete apartment complexes. Most importantly, the three earthquakes also share the attempt to consider them "exceptional" by the defendants – builders, contractors, and administrators – and by their lawyer teams: this presumed exceptionality eventually led to the total collapse of buildings that would otherwise have resisted ordinary earthquake ground shaking. In some specific trials (some of which are ongoing) this issue became a fundamental battle horse: such is the case of the collapse of two twin reinforced concrete buildings that were literally turned to dust following the 24 August 2016, Mw 6,0, Amatrice, Central Italy earthquake (Tribunale di Rieti, 2020). Therefore, much of the hearing was devoted to proving that the earthquake was indeed “exceptional” (ANSA, 2021; Stucchi, 2021). We maintain that from the scientific point of view no earthquake can be considered “exceptional”, for the very reason that no earthquake can be regarded as “regular” or “standard” (see discussion in Valensise et al., 2022). In fact, as the hearing progressed – albeit in a rather confused fashion – it became clear that the invoked exceptionality concerned only the ground shaking, not the earthquake per se. But, once again, what level of ground motion qualifies as “exceptional” from a purely scientific point of view? Indeed, the ground shaking recorded in Amatrice was rather strong, also thanks to the presence of recording instruments inside the town, not far from the collapsed buildings. But why expert engineers, forensic engineers and even seismologists, all of them active participants in the hearings as technical assistants to either the attorney or the defendants, did insist on proving that the ground shaking was “exceptional”? The answer is that all defendants, along with their lawyers, were invoking the force majeure concept: a legal principle that derives from Roman law (“vis maior cui resisti non potest”)