GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 and appears in many civil law systems and in common law doctrines. Application of this principle to the case of earthquakes appears inherently ill-posed, because antiseismic provisions and antiseismic design are expressely intended to protect buildings from strong earthquakes too. Conversely, the “vis maior” principle is described by the Dutch lawyer Anton Matthaeus (1601-1654) as a case where “insolitum de quo omnino cogitatum non est, quive timeri non potuit tempore locationis” (“an unusual thing which was not thought of at all, which could not be feared at the time of the agreement": Matthaeus, 1653). Clearly, an earthquake in the core of the Apennines could never qualify for “an unusual thing”, no matter how strong it was, and any attempt to prove it was indeed not only unusual but also exceptional, should be simply discounted. Nevertheless, the defendants/lawyers must have thought that it is worth trying, as proving the “vis maior” concept would have implied that the torn down building was not requested to stand, or was allowed to collapse; regardless of its (poor) design, of any confirmed discrepancies between the planned and the actual construction, and of its state of repair when the earthquake struck. In other words, the collapse of a building under “vis maior” could not be taken as a surprise. The defendants’ lawyers suggested that the exceptionality was certified if the recorded ground accelerations exceeded the design shaking levels prescribed by the current building code; this stance implicitly assumes that the codes according to which the buildings were originally designed were not more severe than the current code, and does not take into account that such comparisons are inherently slippery (Iervolino. 2013). Indeed, the ground shaking (PGA, SA, etc.) recorded at Amatrice did overcome the current building code thresholds for a 10% exceedance probability in 50 years, by as much as three times. Notwithstanding, the issue of the exceedance of the design spectra by the recorded ground shaking is discussed in many papers (see for instance Iervolino et al., 2018, 2019), and does not automatically imply that either the seismic hazard model or the building code are “wrong”. Any reader willing to read the nearly 500 pages comprising the “Motivazioni della sentenza” (explanation of the verdict) will likely be astonished by the quantity and quality of the scientific and technical questions discussed in the text, and will inevitably wonder how the judges managed to navigate through them. The impression is that any trial where “vis maior” has been invoked will end up in an expensive and time-consuming autopsy of the collapsed buildings; a procedure whose cost could have been spent before the earthquake in favor of the inhabitants’ safety. At any rate, justice will make its course. Contrary to science, in a court sooner or later the discussion stops, and the judge decides what is right and what is wrong. But, from the scientific point of view, the above-mentioned questions raise a further major issue: is it correct to conclude that a building subject to ground shaking larger than the building code prescription is “allowed to collapse”? And if it does not, is it just a matter of chance, or luck? The question is crucial, not only for the safety of buildings and of their inhabitants, but also to inform those scientists who maintain that the accelerations implied by the current hazard estimates are systematically too low, and therefore may cause further collapses and victims. In some cases it is evident that while the goal of