Digital Survey and Structural Investigation on the Triumphal Arch of Caracalla in the Archaeological Site of Volubilis in Morocco: Retracing the Timeline of Collapses Occurred during the 18th Century Earthquake

The Lisbon earthquake occurred in 1755, which affected Morocco seriously, provoked the collapse of the Triumphal arch of Caracalla in Volubilis. The currently visible monument is the result of the rebuilding carried out in 1930 by French restores. In this paper, the timeline of collapses caused by the subsequent seismic quakes is retraced aimed at estimating the lower bound of the intensity of the 18th century earthquake, based on structural investigations carried out on rigid-block and continuous FE models. The historical investigations and the digital survey carried out by the authors in 2017 served as the base of knowledge to drive the analyses. Results of the analyses of the two models are very comparable and provide that a low acceleration of 0.168 g was sufficient to provoke the collapse of the arch and explain the reason why the expected earthquake acceleration in the zone of the archaeological site of Volubilis provided by the current Moroccan seismic code is exactly 0.16 g. Therefore, with the purpose of assessing also the current seismic vulnerability of the arch, this result leads to state that the capacity is equal to the seismic demand, and, therefore, too low to ensure the safety in the case of un unexpected event.