The forgotten vulnerability: A geology- and history-based approach for ranking the seismic risk of earthquake-prone communities of the Italian Apennines

Abstract

The 2016–2017 Central Italy earthquakes have shown that the local seismic risk is dominated by the extreme vulnerability of the building stock. We attempt to rank the vulnerability of Apennines' settlements based on a combined geological-historical approach. We first discuss the reasons of the apparent paradox caused by the very different seismic response of Amatrice and Norcia, both strongly hit by the 24 August 2016 earthquake (Mw 6.0). Based on the awareness that strong earthquakes force building reconstructions and changes in the individual and societal perception of seismic risk, we assume that the global vulnerability of Italian settlements increases with time since the last significant earthquake. We focus on the very active seismogenic areas straddling Italy's Apennines. We then use data on the local seismogenic sources and earthquake history to (1) select the municipalities that are more likely to suffer from destructive ground shaking, and (2) rank them as a function of the time elapsed since the latest earthquake, i.e. in terms of increasing vulnerability. We hence identified 716 municipalities, totaling about 5% of the Italian population, over 50% of which have not experienced destructive shaking since 1861, when the Kingdom of Italy reunited a number of smaller states. As such they are primary candidates to a poor performance in future significant earthquakes (Mw > 5.5) and should be given priority in any statewide vulnerability reduction plan. All results and elaborations, including the seismic histories of each of the selected localities, are also supplied in a specifically designed web-GIS.