Reappraisal of a XVI century earthquake combining historical, geological and instrumental information

Abstract

The earthquake occurred during 1561 in Southern Italy heavily struck a zone known as Vallo di Diano. This is the only destructive earthquake whose epicentre is attributed to that valley. Two problems arise about this epicentral location: 1)the distribution of reported effect is highly asymmetrical, possibly reflecting population distribution at that time, 2)some geologist maintain that there is no evidence for ongoing active tectonics in the Vallo di Diano area. The basic question behind our work is the following: Is it possible that both expert judgement and computer techniques have up to now placed the 1561 epicentre in the wrong place, driven by asymmetrical distribution of observations and by site effects enhancing damage in the alluvial valley? It was possible to demonstrate that, when site amplification are taken into account, the location of an historical earthquake can vary significantly. This applies not only to epicentre but especially to extended seismogenic faults connected to large events. From the seismogenic point of view, we demonstrate that the location of the 1561 in the Melandro valley is more statistically significant than the one up to know proposed. More detailed geological data are however needed to lend support to the Val Melandro fault hypothesis.