Filling gaps in historical earthquake archive by geo-archaeological methods: a case history from Italy

Abstract All over the world, archaeological sites, which have alternated destruction and reconstruction following strong earthquakes can disclose important historical / seismological data. Particularly instructive is the case of St. Angel cave in Palombaro (Abruzzo Region, Italy). Combining the geological, archaeological, archaeometrical and chronachistic study, we constrained the seismic history of the last 1000 years of a large area of central Apennines of Italy, and therefore results are of wide interest. This place reveals various phases of worship, confirming itself as a place of religious importance bridging the gap between paganism and Christianity. The lithostratigraphy of the area made possible to practice water-worship, as deduced by a system of tubs present in the cave. The interpretation of the cult refers to chthonian divinities in charge of thaumaturgic properties symbolically linked to endogenous geologic phenomena. A rupestrian church from the 10th-11th -century was built and reported in a 1064 CE chronicle as dedicated to St. Michael Archangel. Two vast collapses of the church, have been documented by the archaeological stratigraphy, dating of the archaeological finds, layering of the church walls, and changes in style and building materials. Geoarchaeological data, combined with the chronicles, suggests that the first collapse should be attributed to the 1209 CE earthquake (Mw >>6, I HD). Therefore, the failure of the Church of St. Angel would represent the first evaluated point of the seismic damage extension, assessable to the IX MCS intensity. A more recent collapse is attributed to the 1706 CE earthquake (Mw 6.8, I XI MCS). Finally, the remains of the church were seriously damaged and spoiled after the 1933 earthquake (Mw 5.9, I IX MCS) and then poorly restored.