Abstract
The Italian earthquake catalogue is considered to be fairly complete starting from the 17th century and for classes of earthquakes of magnitude greater than 5.5. However, dedicated historical research has highlighted the fact that even in areas believed to be well-recognised from the seismological standpoint, authoritative traces of local earthquakes that have caused damage may also emerge. In this study, we present the results of a pilot study performed for the Upper Valtiberina within the framework of the INGV research programmes in the years 1999-2001, expanded and revised in 2005. The study highlighted seven local medium intensity earthquakes, which nonetheless caused damage to buildings. Besides the results, which as a whole have allowed us to classify 18 effects in 6 sites, the research method adopted is also presented. It is a method applicable to other cases as well, where the chronological earthquake indicators are unknown, being capable of unearthing earthquakes unknown to the tradition of seismological studies and the catalogues in use. A selection of the manuscript sources used is presented in the Appendix.
Highlights
The territory of Upper Valtiberina, formed by the first stretch of the River Tiber, about 60 km in length, is situated on the border between Eastern Tuscany and Northern Umbria, and is one of the most important seismic areas in the whole of the Central Apennines
Sansepolcro was the main centre of the Upper Valtiberina, with over 5000 inhabitants (5041 in 1551), mostly engaged in agriculture and the wool and silk trade
At the Municipal Historical Archives of Sansepolcro, within the series II (Riforme, provvisioni e deliberazioni dei consigli, reg. 14), we have found a long memorial on this earthquake written by the chancellor of the community on 27th February 1558, bearing witness to the damage in Sansepolcro and Città di Castello
Summary
The territory of Upper Valtiberina, formed by the first stretch of the River Tiber, about 60 km in length, is situated on the border between Eastern Tuscany and Northern Umbria, and is one of the most important seismic areas in the whole of the Central Apennines. As regards the two main urban centres of the area under examination here, Sansepolcro and Città di Castello, it should be remembered that in the past they had both suffered damage effects equal to the IX degree on the MCS scale. In Città di Castello the maximum destructive effects were caused by the earthquake on 30th September 1789: for both of these, see Castelli et al (1997) and Boschi et al (2000); in particular for the 1789 earthquake Castelli (2002) has elaborated a very accurate effects scenario for the urban area. The aim of this study is not to make a new evaluation of the seismic hazard of these two historical towns, but to identify the unknown earthquakes in the area being examined and to make. Me =equivalent magnitude, according to Gasperini and Ferrari (2000); Mw=moment magnitude, according to CPTI Working Group (2004)
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