Early results of a systematic revision of Ferrarese seismicity of the 13th-15th centuries

Abstract

Within the PRIN 2020 project NASHA4SHA [Fault segmentation and seismotectonics of active thrust systems: the Northern Apennines and Southern Alps laboratories for new Seismic Hazard Assessments in northern Italy] and in order to improve our general knowledge of the seismic record of the Ferrara area, we are proceeding to examine the ancient local narrative sources, not only to find information on “unknown” or “forgotten" earthquakes, but primarily to improve the understanding of earthquakes already known through a comprehensive study of the original texts which are relied on by the reference studies of the CPTI15 catalogue (Rovida et al., 2022). Far from limiting ourselves to searching for “earthquake news” and taking them out of context, as we tended to do in the "heroic" days at the dawn of modern historical seismology, we attempted here a more ambitious undertaking. Our aim is to examine original earthquake news in their cultural framework, to check their intrinsic quality and "authoritativeness", and thus to improve the quality of general knowledge on historical earthquake observations. Using data extrapolated from narrative written sources (such as chronicles and annals) to compile earthquake catalogues sometimes risks isolating the data themselves and undermining their evaluation. Indeed, news taken out of the context that reports them, while useful in itself, remain impoverished, like archaeological findings whose site, location and circumstances of discovery are unknown. Up to now our study has considered some dozen earthquakes with M ≥3.5, dated between 1234 and 1495, of which 11 are located by the CPTI15 catalogue (Rovida et al., 2022) in Ferrara, 3 in Modena, while a couple of cases are unknown to the CPTI15 catalogue. A couple of these earthquakes were never studied at all, in several cases epicentral parameters are derived from reference studies that are almost 20 years old, and in 5 cases even 40 years old. The informative basis for these earthquakes, as summarized in Locati et al. (2022) and Rovida et al. (2022) is rather poor. In many case information on a single locality is available from a single source, whose intrinsic value and reliability are also questionable. The preliminary results of the revision work are generally an improvement of the intensity estimates. In a few cases, the studied earthquakes turned out to be doubtful or completely fake