GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 mainly based on news collected through macroseismic postcards, or on material gathered from the Observatories, newspapers, and local correspondence; the most important of these is certainly the Bollettino Mensuale, published by the Central Observatory of the Real Collegio Carlo Alberto in Moncalieri. Intensity estimates and descriptive sheets The testimonies collected helped to expand and improve the knowledge available on these events and to detail the locations affected and the effects observed. The main objectives of the work are the preparation of descriptive sheets and the assignment of a macroseismic intensity value, i.e. the classification of the effects documented at each location based on the information collected, using the Mercalli-Cancani-Sieberg macroseismic scale (MCS, 1930), also adopted by the National Seismic Catalogue (CPTI15). The estimation of intensity is a very delicate operation, made even more difficult by the fact that, since we are dealing with minor events, the information background is limited overall. The information available is sometimes not sufficient to define a precise effects scenario, so the uncertainties are quite high. All the information found was then organized according to a common reference scheme. The result is a descriptive sheet, for each earthquake, outlining the research path carried out, starting from the verification of preliminary studies up to an ex novo search of all available sources (whose complete references are given in the bibliography). In addition to the original CPTI15 record and the parameters assigned in the various parametric catalogues, all the possible problems found in the data, information on the sequence, on casualties or environmental effects, and the list of affected georeferenced localities with the estimated intensity for each parameterizable tremor are briefly reported in a format consistent with that of the macroseismic database linked to CPTI15 (DBMI15) (Locati et al., 2022). To complete the sheet, transcriptions of the texts of all the sources identified are then provided. Conclusions Although the evidence found in newspaper reports and in the archival record is sometimes rather limited, the work done has increased the knowledge available for each of the earthquakes considered, supplementing the available information and improving the estimates of intensity (Ix) of earthquake effects at the various locations. Comparing the 'new' data with those reported in CPTI15 (Tab. 1), it is evident that there has been a general re-evaluation of the value of Ix by at least half a degree and an increase in the number of localities where damage effects were recorded, calculated solely with reference to the main shock of each event. Overall, there is also a decrease in the number of cases where there is uncertainty between two degrees of the MCS scale in the maximum intensity estimates, from 4 cases with uncertainty to 1, out of the 6 earthquakes reviewed. Another considerable result of this research is the identification and parameterization of two other earthquakes close to the damage threshold. These are the events of 29 March 1887 at 08:58 GMT (although there are still some uncertainties