GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Insights on the seismotectonics of the Alps- Apennines transiton zone, NW Italy, afer the 2022 earthquake sequence near Genoa E. Eva 1 , M.G. Malusà 2 and S. Solarino 1 1 Isttuto Nazionale di Geofsica e Vulcanologia, Osservatorio Nazionale Terremot, Genoa, Italy 2 Department of Earth and Environmental Sciences, University of Milano-Bicocca, Milan, Italy In the years 2021-2022 three seismic sequences located respectvely close to Savignone (August - October 2021), Borzonasca (February – March 2022) and Bargagli (September – October 2022) struck the area ENE of Genoa, in the region classically referred to as the transiton between the Alps and the Apennines. According to the instrumental catalogues, seismic events in this sector are infrequent and of low magnitude and even the catalogues of historical seismicity do not report major seismic events. Nevertheless, the earthquake of September 22, 2022 in the Bargagli area (red star in Fig.1), reached a magnitude M w 4.0. It was felt in a large area and caused minor damages to a cemetery and a church in Bargagli and in a nearby village, respectvely. Given the low number of seismic events occurred in the area in the past, the three seismic sequences represent a valuable dataset to shade some light on how the convergence between Africa and Europe is presently accommodated across the Alps-Apennines transiton zone. They are thus the topic of this study. It must be remarked that according to the catalogue CPTI15, only few earthquakes with a magnitude comparable with the event in Bargagli have occurred near Genoa but none in the area of the 2022 earthquake. The frst step of this study consisted then in a reappraisal of the events of the last century with an approach proftng from the instrumental data for the events of the last century stored at the Sismos database. In partcular, historical seismograms and seismic bulletns provided a new locaton for the September 21, 1924 earthquake originally located ofshore about fve kilometres from the Ligurian coast (green star in Fig.1). Based on the results obtained, this earthquake locates near Bargagli (blue star in Fig. 1) and deserves atenton in that it can provide insights on the relatonship between recent and historical seismicity (Solarino and Eva, 2023). Although the new locaton has no partcular implicatons for the seismic hazard of the area, however it represents an important informaton to be taken into account in the calculaton of the return period.