GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.2 GNGTS 2024 Statstcal analysis of the seismicity of the last 30 years at Mt. Somma-Vesuvius G. Dalla Via 1 , P. Ricciolino 1 , D. Lo Bascio 1 , A. Tramelli 1 1 Isttuto Nazionale di Geofsica e Vulcanologia, Sezione di Napoli, Osservatorio Vesuviano, Napoli, Italy The last erupton of Mt. Somma-Vesuvius occurred in 1944, and since then has been quiescent showing only fumarole actvity and moderate seismicity. The Md=3.6 event recorded on 09/10/1999 is the strongest record in the last 30 years. Here we present an updated statstcal analysis of the seismicity by analysing the three main seismic catalogues constantly flled in by INGV – Osservatorio Vesuviano: ● The catalogue of detected events at staton OVO which starts in 1972 and counts 11783 earthquakes with duraton magnitudes ranging from -1.5 to 3.6. ● The catalogue of detected events at staton BKE which starts in 1998 and counts 20196 events. ● The catalogue of located events which starts in 1998 and counts 8558 events. Magnitudes of events in this and BKE catalogues range from -2.5 to 3.6. The completeness magnitude computed for the OVO catalogue is Mc=1.9 and the b-value ranges between 1.0 and 2.5. The higher values correspond to the period 1980-1985, successively the b- value decreased to about 1.0 untl the early 2000’s. More recently, the b-value for the OVO catalogue slowly but steadily increased again to about 2.0 (~2014-2016), decreasing to 1.8 at present tme. The annual occurrence rate is currently much lower than before 2000 (with a maximum of almost 700 events/year in 1999 when the Md=3.6 was recorded) and is generally lower than 100 events/year. The analysis of the BKE catalogue gives an overall completeness magnitude of Mc=0.5 and a b- value in the range 0.8-1.2 in recent years. The annual seismicity rate, which reached values of 2000 events/year during 1999, decreased to less than 500 events/year in 2004. In successive years, seismicity grew up to about 750 and 1000 events/year in the period 2007-2010 and 2018-2022, respectvely. However, the Gutenberg-Richter distributon shows a knee around Md=2.1. Our analysis, in agreement with previous results (D’Auria et al., 2013), suggests that at least two populatons of earthquakes coexist in the BKE catalogue. This characteristc is mainly visible in the data before 2015, whereas it does not show up in more recent records. The two populatons were analysed separately and gave values close to b=1 and b=1.7. The main characteristc of the catalogue of located events is a signifcant variaton in completeness magnitude with tme, with completeness magnitude abruptly lowering during 2015 from about