GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.2 GNGTS 2024 b value tomography at Campi Flegrei : enlightening diferent rheological behaviour in volcanic areas A. Tramelli 1 , V. Convertto 2 and C. Godano 1.2 1 INGV-Osservatorio Vesuviano, Napoli, Italy 2 Department of Mathematcs and Physics, Università della Campania "Luigi Vanvitelli", Caserta, Italy. The b-value represents the relatve proporton of large and small events in the Gutemberg-Riechter relaton: log( N )= a-bM where N is the cumulatve number of earthquakes with magnitude larger than M and a and b are constant that characterize the seismic catalogue and, consequently, the area where the catalogue is flled in. The b value is, generally, close to 1 in tectonic areas. Its value increases with the medium heterogeneity and temperature and it decreases with increasing stress. We used the seismicity recorded in Campi Flegrei since 2005 to perform a tomography of the b value. This tomography revealed values that ranges between 0.7 and 1.8. A very good correlaton with the structure of the hydro-thermal system at the basis of the bradiseismic phenomenon is evidenced. The lowest values characterize the caldera at depth of 2-4 km. The highest values characterize the shallower structures below Pisciarelli and Solfatara. More precisely we observe the smallest b values where we expect the higher stress concentraton and for deepest seismicity. Conversely the highest b values are observed where the presence of a porous medium allows the passage of the volcanic gases. Values of b more close to typical tectonic ones are observed where the presence of faultng structure is documented. Corresponding author: anna.tramelli@ingv.it