GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.2 GNGTS 2023 Relative earthquake location of low-energy volcanic seismicity at Campi Flegrei S. Danesi 1 , N.A. Pino 2 , S. Carlino 2 , C.R.J. Kilburn 3 1 INGV Sezione di Bologna, IT 2 INGV Osservatorio Vesuviano, Napoli, IT 3 UCL Hazard Centre, Dep. of Earth Sciences, University College London, London UK Introduction The analysis of the distribution of seismicity in a volcanic environment can provide useful constraints for the study of the evolution of active magmatic and hydrothermal processes. This work intends to contribute to the comprehension of the Campi Flegrei caldera (CFc) unrest, through the relative relocation of the diffuse seismicity recorded during the 1982-84 unrest and, later, after 2005, ​ when the ongoing unrest reactivated. The CFc is one of the best monitored volcanic areas in the world, with a multi-parametric network of observing stations operating in the area (Bianco et al., 2022). The shallow structure of the caldera, between 1 and 3 km, is a high temperature hydrothermal system formed by a sequence of volcanoclastic, tuffs, lava and marine deposits. The temperature gradients measured in deep boreholes, down to a depth of about 3 km, exceed 150°C/km; a zone of pressurised gas and sill intrusion is possibly located at 3-4 km (Calò and Tramelli, 2018). In the deep structure (7-9 km), a long-term magma reservoir persistently supplies CO 2 to the surface ( e.g. , fumaroles at Solfatara-Pisciarelli) (Zollo et al., 2008; Carlino et al., 2012). For the ongoing unrest a remarkable correlation between the cumulative number of seismic events, the vertical ground deformation, and the increment of the CO/CO2 ratio in the hydrothermal system has been observed (Tramelli et al., 2021). While the unrest of 1982-84 has been generally associated with magma injection (e.g. Bonafede et al., 2022 and references therein), a mechanism of fluid pressurisation and heating of the CFc hydrothermal system is thought to be the primary forcing of ground deformation and shallow seismicity of the ongoing unrest (Chiodini et al., 2021; Todesco, 2021). Otherwise, the mechanisms that control the interaction between the rising of fluids from deeper volumes and the seismicity within and below the hydrothermal system are still debated (Moretti et al., 2020; Buono et al., 2022; Chiodini et al., 2022).