Ambient noise tomography of Campi Flegrei caldera during its most recent unrest

Campi Flegrei is one of the most active calderas worldwide, located west of Naples, Italy, and since 2005 is in the actual unrest phase. This study applies Ambient Noise Tomography to investigate Rayleigh-wave velocity structure of the caldera from 2022 to 2024. By performing cross-correlation of continuous seismic records from stations of the Italian Seismic Network (IV), managed by Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Vesuviano (INGV-OV), and by constructing dispersion curves for each station pair, we derive Rayleigh-wave phase velocity maps at different frequencies (0.25 Hz, 0.50Hz, 0.75 Hz, 1.0 Hz, 1.25 Hz, 1.5 Hz), corresponding to various depths. Our results reveal a clear correlation between phase velocity and seismic activity. High velocities are observed in increased seismicity areas, whereas low velocities correspond to low seismic activity regions. Highest velocities are retrieved in the Pisciarelli/Solfatara area, likely due to fluid migration between Solfatara and Pisciarelli, as well as the presence of shallow faults or aquifer systems. Similarly, between Procida and Capo Miseno, in the centre of Procida canal, we find high velocities, which can be attributed to the presence of a slope and a shallow bank. This study highlights the potential of ambient seismic noise-based tomography for monitoring caldera dynamics and contributes to a better understanding of the structural processes of the current Campi Flegrei unrest.