Ambient noise tomography of the Etna magma system during the 2020-2021 period

We applied ambient noise tomography (ANT) to image Rayleigh-wave phase-velocity variations beneath Mount Etna during the 2020–2021 period, aiming to constrain the deep magma system. Continuous seismic data recorded by the INGV network were processed using the SeisLib Python framework, which automates empirical Green’s function retrieval through cross-correlation and implements a stabilized least-squares inversion for tomographic imaging. The cross-spectrum of two-year-long ambient noise records yielded Rayleigh-wave dispersion curves between 0.10–0.40 Hz. Phase-velocity maps derived at discrete frequencies (corresponding to 2.5–10 s periods) reveal systematic lateral heterogeneities within the studied area. Across the investigated depth range (2–25 km), results reveal a radially symmetric low-velocity anomaly centered near 37°40′ N–14°35′ E. Thanks to the constraints provided by active seismicity, this anomaly is interpreted as a ductile or partially molten region that expands northeastward beneath Mt. Etna from 8–10 km depth. The area remains largely aseismic down to 18 km, below which clustered seismicity likely reflects dike-fed magma ascent. Shallow anomalies (2–3 km) suggest the presence of hydrothermal fluids within the Catania Plain and a rigid intrusive body beneath the volcanic edifice, while intermediate depths (6–10 km) reveal a fractured domain beneath the Nebrodi Mountains consistent with ongoing crustal compression. The southeastern sector remains mechanically rigid and thermally cold throughout, reflecting the structural influence of the extinct volcanic systems.