Ambient noise surface wave tomography of Mt. Etna volcano structure during 2020-2021

Velocity tomography, superposed with local seismicity, provides key spatial constraints on the inner structure of an active Volcano such Mt. Etna Volcano. We present the results of an Ambient Noise Tomography carried out via SeisLib to retrieve Rayleigh surface-wave velocity models across the East Sicilian crust at multiple frequencies, each sampling different depth ranges.

Two years (2020-2021) of continuous vertical-component data from 12 INGV stations were analysed. Their spatial configuration minimizes volcanic tremor while maximizing interstation paths beneath Mt. Etna. The selected period is seasonally balanced and free of major eruptive activity. The frequency range (0.10-0.40Hz) for the Rayleigh-wave velocity models was chosen to isolate ambient noise generated by ocean-lithosphere interactions. For each frequency at which a Rayleigh-wave velocity model is retrieved, local seismicity within the corresponding depth range, identified through associated sensitivity kernels, are superposed.

Across the investigated depth range (2–24km), results reveal a low-velocity anomaly beneath Mt. Etna western flank, whose significance varies with depth. At shallow levels (<5km) it is in good agreement with the low-cohesion sediments of the Caltanissetta Basin. At 8–10km depth, the increasing temperature gradient suggests a possible ductile or partially molten volume trending northeastward. This volume remains largely aseismic down to ~18km, below which clustered seismicity is likely related to magma migration at ~23km.

Shallow low-velocity anomalies (~2–3km) beneath the Catania Plain are in good agreement with the hypothesized presence of hydrothermal fluids, supported by the Salinelle di Paternò mud volcanoes, while a moderately high-velocity anomaly beneath Mt. Etna is consistent with a mechanically stiff body, most likely an intrusively cooled magmatic intrusion. At intermediate depths (~5–10km), a low-velocity anomaly beneath the Nebrodi Chain, overlapping with seismicity, might reveal a fractured domain consistent with ongoing deformation processes. The southeastern sector is characterized by high seismic velocities, consistent to a mechanically rigid and thermally cold crust associated with extinct Hyblean volcanism.

Future developments will incorporate Love-wave dispersion to enable a joint Rayleigh–Love inversion, yielding a high-resolution Vs model with enhanced depth and lateral coverage. Coupling these results with constitutive-relation frameworks and computational thermodynamics will enable the development of a petrophysical inversion scheme, providing new constraints on the inner structure of Mt. Etna Volcano.