Seismic tomography investigation at the Lipari-Vulcano complex (South Italy) provides new insights on the active degassing system

Seismic tomography represents a very powerful and effective tool to look at depths beneath volcanic systems thus helping to better understand their behavior. In particular, a key parameter useful to discriminate the presence of gas, fluids and melts is represented by the P-wave and S-wave velocity ratio. In the present study, we collected ~ 4400 crustal earthquakes that occurred in the last thirty years and we used the LOcal TOmography Software LOTOS to estimate the first 3D overall model of Vp, Vs and Vp/Vs for the Lipari–Vulcano complex belonging to the Aeolian islands system (southern Tyrrhenian sea). The investigated area has been characterized both in old and recent times by fumaroles, hydrothermal activity and active degassing. In particular, in the past decades several episodes of anomalous increases of fumarole temperature and strong degassing have interested the Vulcano Island, the latter of which started in September 2021.

The results of the tomographic investigation indicate the presence of two main anomalies of low Vp and low Vp/Vs, clearly depicted up to ~ 8 km depths, and related to gas-rich materials beneath the central-northern sector of Vulcano and the western off-shore of Lipari, respectively.

The anomaly beneath Vulcano is located in close correspondence with La Fossa caldera area and with the sector where fumaroles, hydrothermal activity and active degassing are widely documented. Moreover, beneath the western Lipari off-shore a new, previously undetected, volume of strong gas-concentration has been identified. Even if these two anomalies show almost the same intensity, no evidence of degassing activity is available for the latter one because of its location at sea depths where the relevant water column pressure may inhibit the observation of possible degassing processes.

The obtained results furnished a picture of the spatial distribution of gas-filled volumes feeding the main degassing activity of the Lipari-Vulcano complex and allowed to highlight the main role played by volcanic gas in the whole system, thus furnishing invaluable constraints for improved modelling of the volcanic system and of its possible evolution.