New Technology and Methods for Characterizing the Seismic Hazard and Active Hydrothermal System beneath Lipari Island, Italy

We plan to study the seismic structure of the active hydrothermal system beneath Lipari Island (Aeolian Islands, Italy) and produce a detailed velocity model that will be useful for assessing the seismic hazard. The Aeolian Islands consist of a 150-km long volcanic arc and are located between the Southern Tyrrhenian Sea backarc basin and the Calabrian Arc. The Aeolian volcanoes were emplaced on 15 to 20 km thick continental crust and the ages of their volcanic products range from 1.3 Myr to the present. The volcanism started during the Pliocene, migrated southeastward, and is still active in Stromboli Island located in the easternmost portion of the arc. Lipari and Vulcano are instead characterized by hydrothermal activity. The Lipari fumaroles, including the St. Calogero geothermal area, are located in the western part of the island, where kaolin has extruded due to the hydrothermal alteration of pre-existing lava flows and pyroclastic fall and flow deposits. Fumaroles and active soil degassing from fractures and faults are common in the hydrothermal area.

A recent study has shown that a decrease in fluid discharge may reflect pressurization at depth that potentially precedes hydrothermal explosions. The object of this study is to further our understanding of these processes by providing detailed images of the subsurface structure of Lipari Island. We will record ambient noise and local seismicity over a time period of 35 days using 50 cable-free, self-contained seismic instruments (nodes) with 5 Hz corner frequency. The array will have a roughly semicircular geometry in and around the hydrothermal area, with the final configuration determined strictly by the topography. Seismic data will be merged with the surface lithology, faults and fractures, and volcanic structures mapped during the seismic acquisition, and interpreted along with measurements of the CO₂ gas flux from the study area. The combined analysis of simultaneous measurements of CO₂ gas release and seismic properties will provide information on the dynamics of fluid ascent and pathways. Results from this study will improve our understanding of the fluid dynamics at shallow depth and the unrest episodes in active volcanic and hydrothermal areas.