High precision locations of long-period events at La Fossa Crater (Vulcano Island, Italy)

Abstract

Since the last eruption in 1888-90, the volcanic activity on Vulcano Island (Aeolian Archipelago, Italy) has been limited to fumarolic degassing. Fumaroles are mainly concentred at the active cone of La Fossa in the northern sector of the island and are periodically characterized by increases in temperature as well as in the amount of both CO2 and He. Seismic background activity at Vulcano is dominated by micro-seismicity originating at shallow depth (<1-1.5 km) under La Fossa cone. This seismicity is related to geothermal system processes and comprises long period (LP) events. LPs are generally considered as the resonance of a fluid-filled volume in response to a trigger. We analyzed LP events recorded during an anomalous degassing period (August-October 2006) applying a high precision technique to define the shape of the trigger source. Absolute and high precision locations suggest that LP events recorded at Vulcano during 2006 were produced by a shallow focal zone ca. 200 m long, 40 m wide and N30-40E oriented. Their occurrence is linked to magmatic fluid inputs that by modifying the hydrothermal system cause excitation of a fluid-filled cavity.