Relationship between micro-shocks recorded on the island of Vulcano (Italy) and meteorological parameters

Swarms of micro-shocks having low magnitude (B0), and duration between 2 and 4 seconds are often recorded at Vulcano in the Aeolian Archipelago (Italy) close to Gran Cratere which is the most recent eruptive edifice of the island. This study describes the characteristics of such peculiar seismic events, and examines their relationship with meteorological parameters. The set of shocks considered spanned from 1984 and 1990, and is here analyzed along with the daily values of temperature, barometric pressure, humidity, and amount of rainfall. The meteorological parameters were recorded at a station which was located a few kilometers from Gran Cratere. On the basis of their features, seismic events were divided into two groups: one showing a monochromatic character with a dominant spectral peak at 9.4 Hz, the other having a wider spectrum with dominant peaks in the range between 7 and 14 Hz. From the cross-correlation analysis of seismic and meteorological data a seasonal distribution of the occurrence of such micro-shocks can be surmised. Significant relationships with a 99% confidence level were found with all meteorological parameters. In particular, rainfalls precede with a short-time interval (about one day) the occurrence of these swarms. This result inferentially leads to an origin of such shocks in the surficial part of the volcano, and a source mechanism which may be linked to activation of microfractures induced by the action of meteoric water.