Installazione di 5 stazioni digitali a larga-banda sull’isola di vulcano: un contributo alla conoscenza della sismicità superficiale della fossa

Abstract

Earthquakes beneath Vulcano (Aeolian Island, Italy) are associated with fracturing (single events and sporadic swarms of low magnitude) or related to processes of the geothermal system (Montalto, 1994). This latter processes is responsible for most of the background activity, which is represented by weak events originating at shallow depth under the La Fossa cone (H<1.5 Km below sea level). In order to improved the Permanent Seismic Network (PSN) run by Catania Section of Istituto Nazionale di Geofisica e Vulcanologia (INGV-CT) by installing additional 5 broad-band stations surrounding the La Fossa crater, to. In particular, on November 2005 along the north rim of La Fossa cone, 3 digital stations were installed with an array configuration; thereafter, in spring 2007 another two stations were installed at the southern base of the cone. All the stations are currently in continual transmission with Lipari Observatory. We considered about 1200 micro-earthquakes recorded from January 2004 to July 2007 associated with fluid dynamics processes. Studying 1007 of these events, six classes of events have been recognized by visual inspection, spectral and cross correlation analyses. Three episodes of increasing occurrence accompanying geothermal and geochemical anomalies have been recorded during this time period. The improved seismic network allowed the location of 55 events with unprecedented resolution and to highlight a space distribution depending on the classes of events. The events are located in the central and south-oriental sector of the cone at 500-1000 meter b.s.l. depth and events of each class seem clustering in preferential sectors.