GNGTS 2013 - Atti del 32° Convegno Nazionale

to 1500 tonnes/day of CO 2 emission which are well aligned with the the main fault system and temperature up to 95°C far from the fumaroles (Granieri et al. , 2010). During the first 16 years of systematic monitoring of the geochemical composition of the BG and BN fumaroles, from 1984 to 2000, the CO 2 /H 2 O has shown three clear anomalous ratios, in 1986, 1991 and 1995-96, respectively of 0.30, 0.26 and 0.34 over a background average value of 0.17, peaked about one year later from the corresponding unrest ground deformation. Since 2000 the CO 2 /H 2 O has progressively increased with a nearly linear trend from the background value of 0.17 up to about 0.32 (Chiodini et al. , 2010). The Pisciarelli area is located outside the Solfatara crater. It extends from the eastern slopes of the Solfatara volcano to the western margin of the nearby Agnano crater. The Pisciarelli area is characterised by a fumarole field, which is affected by near-surface secondary processes of seasonal character that seem to mask the deeper signals related to the temperature-pressure changes occurring in the hydrothermal system, clearly observed, instead, inside the Solfatara crater at the BG and BN fumarole vents (Chiodini et al. , 2011). Starting from 2003, the Pisciarelli field has experienced an evident increase of activity, which has been marked by a sequence of temperature peaks of the fumaroles above the average background temperature of 95°C, each lasting up to half a year until early 2011, and exception- ally about one year, from mid 2011 to mid 2012, the last recorded peak. Furthermore, a nearly linear trend of the peak temperatures, from about 97° C up to around 112°C, has been recorded from 2003 up to date. The increase of activity has also been marked by the opening of new vigorous vents and degassing pools, also accompanied by intense local seismic activity (D’Auria et al. , 2011). Fig. 1 – Top: aerial view of the Solfatara crater and surrounding urbanized areas. The white area inside the crater is the vegetation- free degassing area. BG, BN, LS and LF indicate the Bocca Grande, Bocca Nuova, Le Stufe and La Fangaia main fumaroles, respectively, located inside the Solfatara crater. PI indicates the Pisciarelli main fumaroles, located outside the crater. Red and green circlets indicate the CSAMT and combined CSAMT-MT sounding stations, respectively. Bottom: resistivity model obtained from the 1D inversion of the MT data, along the Solfatara-Pisciarelli profile. A common logarithmic scale is used for the resistivity. Black and green triangles along the distance scale indicate the CSAMT and combined CSAMT-MT stations, respectively. 289 GNGTS 2013 S essione 1.3