GNGTS 2014 - Atti del 33° Convegno Nazionale

relatively close to one another; if the electrode pair is widely spaced it is referred to as a bi-pole. The convention for a dipole-dipole electrode array is to maintain an equal distance for both the current and the potential electrodes (spacing = a ), with the distance between the current and potential electrodes as an integer multiple of a . The electrodes do not need to be located along a common survey line. A primary advantage of the dipole-dipole electrode array is the ease of deployment in the field due to shorter wire lengths. However, a large generator may be needed to transmit a greater current magnitude for the measurement, especially for deep soundings. The dipole-dipole source-receiver coupling has been chosen because of its greater compactness and sensitivity to both lateral location and depth evaluation of anomaly source bodies (Ward, 1990). As source we used the IRIS Syscal Pro ® system with maximum output voltage and current of 800 V and 2 A, respectively. The profiles were acquired in January 2013, in January, March, May, July and September 2014 respectively. They cross the Pisciarelli area following approximately the NS direction and were characterized by a 2.5 m electrode spacing (Fig. 1b) and maximum penetration depth of about 20 m. The ERT lines have singularly been inverted using the RES2DINV ® commercial software (Loke and Barker, 1996; Loke, 2012). The resulting 2D resistivity sections are shown in Fig. 2. In order to highlight the dynamic of Pisciarelli area, we show in Fig. 3 two distinct sections evidencing the resistivity changes related to some of analysed times. Annual changes are reported in the first section, whereas in the second section a two-months interval has been considered. A zone where resistivity increase appears at about 10 m depth in the central part of the survey. This feature appears in both sections mud pool resulting more evident in the period January-March 2014. In the proximity of the principal vent of Pisciarelli, an ulterior resistivity increasing emerges. Finally, in an almost uniform layer, at bottom of the second section, a further resistivity enhancement is present. Fig. 3 – Two distinct sections evidencing the resistivity changes related to analyzed times are shown. Annual changes are reported in the first section, whereas in the second section a two-months interval has been considered. GNGTS 2014 S essione 1.3 215