GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.3 763 1.5, 1 and 0.5, in case of sphere, horizontal and vertical cylinder, respectively. Interestingly, the numerical analysis finds optimal values for the shape factor p very close to 1.0 for all the three hypothesized sources, suggesting horizontal cylinder-shaped structures as the most probable SP anomaly sources. Such a finding leads to interpret the observed anomalies as horizontal flow pathways, also suggested by the ERT results. Application to multiple SP anomalies observed in a volcanic area. In last decades, in the attempt to characterize the feeding system of Mt. Somma-Vesuvius, many geophysical studies have been carried out, among which SP surveys (Di Maio et al. , 1998). Indeed, SP anomalies in volcanic areas are of great interest, as they can give information on preferential fluid flows along complex crack patterns induced by volcanic and tectonic processes. In particular, to better characterize the anomaly sources found by Di Maio et al. (1998) along the SW-NE SP profile shown by red dots in Fig. 2, the GPA analysis has been performed by assuming models given by multiple SP sources with different geometries resembling dyke- or fault-type structures. The best results have been obtained by using a four sheets model defined by the forward function: where x 0j and z 0j are the horizontal positions and the depths of the sheets centers, respectively, a j are the half-width of the sheets, and θ j are the sheet inclinations with respect to the horizontal axis. Interestingly, the GPA curve is able to reproduce some of the main feature of the experimental curve as shown in Fig. 2. In particular, the numerical analysis finds optimal values for the location, orientation and depth of the inclined sheets which correlate well with structural lineaments delineated by previous geophysical and geostructural studies (De Natale et al. , 2004; Milia et al. , 2012; Tramparulo et al. , 2018). References Biswas A. and Sharma S.P.; 2014: Resolution of multiple sheet-type structures in self-potential measurements. Earth Syst. Sci., 123 , 809–825. Brachetti P., De Felice Ciccoli M., Di Pillo G. and Lucidi S.; 1997: A new version of the Price’s Algorithm for Global Optimization . J. Glob. Optim., 10 , 165–184. Fig. 2 - SP data (red dots) and GPA curve (blue line) obtained for a four-sheet model.