Indagini VLF-EM per la mappatura della risalita di acque profonde ad elevata salinità in Oltrepò Pavese; risultati preliminari

The Oltrepò Pavese plain (Northern Italy) is characterized by the uprising of high mineralized waters from the marine substratum. These Na-Cl rich waters, mix with the shallow ground waters of the aquifers and pollute them, preventing their use. This phenomenon is connected to the presence of the “Vogherese Fault”, a buried tectonic discontinuity, along which the saline waters are distributed. A VLF-EM survey carried out along the “Vogherese Fault”, indicates that high mineralized waters uprising gives rise to high electrical conductivity anomalies where the marine substratum is shallower. Different algorithms, were used for the asymmetry inherent in dipangle data remotion, noise reduction and low pass filtering. Currentdensity pseudo-sections and a contour filtered dip-angle map of the area obtained by the in phase and out of phase quadrature fields, show that strong anomalies are localized along the fault surface trace. Furthermore, there is a clear correspondence between the spatial distribution of conductivity anomalies and the monitored wells and low resistivity anomalies found by VES surveys. The use of VLFEM data integrated with electrical resistivity sounding, allowed the surface and in depth mapping of the complex geometry with which the high mineralized waters uprise along the fault zone.