GDS (Geomagnetic Depth Sounding) in Italy: applications and perspectives

Abstract

The analysis of geomagnetic field variations is a useful tool to detect electrical conductivity contrasts within the Earth. Lateral resolution of outlined patterns depends on the array dimensions and density of measurement sites over the investigated area. The inspection depth is constrained by the period of geomagnetic variations considered in data processing. Regions with significant geological features such as boundaries of continental plates, marginal areas of contact between tectonic units or other geodynamical processes, are of primary interest for the application of the MagnetoVariational (MV) method. In the last ten years, in the frame of the ElectroMagnetic (EM) sounding techniques in applied geophysics, this method has been applied in Italy by researchers of the Istituto Nazionale di Geofisica, Rome, the Dipartimento di Scienze della Terra, Universitá di Genova and the Czech Science Academy of Prague. The Ivrea body in the Northwestern Alps and their junction with the Apennine chain, the micro-plate of the Sardinian-Corsican system and, recently, the central part of the peninsula along Tyrrhenian-Adriatic lithospheric transects were investigated. Studies in time and frequency-domain used in the first investigations, have been followed by more refined analysis involving tests on the induced EM field dimension, computations of single site Transfer Functions (TFs) through Parkinson arrows' and Fourier maps in the Hypothetical Event technique (HE). It was possible to describe the electrical conductivity distribution in the inner part of the SW Alpine arc and to confirm the presence of lithospheric and asthenospheric anomalies obtained by other geophysical methods. For the Sardinia-Corsica system, 2D and 3D inversion models highlighted the existence of two major conducting bodies, one north of Corsica, and the other south of Sardinia. In Central Italy, the regional electrical conductivity distribution pointed out a deep conductive structure beneath the Apennines and a very resistive root for this part of the mountain chain.