Investigation of geothermal structures by magnetotellurics (MT): an example from the Mt. Amiata area, Italy

During 1999 a magnetotelluric (MT) survey was carried out on the southern margin of the Mt. Amiata geothermal region (Tuscany, Italy), with the aim of defining the shallow and deep electric structures related to the local geothermal reservoirs and system heat recharge. Local and remote data were collected along a SW-NE profile and processed with two different robust algorithms. After a detailed study of the EM strike, the data were inverted and two-dimensional (2D) models of electrical resistivity and impedance phase were computed. The interpretation revealed a good correlation between the features of the geothermal field and resistivity distribution at depth. In particular, a shallow conductor (0.5-4 km) detected by the MT survey shows a good correlation with the areal extension of the geothermal reservoirs.