Electrical features of deep structures of southern Tuscany (Italy)

Over the last six years, magnetotelluric data were acquired at 86 sites covering much of Southern Tuscany. Twenty-four of these sites were acquired in single-site of local-reference mode, whereas 62 were acquired in very-remote-reference mode, with a remote site located on Capraia Island-40 km from the cost- where the cultural noise is very low. The data modelling showed that the Southern Tuscany is characterized by a fairly uniform middle-lower crust that has a resistivity of a few thousand Om below 10 km. At shallower depths in the crust, the resistivity is closer to values around 500 Om. This uniformity is interrupted only below the Larderello and Mt. Amiata geothermal fields where deep conductive bodies are believed to exist. A general anomalous condition can hence be depicted for this region, with low resistivity values typical of those in tectonically active areas as opposed to more resistive values typical in continental areas. These data and those from other geophysical techniques suggest that these conductive zones may be associated with hot material coming from deeper sources below the geothermal areas.