MT methodology in the detection of deep, water-dominated geothermal systems

A magnetotelluric (MT) survey was performed in an area south-west of the Mt. Amiata geothermal field to assess its usefulness for detecting deep, water-dominated geothermal systems. The survey comprised 28 sites spaced approximately 1 km apart along a SW-NE profile. Two unique aspects of the data collection included (1) a remote reference site located 50 km away on the island of Capraia, and (2) contiguous telluric dipoles between each of the 28 main sites for a continuous MT profile. Data from a far remote site were used in conjunction with robust processing algorithms to remove low frequency coherent electromagnetic noise, generated by electrified railways, from the local data. A continuous profile of MT data resulted in greater resolution of the subsurface electrical conductivity and prevented spatial aliasing problems. Two dimensional (2D) models of electrical resistivity were merged with gravity, seismic, thermal and structural data. The integrated interpretation of these data resulted in an accurate reconstruction of the main geological features and the detection of deep horizons due to the presence of geothermal systems. Deep and shallow conductivity anomalies detected by the MT survey can be correlated with fractured areas of the geothermal reservoir and with the possible presence of a deep partially molten granitic body. From this reconstruction, the geothermal reservoir already under exploitation in the Mt. Amiata area seems to extend to the SW, expanding the possibility of geothermal exploration in southern Tuscany