| Abstract: | As a contribution to the EEC study of the potential contribution of electric and electromagnetic techniques to geothermal exploration, magnetotelluric studies have been undertaken with a sounding bandwidth ranging from 2 to 7 decades of period at more than 30 sites within the chosen test area of Travale. This area must be one of the most unfavourable for the application of electrical techniques on account both of the thickness (up to 2 km) of conducting (< 1 ohm · m in some locations) cover formations and of the intensity of the artificial disturbances from local power stations and distribution lines. Nevertheless it has been possible to obtain good quality data over part of the sounding band employing an automatic in-field analysis system and rigorous data analysis and to penetrate to reservoir depths at the centre of the graben by undertaking broadband soundings (up to 10' s) at some sites. For interpretation of the data for periods up to about 100 s, 2-D modelling is both satisfactory and essential (1-D modelling provides correct layer resistivities but underestimates interface depths) and good agreement has been obtained for an electrical structure model and the relevant geological section. The 2-D models, which best fit the long period data, are characterised both by zones of highly conducting flysch cover formations and by an anomalously conducting basement. Restriction of the study to a test area within the Travate graben inhibits the unequivocal association of these conducting zones with the thermal anomaly. |
