The Application of Audio-Magnetotelluric Surveys on Sao Miguel Island, Azores Portugal

Abstract

Geothermal exploration and development has been under way on Sao Miguel island, Azores since 1975. This work had been restricted to the Fogo volcano, one of three dormant silicic volcanic centers on the island, with most of the work centered in a 10 km2 area at low elevation on the north slope. The USGS in 1982 and 1983 conducted reconnaissance natural source audio magnetotelluric (AMT) surveys of all three silicic centers to evaluate the potential for geothermal systems at each and to demonstrate the utility of the method in areas of difficult terrain. Results on Fogo showed a low resistivity trend extending from the present production area upslope to the caldera boundary. We infer that the upper part of this trend is the upwelling zone of a thermal plume which supplies the production area. Further exploration and drilling are now planned for this area. Other promising regions were defined on the south slope of Fogo and on the other two volcanoes.