Electrical resistivity surveys, ascension Island, South Atlantic Ocean

Reconnaissance electrical resistivity surveys, completed on Ascension Island as one part of an integrated geothermal exploration program, define a 5 km 2 area of low resistivity within the central part of the island. Dipole-dipole lines help to define the vertical resistivity structure and suggest the incursion of seawater beneath much of the area surveyed. A zone of 5-10 l~m indicated by numerical modeling suggests possible alteration and geothermal brines that may have mixed with seawater, above a geothermal reservoir. Temperature gradients in shallow drillholes and a deep exploration well indicate the presence of a deep geothermal system in this area. Copyright © 1996 CNR. Published by Elsevier Science Ltd.