DC Resistivity at the Ahuachapan Geothermal Field, El Salvador

Abstract

Deep dc resistivity surveying has been performed at the Ahuachm Geothermal Field in wHem El Salvador. The field lies on the north base of the volcanic range t h l funs the length of the country and is the site of a significant active geothermal powerplant. The technical purpose of the surveying was to assess the geophysical properties of the geothermal regime amund the existing field. The survey was carried out as a colinear dipoiedpole survey using dipole spacings of 500m and 1000m, and dipole separations of up to fourteen dipole lengths. Results included (1) the observation that the geothermal reservoir was not eadily detectable due to surface lithologic changes and extensive cultural effects, (2) the hydrothermally altered areas are readily reccgnked by their low resisthrities, (3) kcal lithologies appear to be mappable based on their b situ resistivities, (4) the greater field logistical convenience of the shorter 500m dipole spacings is negated by the Increase in topographic effects, and (5) 1( appropriate dipole separations am used, there Is no need to tun surveys of both 500 and lo00 meter dipole spacings to gather shalbw and deep information.