Transient Electromagnetic Resistivity Survey at the Geysir Geothermal Field South Iceland

Abstract

A central loop Transient Electromagnetic TEM Resistivity Survey was conducted at the Geysir high temperature geothermal area as part the project of the author. The area is situated 110 km away from Reykjavik and lies in a shallow valley elongated north-south. Geologically it is surrounded by three volcanic domes made-up of rhyolites, hyloclastites and inter-glacial basaltic lava that obtain heat from an intrusive body. As a result of this survey a high resistivity temperature field is revealed beneath Geysir. The resistivity of the earth reflects the thermal alteration of the rock. High resistivity at the surface reflects fresh lava and low resistivity reflects water saturated rocks situated below the water table.
The high temperature field is characterized by a low resistivity cap underlain by high resistivity without confirmed evidence. This resistivity reflects the thermal alteration of the rock dependent on temperature. Hence, provided there is equilibrium between alteration and temperature, the resistivity measurements indicate temperature. The benefit of central loop TEM sounding method over the conventional DC method is clearly stated.