Resistivity survey in the Hengill area, SW-Iceland

Abstract

Geophysical methods are powerful tools for characterizing geothermal structures at depth. One of these is the TEM method that is an important electrical method in outlining geothermal resources. TEM soundings have proven to be more downward focussed than the traditional DC-soundings and have a better resolution at depth. The resistivity structure of high-temperature geothermal systems is generally characterized by a low-resistivity cap underlain by a high-resistivity core. Here the results of a detailed TEM resistivity survey in the south-western part of the Hengill volcanic system are described. This survey was an addition to an extensive geophysical survey of the Hengill geothermal area with resistivity soundings added in the southwest part of the area. The TEMTD interpretation program was used to perform 1D inversion on the TEM data. A new iso-resistivity map of the Hengill geothermal system is presented. The results revealed an extension of the geothermal field to the southwest along the fissure swarm connected to the Hengill volcanic system. The high-resistivity core extends along the fissure swarm and reaches an elevation of approximately 100 m b.s.l. This resistivity survey supports the existence of a substantial high-temperature geothermal reservoir in the southwest part of the Hengill central volcano.