Three dimensional inversion of magnetotelluric (MT) resistivity data from Reykjanes high temperature field in SW Iceland

Abstract

The resistivity structure of Reykjanes is presented, derived from a three dimensional (3D) model developed in 2016. The model is the final results of a 3D inversion of MT data, corrected for static shift by joint inversion with TEM soundings at the same location as the MT soundings. In the model presented here (REYSAND), a total of 136 sounding pairs are used for the inversion. The model covers Reykjanes area and Sandvík potential geothermal area. The resistivity structure of a high enthalpy system reflects the thermal alteration of the rock. The Reykjanes models reveal a conventional resistivity structure for a high enthalpy geothermal system, i.e. a low resistivity cap underlain by a high resistivity core. The low resistivity cap reaches surface in the hot spring area, Gunnuhver, and dips down in all directions forming an elongated area of 2.5 km × 3 km in strike direction down to 1 km depth bounded by the low resistivity. The resistivity of the low resistivity cap is less 3 Ωm and is underlain by a high resistivity core with resistivity of 10–30 Ωm down to 3 km depth. At greater depth, high resistivity anomalies are prominent with a zone of lower resistivity, in strike direction, under the main field. This zone coincides with an aseismic zone at depth and may indicate a fracture zone with higher temperature and/or permeability within the geothermal system. Comparison to data from the IDDP-2 drilling as well as seismic monitoring confirms that suggestion.