Three-dimensional conductivity model of the Sabalan geothermal field, NW Iran, interpreted from magnetotelluric data

Abstract

Magnetotelluric (MT) data were used to infer an electrical conductivity model of the Sabalan geothermal field (NW Iran). It is associated with a stratovolcano and significant surface manifestations frequently occur. Based on the results of data analysis, an east–west direction was identified as the dominant electrical strike in the area and two-dimensional inversion was applied. Also, three-dimensional inversion was accomplished to deal with some three-dimensional effects, which were indicated by data and are common in the complicated geological setting of geothermal reservoirs. The obtained models reveal the presence of a very resistive thin cover down to about 300 m, due to the unaltered basalts, underlain by a highly conductive layer. The most prominent characteristic of the model is the thoroughly variable thickness of the conductive layer. This layer—which is related to the different levels of thermal alteration—persists at depth and can be interpreted as outflow region. At shallow depths, there is a consistency between resistivity distribution derived from MT data and the general conceptual model proposed for high-enthalpy geothermal systems. The deeper electrical structure was found to be more resistive (100 Ω) due to the presence of metamorphic rock formations.