The Milos geothermal field: modelling and interpretation of electromagnetic induction studies

Abstract

The magnetotelluric (MT) technique in the period range 10 −2 to 10 +4 s has been applied to determine the electrical structure of the geothermal field of Milos island, Greece. Data from 39 stations have been processed using standard tensorial techniques and the data have been found to be nearly one-dimensional (1D) up to 10 s. Several 1D modelling techniques have been applied to the processed data sets. Subsequent two-dimensional (2D) finite difference modelling has revealed some deeper electrical features. The 1D and 2D electrical models are in agreement with the existing geothermal model. On Milos, within the uppermost 200 m, the resistivity can be < 0.5 ω m. This is explained by the presence of alteration clay minerals. The crystalline basement has resistivities of 10–150 ω m. These anomalously low values of resistivity for basement rocks require the presence of fluid-filled fractures. Study of the azimuths of the major axes of the MT impedance ellipses and the Parkinson induction arrows leads to some tentative association with local and regional tectonics which are related to the subduction and distensional processes taking place in the Aegean.