Multidimensional inversion of MT data from Krýsuvík high temperature geothermal field, SW Iceland, and study of how 1D and 2D inversion can reproduce a given 2D/3D resistivity structure using synthetic MT data

Abstract

Electromagnetic (EM) methods are frequently used in the exploration of geothermal resources for determining the spatial distribution of electrical conductivity. Of the various EM methods, magnetotelluric (MT) method was found to be the most effective in defining a conductive reservoir at a depth exceeding 1 km overlain by a larger and more conductive clay cap. The two main objectives of this study are: firstly to explore how 1D and 2D inversion can reproduce a given 2D and 3D resistivity structure using synthetic MT data and secondly to investigate the subsurface resistivity distribution of Krýsuvík high-temperature geothermal field in SW-Iceland, using multidimensional inversion of MT data. The 2D and 3D synthetic models considered in the study were better reproduced by 1D inversion of the determinant of impedance tensor and 2D inversion of TM mode data than by 2D inversion of TE mode and combined TE and TM mode data. 1D and 2D inversion of MT data along two profiles and 3D inversion of 58 MT sites were performed in Krýsuvík area. In the 1D inversion of MT data, transient electromagnetic (TEM) data from the same location as the MT soundings are jointly inverted in order to correct the static shift in the MT data. The 2D and 3D inversion of MT data were performed on previously shift corrected MT data. The full impedance tensor elements were used in the 3D inversion of MT data. The Atlantic Ocean was included as a fixed feature in the 2D and 3D inversion to account for the effect of the highly conductive ocean on MT measurements. The 1D and 2D inversion of MT data from Krýsuvík high-temperature geothermal field revealed three main resistivity structures down to a depth of 10 km: a high-resistivity surface layer underlain by conductive layer followed by high resistivity. The 3D inversion confirmed this main result. In addition, the 3D inversion model showed a low-resistivity .......