Namafjall High Temperature Field in N Iceland. A 3D Resistivity Model Derived from MT data

Abstract

Námafjall is a high temperature field situated within the volcanic zone in NE Iceland. Resistivity methods have been used in Námafjall since early seventies, first DC methods, succeeded by TEM (Transient Electro Magnetic) measurements and now MT (Magneto Telluric). A 3D inversion of MT resistivity data from Námafjall, shows a conventional resistivity structure for a high temperature system i.e. a low resistivity cap underlain by a high resistivity core. It also detects a deep seated low resistivity body that may indicate the heat source of the geothermal system. An up flow of heat into the system is indicated by two anomalies, one under Námafjall and another to the south of Námafjall near Hverfjall mountain. The Námafjall low resistivity anomaly domes up to 1500 m b.sl. under Námafjall mountain and seems to indicate the main up flow zone into the geothermal system. The Hverfjall low resistivity anomaly domes up to 3000 m b.s.l. just south east of Hverfjall and may indicate a second up flow zone into the geothermal system. Well data in the area show good correlation between the resistivity model and parameters such as alteration of rocks and temperature.