Detection of Fault Zones Using Electric and Electromagnetic Methods

In the frame of this project electric and electromagnetic prospection methods are investigated concerning their ability to image geological fault zones in depths of interest for geothermal applications. For large-scale geologic structures with depths up to a few km, e.g. fault systems, resistivity can become a valuable key parameter, because low resistivity is an indication for the presence of conductive minerals and/or brines within fractures and hydrothermal fluids

Numerical and practical investigations are carried out with emphasis on the comparison of the possibilities and limitations of the methods used. Electric and electromagnetic methods are jointly operated at selected fault systems and interpreted alongside with seismic data. Initially, well-known shallow fault zones are considered. At a later stage of the project the exploration will be extended to deeper structures. The evaluation of a suitable field survey design and interpretation for a joint operation of these methods is envisaged.

First result of the large-scale DC resistivity (section) and the large scale TEM survey (layered models). The investigation depth reaches about 600 – 800 m. The assumed fault zone can be mapped well, additional seismic structural information (black lines) was added to the interpretation. The 2d interpretation of the DC resistivity shows the fault structure, while layers with low resistivity determined by the TEM fit to the seismic structure.

In the ongoing project the application of very large-scale DC and of the Magnetotelluric method is envisaged for obtaining greater investigation depths. A concept for a suitable field survey design will be evaluated, supported by modelling studies especially adapted to the specific geological features in Northern Germany. Overall aim is the application of a joint strategy for the investigation of fault zones by electric/electromagnetic measurements.