Mapping bedrock topography and moraine deposits by transient electromagnetic sounding: Oslo graben, Norway

In this research, we have studied the capabilities and limitations of the transient electromagnetic sounding applied to investigate the structure and composition of the moraine deposits covering a crystalline basement. It has been experimentally demonstrated that using the ungrounded antennas one can not only determine the electrical resistivity of different layers in the alluvium deposits and map the surface topography of the crystalline basement down to a depth of 70-100 m, but can also minimize the costs and the damage done to the environment. Additionally, transient electromagnetics helps to reveal the layers within the moraine strata that often have different resistivities and depths. The use of single antennas of size 12 m x 12 m-25 m x 25 m for field excitation and registration of transient responses allows for maximum localization of the targets and provides a high horizontal resolution in strongly heterogeneous media. The limitations of the method due to the induced polarization effect have also been investigated. Overall, despite some limitations, the transient electromagnetic method appears to be effective in the mapping, assessment and analysis of hazards in landslide-prone areas, prior to geotechnical soundings in wells.