Application in geological and hydrological investigation

Geophysical survey techniques make it possible to map the geological structure of the subsurface to a depth of several kilometres. A continuous image of the underground is created without having to do numerous deep drillings or probings.

Possible applications of geophysical techniques in geological investigation are:

  • mapping the geological structure of the subsurface,
  • mapping dike composition,
  • mapping of impermeable (clay)layers,
  • mapping of aquifers,
  • determination of pleistocene-holocene transitions, 
  • detection of salt domes or caverns,
  • detection of deep oil and gas reservoirs,
  • Detection of conductive structures as for example mineral ores,
  • surveying of salty seepage water.


Seismic research is generally used to map deeper geology and, for example, salt domes. The disadvantage of seismic techniques is that the contrast between the different soil layers and structures or the depth range are insufficient to obtain an accurate image of the substrate.

In most cases the depth range and accuracy of magnetotellural measurements is much more favorable. This technique can replace seismic research, but as a rule it is used in combination with seismic research.

Research objective
The objective of this study was te mapping of a salt dome up to a depth of several kilometers. The salt dome is filled with salt water and the top of the salt dome is expected to be located at a depth of around 500 meters.

Execution
The research was conducted with the magnetotelluric (MT) technique. Electromagnetic loops are laid out on the surface and extensive measurements are performed.

Result
The figure shows the results of the magnetotelluric survey. A salt dome has been mapped to a depth of almost two kilometers. An area of ​​over 1500 meters was investigated.

The blue colors represent a soil composition with a high electrical resistance compared to the surroundings. The red and yellow colors relate to soil material with a low resistivity (and therefore high conductivity).

In the figure a contour is drawn within which the deep subsurface composition has a resistance value of more than 2 Ohm meters. This contour corresponds to the true position of the salt dome. The objective of this study was te mapping of a salt dome up to a depth of several kilometers. The salt dome is filled with salt water and the top of the salt dome is expected to be located at a depth of around 500 meters.