Distortions of the electromagnetic field by shallow basins and by resistive outcrops

The interpretation of magnetotelluric (MT) measurements carried out on shallow (several hundred metres deep) basins and on the surrounding highly resistive rock outcrops can be difficult due to different forms of distortion, mainly 3D effects. A good example for study of this problem is the Mór Graben, which is the transition zone between the Bakony and Vértes Mountains (W-Hungary), where more than 20 MT soundings have been made with stations spaced about 2 km apart to determine the structure of a conductivity anomaly at a depth of about 3–4 km.

The statistical treatment of the different distortions due to varying sediment cover (the S-effect or static shift) and to the steep wall of the resistive basement outcrops (edge effect), etc., enabled the estimation of the actual parameters of the conductive formation. The interpretation of the field data is supported by numerical modelling.