MT studies in Bulgaria

Early in 2004 the Nordwest Ltd carried out the array MT sounding at Dobrich area in the North-West Bulgaria.

Measurements were performed at a network of latitudinal and longitudinal profiles with 500 m spacing of measurement sites. A total of 580 measurement sessions were accomplished.

It should be mentioned that the electromagnetic prospecting carried out at Dobtich region are unique in both the volume and quality of observations.

The main task of this survey was to study the lower-carbonaceous sediments that had been supposed to lie at depths of 2-3 km in the Vranen horst region.

Quantitative interpretation involved fitting the inversion results for individual curves to the data for the whole area. The obtained results are presented as cross-sections along separate profiles and maps at different depths. The results of electromagnetic prospecting agree quite well with the drilling data available and with the seismic results (at least, as to the upper reflective horizons).

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The interpretation results were used to construct the resistivity cross-sections along 15 latitudinal and longitudinal profiles and the resistivity maps at various depths. Most meaningful are the resistivity cross-sections along longitudinal profiles crossing the main tectonic units at the region of interest.

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Five main geoelectric complexes are distinguished within the sedimentary strata: three high resistive and two conductive. The lower conductive complex is associated with terrigene sediments dated as Lower Carbonaceous rocks.

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Contoured in the central part of the region under study is the structure seen as a highly resistivive unit at depths of 1-1.5 km and as a conductive zone at depths of 2.5-3 km. In plan this structure is located in the central and south-east parts of the area, and in its eastern part this structure coincides with the unit detected by seismic methods. Schematic cross-sections along and across the given structure are shown on the left (the cross-sections are based on the electromagnetic prospecting results).


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