NEW METHODS OF ELECTRICAL EXPLORATION IN SIBERIA 199 



several quadrilateral and aziniuthal probes were carried out with coincident 

 centres. The results obtained were sufficiently close to one another. 



In 1956, curved azimuthal probings were carried out in the Tobol'sk and 

 Vagal' -Ishim tectonic zones (Tyumensk region) in localities characterized 

 by a depth of the reflecting level of 1200 to 2500 m. The studies were car- 

 ried out over a route about 250 km long. The maximum distances between 

 the dipoles of the azimuthal arrangements were between 8 and 10 km. 

 The field laboratories moved along winding roads. Despite the fact that 

 owing to the frequent rains, the road conditions in a number of regions 

 were bad, the party was able to carry out more or less regularly one two- 

 way probing in one working day equivalent to two AMNB probings with 

 maximum spacings of AB = 16-20 kin. The curves of the azimuthal probing 

 agree sufficiently well mth the curves for quadrilateral probing. The oscillo- 

 grams referring to the large dispersions of the azimuthal probing were 

 worked out with a sufficient degree of accuracy. 



As well as with the azimuthal arrangement tests were made using a radial ar- 

 rangement and a parallel arrangement, with small angle 0, making it possible 

 to obtain results which practically coincided with the results of the radial 

 probes. These studies were also carried out over curved routes. With radial 

 and especially with parallel probes, it was much easier to unreel the wire. 

 However, due to the reduced depth of the study, these methods under 

 conditions involving an electrically reflecting level at a great depth were 

 used in an auxiliary capacity. 



The work showed the effectiveness of using the irxethod of two-way elec- 

 trical probes for surveying upfolds in the top surface of the marker 

 horizon, which in a number of sections of the Western Siberian Lowlands 

 represents the top surface of the Paleozoic deposits. It was also shown that in 

 zones of sedimentary and volcanic layers of the second structural level 

 the stratigraphic- position of the electrical marker horizons can change 

 depending on the degree of metaraorphism of the sedimentary rocks, and 

 the presence of volcanic formations in them. In this case, the data of the 

 electrical survey reflect the changes in the thickness of the conducting part 

 of the section, which is represented by friable, weakly -metamorphized arana- 

 ceous argillaceous deposits, devoid of widespread intrusive sills. 



The curves of two-way electrical probing can be interpreted more re- 

 liably than the curves of the vertical electrical probe and give fuller infor- 

 mation about the nature of disposition of rocks. The methods of qualita- 

 tive and quantitative interpretations of electrical probe curves in two-way 

 measurements are supplemented by an analysis of the divergence of posi- 

 tive and negative KS curves. This divergence is caused by the dip of the 



