208 A. M. Alekseev et al. 



are interpreted as zones of reduced total longitudinal conductivity of the 

 succession above the marker horizon and as the zone of elevation of the 

 highly resistant marker horigon. 



The method of telluric currents doesn ot involve a subdivision of the studied 

 cross-section based on resistance, but gives results somewhat dependent 

 on the influence of the horizontal electrical heterogeneity of the conducting 

 sequence. In this connection, it would be desirable to combine the method 

 of telluric currents ^v'ith electrical resistance probings at various sections 

 of the studied area. A combination of the observations on telluric currents 

 with electrical probes not only increases the reliability of the qualitative 

 conclusions on the geological structure of the region, but also makes it 

 possible to carry out approximate quantitative calculations, necessary for 

 conversion from the map of average field intensity of the telluric currents 

 to a schematic structural map of the reflecting highly resistant horizon. 

 With an equally -spaced network of resistance probes, the quantitative interpre- 

 tation of the data of the telluric current method is made by using the empirical 

 formula H = FE", in which the values of F, oc for the whole area of the 

 survey are determined by comparing the average field intensity E of the 

 telluric currents with the thickness H of the conducting sequence at the 

 reflection points (from the data of electrical probes). 



Depending on the character of the territorial distribution of the obtained 

 coefficients, they are either averaged or interpolated. In the case of an 

 extremely sparse network of resistance probes, use is made of the simpler 

 formula H = FJE, which, as sho"\vn experimentally, gives less accurate 

 results. 



It should be mentioned that the quantitative interpretation of data of 

 telluric currents can also be based on the use of values of depths of 

 reflection from the results of seismic exploration under conditions where 

 the seismic and electrical reflecting horizons correspond to the same for- 

 mation. 



In 1955, exploratory observations of telluric currents were carried out 

 by an experimental party of the Siberian Aerogeophysical Expedition of 

 VNII Geofizika in the Tomsk region in the closed polygon Tomsk — Bakchar — 

 Podgornoe — Chezhemto— Mogochin — Shegarskoe of total length 750 km. 

 The observation points were placed at a distance of 10 km from one another. 

 The transport was provided by vehicles which were particularly suitable for 

 rough ground, and when there was no road at all a helicopter was used for the 

 first time, in electrical exploration work. During the survey, the position 

 of the base station was changed after every 30 km. The values of E at tlie 

 base points were equated by the correlation method and then reduced to 



