206 A. M. Alekseev et al. 



tectonic zone (Zavodoukovskaia, Komissarovskaia and Kapralikhskaia struc- 

 tures). However, in one case at the section between the township's Bol'shoe 

 Sorokino and Vikulovo an elevation of the electrical marking horizon 

 was observed. The elevation was not reflected in the seismic profile. This 

 fact requires further study. 



Despite the considerable depths of the electrical marking horizon in 

 the Tobol'sk and Vagai-Ishim tectonic zones, the curves of two-way probing 

 have very well defined qualitative features, associated with the non -horizontal 

 nature of the studied surface. Fig. 8 gives as an example of two-way curves 

 for the azirauthal probing along the profile intersecting the Krotovskaia struc- 

 ture. It can easily be seen that here the above-described regularities are 

 maintained in the mutual positions of the right-hand branches of the plus 

 and minus curves. It is obvious that such clear indications are possible under 

 conditions of comparative constancy of the geoelectrical section with regard 

 to the distances, which is characteristic for the territory being studied. 



THE METHOD OF TELLURIC CURRENTS 



The idea of the method of telluric currents was proposed by K. Schlum- 

 BERGER in the thi ties. However, owing to the intensive development in the 

 resistance method, observations on the telluric currents were rarely conducted.. 

 After the war the systematic development of the telluric current method 

 in the USSR was started by the staff of the VNII Geofizika working initially 

 under S. M. Sheinman, and then Alekseev and Berdichevskii (^>. Experi- 

 mental work conducted by jjarties from VNII Geofizika in the Saratovsk 

 Zavolzh'e (1949), the Dneprovsko-Donetsk depression (1952) and the 

 Cis-Baltic depression (1954), gave favourable results and made it possible 

 to change over to the large-scale use of this method. Abroad (^) the method 

 of telluric currents also finds industrial application. 



The use of the telluric current method involves studies of the average 

 periodic variations of the natural non -stationary electrical field of the earth 

 (field of telluric currents) associated with a certain electrical phenomenon 

 in the ionosphere. Telluric currents, embrace the whole of the globe, forming 

 on its surface regional current whirlpools, and have a pulsating character, 

 changing in time, in value and direction. The maximum intensity of variation 

 of the field of telluric currents is usually observed in the period from 1-12 hr 

 (Greenwich Mean Time) <'^>. 



The theory of the telluric current method proposes that within the limits 

 of small areas of the earth's surface, the field of telluric currents at any givea 

 instant of time can be considered as the field of a constant current, caused 



