NEW METHODS OF ELECTRICAL EXPLORATION IN SIBERIA 209 



the original base station which made it possible to construct a combined 

 map of the average intensity of the field of the telluric currents. 



The field of telluric currents in Western Siberia in the summer of 1955 

 was characterized by a more or less intense variation with a period of 10-40 sec 

 and an amplitude of the order of 1-2 mV/km. The maximum variation as 

 a rule was observed in the daylight hours (9-15 hr). A periodic weakening 

 was observed in the variations of the field of the telluric currents up to 

 complete extinction (during August, September and October there were 

 10 such days). 



Fig. 9. L-shape arrangement. 



The measurements were carried out with L-shape arrangements with 

 measuring lines between 300-500 m long (Fig. 9). For synchronization of 

 the observations a specially developed interference -free TB-6 Tele-switch 

 was used in circuit with an RPMS radio station (^). EPO-4 oscillographs 

 were used to record the variations in the telluric current fields. 



Fig. 10 shows the graph for the average field intensity of the telluric 

 currents on the Tomsk -Bakchar profile, constructed on the assumption that 

 the value E at point 24 is equal to one arbitrary unit. The values of E along 

 the profile decrease regularly from Tomsk to Bakchar, changing more than 

 four times. The character of the decrease in the average field intensity of 

 the telluric current agrees well with known geological data and corresponds 

 to a rapid increase in thickness of the sequence at the north-west limb of 

 the Koly van'— Tomsk upfold, there being a clearly defined steplike lowering 

 of the Paleozoic foundation in the immediate vicinity of Tomsk, and also 

 between the villages Markelevo and Plotnikovo. 



There is an interesting local maximum of average field intensity in the 

 region of the points 15, 16, showing the possible presence here of an elevation 

 of the Paleozoic foundation. It is interesting to notice that in this region, 



Applied geophysics 14 



