NEW METHODS OF ELECTRICAL EXPLORATION IN SIBERIA 197 



out a considerable extension of electrical exploration in the rather in- 

 accessible regions of Siberia. 



The present article deals with the basic residts of the studies. 



THE METHOD OF TWO-W AY ELECTRICAL PROBING 



The theory of two-way electrical probing by dipole instruments was de- 

 veloped by L. M. Al'pin between 1948 and 1950 ^^K In subsequent years, in the 

 VNIIGeofizika a method was developed for the practical use of two-way 

 probes with quadrilateral* arrangements. This has now been put into prac- 

 tice in geophysical studies over the territory of the European part of the 

 USSR (3). 



A P 



Fig. 1. Azimuthal arrangement. 



This method has a number of advantages over the vertical electrical prob- 

 ing carried out with the symmetrical four-pole AMNB apparatus. Apart 

 from the possibility of producing deep probings by using small spacings 

 of electrodes (1-2 km) and the improved quality of the measurement? 

 due to decrease in the harmful effect of leaks, the quadrilateral probings 

 have increased resolving capacity with respect to the inchnation of the 

 reflecting electrical horizon. "j" However, under conditions involving swamps 

 and forests, the method of quadrilateral probings, which requires movements 

 over long straight routes, is of limited application. 



In this respect, much better possibilities are shown by the method of 

 two-way probings with an azimuthal arrangement (Fig. 1), a special case of 



* The word equatorial is used in Russian, which however would be misleading in English. 

 [Editor's footnote]. 



t Electrically reflecting horizon is a horizon of high resistance. This translation is necessary 

 since the same term is used by the Russian geophysicists for a seismically reflecting horizon. 



