Chapter 10 



THE USE OF THE LOOP METHOD (SPIR) IN EXPLORING 

 BURIED STRUCTURES 



I. I. Krolenko 



The loop method refers to a group of inductive methods of electrical sur- 

 veying. The first work with this method was carried out in 1930-1932 on 

 the Grozneft regions (by V. N. Dakhnov and then by S. G. Morozov 

 and I. G. Didura). This work was experimental and showed the possibili- 

 ties of the method and the optimum conditions for using it (^^^ 



From 1937 to 1941 and from 1945 to 1950, work with the loop method was 

 conducted on the Kerch peninsula (I. I. Krolenko), where the physico- 

 geological conditions favoured its extensive use. 



As a result of this work and the improvements made in 1947 in the tech- 

 niques of field observations, the loop method became an effective, widely re- 

 producible and relatively cheap method. The method was used to study 

 the tectonics of the upper levels of the geological section. 



Apart from the work on the Kerch peninsula, the loop method was success- 

 fully used on the Caspian shore to the south of Makhach-Kala (1942), on 

 Taman' (1950-1951), in the Turkmenia (1941-1943 and 1952-1953), and 

 was also tried under the conditions prevalent in Western Siberia (1954-1955) 

 and Ust-Urta (1955). 



In the present article we will consider the basic principles of the method 

 and will not deal with the physical nature and the mathematic basis of the 

 loop method, which are given by Dakhnov (^'^°^ who worked out the 

 theory of this method, and also in the papers of A. I. Zaborovskii, E. N. 

 Kalenov, et al. 



The loop method is based on the good electrical conductivity of aniso- 

 tropic (banded) deposits along the layers in comparison with the direction 

 normal to the layer. 



This phenomenon in the case of dipping anisotropic deposits causes an 

 asymmetric magnetic field of the earthed feed loop AB, which for variable 

 fields can easily be set up by means of a closed receiving loop, placed sym- 

 metrically with respect to AB. 



The e.m.f. values arising in the receiving loop are functions of the 



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Applied geophysics 16 



