THE LOOP METHOD IN EXPLORING BURIED STRUCTURES 263 



for AB < 400 m is the e.m.f. received, corresponding to the final stage 

 of stabihzation of the electromagnetic field in the earth. 



With further increase in AB, the intervals of the observations referred 

 to the initial stage of stabilizing, i.e. the measured e.m.f.s characterized 

 only the upper deposits of the section. 



Calculation showed the possibility for receiving e.m.f.s corresponding 

 to the final stage of field stabilization for any values of AB and other fixed 

 observational conditions by means of the corresponding change in the 

 pulsator collector. 



Observations with the frame receiving frame circuit are worthy of atten- 

 tion and are of practical interest. 



The e.m.f. induced in the receiving frame for each of the two mutually 

 perpendicular positions of the AB line, fed by a low frequency alternating 

 current, are compensated by inclining the frame or can be measured by an 

 appropriate measuring apparatus. 



The two -component vectors of the loop obtained in this way make it 

 possible to construct a vector at each observation point oriented in the 

 direction of preferential propagation of the current, i.e. along the dip of the 

 rocks. The field of the loop method vectors should characterize the tecto- 

 nics of the studied deposits to a depth corresponding to the depth of 

 penetration of the magnetic field of a given frequency for a known value 

 oiAB. 



The observations made with a receiving frame circuit even under complex 

 physico -geological conditions, always led to results agreeing with the geologi- 

 cal data. 



A number of problems arising during the trials on the modernization of the 

 loop method could not be solved due to the low technical level on which they 

 were carried out in 1953. However, this work established the possibility 

 of such a modernization and indicated the future course of development. 



From this brief review of work carried out by the loop method it can be 

 seen that under favourable physico -geological conditions, the results of the 

 method are not only supported by geological surveying but in a number of 

 cases they add to it and correct it(^^» ^^' ^^K 



For example, by comparing the character of the field of loop vectors for 

 a number of areas in the Kerch peninsula with the seismic results and elec- 

 tric logging of wells, drilled in these areas, it can be concluded that the 

 structure of the upper 40-50 m of the section (observations by the loop 

 method were carried out mainly with d = 100 m, AB = 200 m) reflects 

 the structure down to a depth of about 500 m. Consequently, in this region 

 the results of surveying by the loop method can orientate the cartographic 



