294 V.I. FoMiNA 



within the limits of the measurement interval. The positions of the dipoles MN 

 have been plotted in pairs over the profile for the maximum and minimum 

 deviations of Qj^. DQP curves No. +32; +27; +30 are typical examples 

 of distortions of this type. The sharp deviations in the magnitudes of q^^ which 

 are obtained are (as is obvious from the vertical cross section given in Fig. 16) 

 brought about by the non -horizontal boundaries in the uppermost part of 

 the cross -section (they may possibly be revealed in the diurnal surface)*. 



When the position of the surface non -horizontal boundaries has been 

 established (from analysis of the DQP curves), these distortions can 

 be removed from the DQP curves, as is shown in Figs. 16 and 17. Areas 

 in which Qj^ is increased on account of the buried contact can then be 

 isolated. 



An anomalous region of increase in ^^ (on the minus branches of the 

 DQP) will correspond to an anomalous region of decrease in Qj^ (on the 

 plus branches of the DQP) in the vertical cross-section. Sections in which Qj^ 

 is increased are indicated on DQP curves No. —35; —36; —37 (Fig. 17). 



An anomalous region of decrease in Qj^ is also to be observed in the left-hand 

 part of the profile from the minus branches of the DQP. This decrease is 

 to be seen quite clearly in DQP curve No. —32 (Fig. 17) while on DQP 

 curve No. —26 it is complicated by surface distortions. On the plus DQP 

 given above the profile a region of increase in Qj^ should correspond to this 

 region of decrease in Qj^. A region of this type (left-hand side of the upper 

 profile) cannot be isolated out from the ohm isoline configuration, as was 

 possible in the previous case; it merges with a region of high values in q^^ 

 which correspond to the high resistivity horizon of a layered medium in 

 a raised block. 



An anomalous increase in Qj^ due to the influence of a western non -horizontal 

 contact is, however, revealed with sufficient clarity on the DQP curves and 

 may be isolated by joining the abscissae of the maximum deviation of Qj^ 

 in the DQP along the profile (Fig. 17, DQP curve No. +30). 



There is no justification for ascribing the increases in Qj^ in this instance 

 to surface distortions, since deviations in ^^ on the side of decrease are 

 possible from the nature of the behaviour of the ohm isolines in the upper 

 part of the cross -section. 



Having thus isolated distortions in the magnitudes of Qj^ due to buried 

 non -horizontal boundaries, it is possible to establish the position of the 

 latter as the mean the lines of maxima and minima. In the DQP profile 

 which we have examined, the position of the eastern non-horizontal boundary 



* In what follows these distortions will be called surface distortions. 



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