280 V. I. FoMiNA 



When interpreting the distorted VEP by using parameters of the conduct- 

 ing horizon the deviation in the ordinate of the minimum and the value 

 of S already noted may considerably influence the accuracy with which the 

 depth at which the electrically reflecting horizon lies can be determined. 

 In this case the influence of the vertical contact may lead to a fictitious rise 

 in the reflecting horizon, the axis of the rise being situated at a distance d 

 from the vertical contact. 



Calculation of the influence of the contact is facilitated if cross VEP are 



made with spacings parallel and vertical to the contact. Such investigations 



give us two curves J_ VEP and VEP. The approximately constructed 



d 

 cross VEP curves for various values of — are compared in Fig. 6. 



This comparison yields the following diagnostic features for the curves 

 when Q2^ Qi- 



(1) The magnitude of S (determined from the VEP curve 11 for c? < 2H) 

 is approximately twice less than the analogous value obtained from the 

 VEP curve JL, and the value obtained from the latter is closer to the true 

 value. 



(2) The abscissa of the sharp maximum increase of Qj^ on the _L VEP 

 curve relative to Qj^ on the j VEP curve is equal to d. 



(3) Both curves intersect to the right of the line d. The abscissa of the 

 point of intersection is approximately equal to 2d. 



Fig. 7 shows VEP curves obtained from a drill hole (Pribel'skaia zone, 

 Alakaevskii sector) near the contact \d = — H\ where the angle of its dip 



exceeds 45°. VEP Nos. 67 and 324 were carried out with the spacings of 

 AB respectively orientated parallel and perpendicular to the contact. 



The approximately constructed ±VEP and 1] VEP curves for case 1, a( when 



d l\ 



— = — I are introduced in the lower part of Fig. 7. Comparison shows that 

 H 5 / 



the left-hand branches of these curves and the other curves are the same 

 in type. A certain diflerence is to be observed in the form of the initial bran- 

 ches of the VEP curves and this is, no doubt, caused in the upper part by 

 the complex geological cross section. The characteristic differences between 

 _L and || VEP curves are revealed with sufficient clarity here, and this 

 enables one to establish values of d and S {d =^ 23 m, S = Qm). 



We shall now clarify the nature of the distortions brought about by the 

 influence of the vertical contact when the cross VEP are arranged over 



