284 



V. I. FOMINA 



Basing ourselves on the comparison of calculated and approximately 

 constructed VEP curves for q^ < (^i /c)l ^^'® ^^^ therefore consider that up 

 to the limits of spacings AB used in practice the accuracy of the approxi- 

 mate construction of curves is also fully adequate to enable us to explain 

 relative variations in the form of VEP graphs. 



Curves for perpendicular orientation of the AB for spacings the cases c 



d , . 



and d (Fig. 1) and various values of — are given in Figs. 9 and 5. A satisfac- 



H 



tory value of S may be obtained by analogy with the previous cases from 

 the first asymptote of the VEP curves when d > 2H. 



For d < 2H up to <i = \H, values of S obtained from the final branch 

 of the curve will be increased in relation to their true value by anything 

 from 15-30%. For d <.^j^H lh.e values of S obtained will fall within the 

 limits of accuracy of the observations. 



Here, as in the case of a vertical contact for {q^ j^j^ <C Q^-, the abscissa of 

 maximum deviation of q^^ is equal to d. The position of the vertical contact 

 may therefore be obtained and the depth at which the reference horizon 

 lies be estimated by profiling the abscissae of the maximum deviation of 



1-0 



-y^ 



v; 



-■;l- >...>'. 



y:^T^ 



\' 



\ 



\ 



V V 







AB 

 26 



Fig. 10. a — VEP curves for a horizontal homogeneous medium; b — approximately 

 constructed VEP curves; c — curves of the CV-2S reference graph. 



