Chap. 10] ELECTRICAL METHODS 



which gives for the apparent resistivity 



1 



p. = Pi 



1 +2k 



721 



(10-41b) 



Tagg'" has published a series of curves showing for various k values the 

 apparent resistivity as a function of distance from the contact. These 



fi>A 



Fig. 10-56a. Apparent conductivities obtained with four-terminal electrode 

 arrangements on contact (after Tagg). 



4 3 2 10 12 3 4 



a 



Fig. 10-566. Apparent resistivities obtained with four-terminal electrode arrange- 

 ments on contact, as a function of distance of center of spread from contact plane 

 (in terms of electrode separation) (after Tagg) = 



indicate that if the distance of the electrode system from the fault is four 

 times the electrode separation, its influence is practically negligible. 

 5. Effects of dipping beds. For dipping beds, apparent resistivities may 



"G. F. Tagg, A.LM.E. Geophys. Pros., 135-145 (1934). 



