388 



MAGNETIC METHOD 



[Chap. 8 



where di , pi and dz , pt are the depths and distances respectively to the 

 upper and lower pole lines. 



6. For the inclined line doublet the fields of upper and lower pole series 

 are again superimposed as in eq. (8-54). With x' as horizontal distance 

 and di as depth to the upper pole, the anomalies 



AH = 2C - :^ + 



L p\ 



and 



AZ = 



Lpi 



(8-57) 



#here'2Z is the length (depth extent) of the plate and i its dip. 



Fig. 8-49. Force-line diagram in application (after Haanel). 



7. The magnetic anomalies of irregular geologic features may be calcu- 

 lated by assuming a series of poles near the upper surfaces of such features. 

 If the depth extent is limited, vertical magnets are substituted for the 

 single poles. For two-dimensional features with irregular upper or lower 

 surfaces, magnetized lines along the upper and, if necessary, along the 

 lower boundary should be assumed. The spacing of poles or lines does 

 not have to be very close (particularly when the depth is great), since the 

 magnetic method does not have much resolving power. 



With the pole and line theory, induction effects (variations with mag- 

 netic latitude) may be simulated by placing oblique pole or line doublets 

 into the formation section. Since neither the horizontal nor the vertical 

 intensity anomalies are particularly sensitive to dip, the assumption of 

 oblique magnetization does not afford much advantage except when the 

 magnetic inclination is less than 60°. 



