214 



EXPLORATION GEOPHYSICS 



Calculation and construction of these curves are useful tools in interpre- 

 tation. This procedure is valid only to the extent that the geologic condi- 

 tions or the shape of the magnetic ore body permit such simplification. 



Magnetic Disturbance Vectors. — Where both vertical and horizontal 

 intensity measurements have been taken along a traverse crossing a magnetic 

 feature which can be treated as a pole, it is possible to plot the disturbance 



I AZ • 4 



Fig. 101. — Magnetic disturbance vectors for pole depth determination. 



vectors. The procedure is as follows : After subtracting the local average 

 of Z and of H from the field observations, the curves of AZ and A// are 

 plotted in a graph, the spacing of the stations being shown to proper scale, 

 as abscissae. (See Figure 101.) On a line parallel to and below the line 

 of abscissae the stations are plotted. 



At a station on the lower x axis of the figure, the amount of AZ for 

 that station is plotted downward, using some convenient scale. The amount 

 of the AH for the station is plotted at the same scale, to the left if the AH is 

 negative and to the right where the AH value is positive. The AH is plotted. 



