394 



MAGNETIC METHOD 



[Chap. 8 



gravity potential, and i the direction of magnetization, 

 the force in the direction s: 



dV 

 ds 



kh dids' 



From eq. (8-60a) 



(8-606) 



and therefore, the horizontal and vertical components. 



AH = 



kh didx 



and 



AZ = T : 



kh dtdz 



(8-60c) 



It follows from this formula that (1) for vertical magnetization (high 

 magnetic latitudes) the horizontal intensity anomaly is proportional to the 

 horizontal gradient of gravity, and the vertical intensity anomaly is propor- 

 tional to the vertical gradient of gravity; and (2) for horizontal magnetization 

 (near magnetic equator) the horizontal intensity anomaly is proportional 

 to horizontal gradient of horizontal gravity component or proportional 

 to the "curvature" value (for two-dimensional bodies, or to the negative 

 vertical gravity gradient), and the vertical intensity anomaly is propor- 

 tional to the horizontal gradient of gravity. For three-dimensional bodies 

 application of formulas (8-60c) leads to equations which are involved and 

 difficult to apply. For two-dimensional bodies these relations remain 

 simple, particularly for extreme cases of dip, dimensions, and magnetic 

 latitudes. 



Resolving the magnetization in eq. (8-606) into a transverse horizontal 

 component (A) and a vertical (C) ; assuming that the strike direction is y 

 and the profile direction (at right angles to the strike) is x] and segre- 

 gating the gravity component dU/di into a horizontal and a vertical 

 component, eq. (8-606) is 



(8-60d) 



If x' and y' are the magnetic north and east directions, y the direction of 

 strike, and a the angle of strike from north over west (angle between 

 — y and x' direction), the transverse horizontal magnetization and the 

 vertical magnetization are A = kHq sin a and C = kZo , where k is the 



