GRAVITATIONAL METHODS 



345 



* is the angle which the R-Hne makes with the profile Hne. An example 

 of a curvature quantity profile is given in Figure 197 for the anticline shown 

 in Figure 196. 





y 



(b) 



PROFILE 





^7- 



(a) PLAN VIEW 



-7^ 



LIGHT MATERIAL 



Fig. 196. — Traverse of torsion balance stations across a symmetrical 

 anticline, (a) Plan view of gradient and curvature values at stations, 

 (b) Profile of gradient of gravity. 



Note: In (a) the stations are plotted on a curved traverse to per- 

 mit showing their relative gradient lengths without overlapping. Actually, 

 the stations lie along a straight line traverse. 



A special form of projection is necessary, since where the curvatures 

 of equipotential surfaces change from plus to minus from over an anti- 

 cline to the neighboring syncline the direction of the R-line changes by 

 90°. A simple projection onto a profile line would not show such a 

 variation. 



The values of the quantities plotted in the profile of Figure 197 are 

 presented in Table 9. The table shows that the sign of the ordinate is 

 considered as negative where the stations are above the top of the structure 

 (anticlinal form of gravity equipotential surfaces). The sign is positive 

 where the stations are under the influence of synclinal conditions. Figure 

 197 is plotted on this basis, and shows that the sign of the curvature 

 quantity changes between those stations where the direction of the R-line 

 changes by 90°. As is expected, the maximum value of the curvature 

 quantity is over the crest of the structure. 



