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The two diagrams are used to represent the structural pattern or to support the observed pattern. A b diagram is the one on which measured planes are plotted as cyclographic traces, a p diagram is the one on which normals or poles to planes are plotted. Usually for small number of data and involving simple or statistically cylindrical structures or for simple exercises or computations, b diagram is preferred.

For large data and complex deformation patterns the p diagram is preferred. If in the latter case, a b diagram is drawn, it gives rise to non-significant b points since the number of points to be contoured increases too much by N=n(n-1)/2 where N is the intersection points that result from measurements of n number of planes. For example if the number of planes measured is 50, this will plot exactly 50 poles or points on a p diagram easy to contour. But the 50 planes if plotted on a b diagram, would result in 50(50-1)/2, i.e. 1250 points, difficult to contour. b diagrams are generally preferred for analysis of faults, ore shoots, kink-bands and rotational manipulations but for complexly folded terrains, p diagrams are preferred.


Diagrams given to author by M J Fleuty