Fold Geometry - 3-D Structural Geology - page 113

The new coordinates than can plotted as an xy graph and will have the geometry of
a tangent diagram. The best-fit curve through the data can be found with standard
curve-fitting routines. Experience using simple spreadsheet curve-fitting functions
indicates that when a quadratic curve produces a smooth hyperbolic-like shape (eg.,
Fig. 5.8b), it is an appropriate fit to the data. If a quadratic curve is irregular, then a
straight-line best fit is more appropriate.
5.2.4
Example Using a Tangent Diagram
Attitude data from a traverse across the central part of the Sequatchie anticline
(Fig. 5.8a) compiled in Table 5.1 provides an example of fold-axis determination using
Fig. 5.8. Fold geometry of a portion of the Sequatchie anticline. a Index map to location of attitude data
( rectangle ) on structure-contour map. Squares represent measurement locations. b Tangent diagram
for data within rectangle, showing best-fit curve through the data and the axis trend
Table 5.1.
Bedding attitudes across the
central Sequatchie anticline
from NW to SE