Geology Reference
In-Depth Information
Fig. 6.14.
3-D map of coal-cycle tops and normal faults in the SE Deerlick Creek coalbed methane field,
Black Warrior Basin, Alabama.
Vertical black lines
are wells (data from Groshong et al. 2003b).
a
Oblique
view to the NW.
Wide line
crossing the region is the slice line.
b
Vertical slice from SW (
left
) to NE
(
right
) across the area
6.4
Predictive Cross-Section Construction
A predictive cross section uses a set of geometric rules to predict the geometry between
scattered control points. This process requires interpolation between data points and
perhaps extrapolation beyond the data points. The best method depends on the nature of
the bed curvature and on the nature of the bed thickness variations, or the lack of bed
thickness variations. Where closely spaced control points are available, any method of
interpolation will produce similar results. Where the data are sparse, the model that
best fits the structural style will provide the basis for drawing the best cross section.
Two predictive methods will be presented here. The first method, here termed the
dip-domain technique, is based on the assumption that the beds occur in planar seg-
ments separated by narrow hinges or faults (Coates 1945; Gill 1953). Easily done by
hand, this method is also widely used in computer-aided structural design programs
and in structural models. The second method is the method of circular arcs, which is
based on the assumption that the beds maintain constant thickness and form segments
of circular arcs (Hewett 1920; Busk 1929). Most cross sections published before the
1950s use this method.
