Geology Reference
In-Depth Information
Structure Contouring
3.1
Introduction
This chapter covers the basic techniques for contouring continuous surfaces and for
the construction of composite-surface maps. The contouring of faults and faulted sur-
faces is treated in Chap. 7.
3.2
Structure Contouring
A structure contour map is one of the most important tools for three-dimensional
structural interpretation because it represents the full three-dimensional form of a
map horizon. The mapping techniques to be discussed are equally applicable in sur-
face and subsurface interpretation. The usual steps required to produce a structure
contour map are:
1. Plot the points to be mapped.
2. Determine an appropriate contour interval.
3. Interpolate the locations of the contour elevations between the control points. There
are several techniques for doing this and they may give very different results when
only a small amount of data is available.
A structure contour map is constructed from the information at a number of obser-
vation points. The observations may be either the
xyz
positions of points on the sur-
face, the attitude of the surface, or both. A relatively even distribution of points is
desirable and which, in addition, includes the local maximum and minimum values of
the elevation. If the data are from a geologic map or from 2-D seismic-reflection pro-
files, a very large number of closely spaced points may be available along widely spaced
lines that represent the traces of outcrops or seismic lines, with little or no data be-
tween the lines. The number of points in a data set of this type will probably need to
be reduced to make it more interpretable. Even if the contouring is to be done by com-
puter, it is possible to have too much information (Jones et al. 1986). This is because
the first step in contouring is always the identification of the neighboring points in all
directions from a given data point and it is difficult and usually ambiguous to choose
the neighbors between widely spaced lines of closely spaced points. Before contouring,
the lines of data points may need to be resampled on a larger interval that is still small
enough to preserve the form of the surface.
