Fracture traces are believed to be the surface expressions of localized bedrock jointing
and small faults (Casper, 1980). Recent studies have indicated that fracture orientations
measured on the surface have similar orientations to those in the subsurface (McGlew and
Thomas, 1984). Fractures may result from local adjustment to regional stress conditions, and
may be the surface expression of minor faults, solution zones, concentrated jointing, or
separation of strata during folding (Casper, 1980).
A fracture trace analysis is performed by examining remote sensing imagery such as
aerial photography for linear and curvilinear features at various scales, which are related to
bedrock fractures. There are many types of imagery available in different scales. The
selection of the proper imagery for a given study area depends on the topography, type of
vegetation, soil moisture content, expected size of surface expression of geologic features,
size of the study area, and numerous other features (Jansen and Taylor, 1988).
Fracture traces are viewed in stereoscopic analysis of aerial photographs. By
systematically viewing small portions of the area, it is possible to locate fracture traces
expressed by continuous or discontinuous tonal variations of surface features (Casper, 1980).