Geology Reference
In-Depth Information
Fig. 9.24.
Determination of
T
and
L
di-
rections for data in Table 9.2.
a
Tangent diagram.
b
Dip-
azimuth diagram
The final part of the interpretation is based on the
T
and
L
component plots. A
normal fault dips in the direction the cusp points on a
T
component plot, which is to
the southwest for this example (Fig. 9.25a). At this stage, the effect of the choice of the
T
and
L
directions on the component plots should be examined. Vary their directions
and watch for the effect on the
L
-component plot. The best result is one which shows
the points falling the closest to the zero line, indicating that the
L
direction has been
correctly chosen. The result in Fig. 9.25b is the best that can be obtained from this data
set. Note that the data point that was at the tip of the cusp on the dip-depth plot
(Fig. 9.23b) lies on the wrong (NE) side of the
T
-component plot (Fig. 9.25a). Re-ex-
amination of the original data (Fig. 9.22) shows this to be a point with poor data qual-
ity. It might represent a dip on a fracture or be a spurious result on fractured rock in
the fault zone. No data at all might be expected from a fault zone in which the bedding
has been highly disrupted by the deformation.
