Geology Reference
In-Depth Information
11.6.2
Fault Shape Prediction
Based on the assumption of constant BLT on a cross section bounded by vertical pin
lines, there is a unique relationship between the hangingwall shape caused by move-
ment on a fault and the shape of the fault itself. In the technique developed by Geiser
et al. (1988), a complete deformed-state cross section is constructed while simulta-
neously producing a restored cross section. The method is based on: (1) constant bed
length and bed thickness, (2) slip parallel to bedding, (3) fixed pin lines in the hanging-
wall and footwall of the fault, and (4) the hangingwall geometry is controlled by the
fault shape. The pin lines are chosen to be perpendicular to bedding. The data re-
quired to use the method are the location of a reference bed and the hangingwall and
footwall fault cutoff locations of the reference bed. The original regional of the refer-
ence surface is not required. The method produces a cross section that is length bal-
anced, has constant bed thickness and has bedding-normal pin lines at both ends.
The technique is as follows:
1. Define the reference bed, its fault cutoffs, and the shape of the fault between the
cutoffs (Fig. 11.36a, top).
2. Place the pin lines in the deformed-state cross section. Usually they are chosen to
be perpendicular to bedding and beyond the limits of the structure of interest
(Fig. 11.36a, top).
3. Measure the bed length of the reference horizon between the pin lines and draw the
restored-state section (Fig. 11.36a, bottom).
4. Construct one or more constant thickness beds in the hangingwall between the
hangingwall pin and the fault (Fig. 11.36b, top).
Fig. 11.36.
Construction of fault shape from a hangingwall bed based on the constant BLT assumption
(Geiser et al. 1988).
a
Initial geometry.
b
After first cycle of construction, hangingwall is restored.
c
After
the first cycle of hangingwall restoration, the footwall is restored.
d
Completed cross section
