Geology Reference
In-Depth Information
Fig. 11.46.
Restoration by oblique simple
shear.
Medium-weight solid
lines
are marker beds.
Dotted
lines
represent the shear direc-
tion and are spaced an arbi-
trary distance
S
apart. The
widest lines
are the thicknesses
in the shear direction to be
restored. The shear angle is
α
.
a
Deformed-state cross section.
b
Restored cross section
Fig. 11.47.
Restoration of the hangingwall
of a fault by oblique simple
shear.
FWC:
footwall cutoff of
reference bed;
HWC:
hanging-
wall cutoff of reference bed;
t
i
: distance between reference
bed and fault, measured along
shear direction;
:
shear angle;
D
:
block displacement
α
Note that for oblique simple shear,
D
is not equal to the fault heave on the ramp, but is
equal to the displacement on the lower detachment. The steps in the restoration are
given below (refer to Fig. 11.47 for the geometry).
1. Find the regional.
2. The block displacement is found by projecting a line parallel to the shear angle from
the hangingwall cutoff of the reference bed to the regional. The block displacement
is the distance
D
from the footwall cutoff of the marker bed.
3. Along the regional, mark off equal distances,
D
. Through each point draw a working
line parallel to the shear direction, starting at the footwall cutoff of the reference bed.
4. Mark the position where each bed crosses a working line.
5. Each oblique segment of working line is moved up the fault a horizontal distance equal
and opposite to
D
. Keeping the base of the oblique segment in contact with the fault,
mark the location of the top, which is the restored position of the reference bed. Mark
the restored position of all the other beds along this restored oblique segment.
6. Repeat steps 4 and 5 until the hangingwall is restored.
