Geology Reference
In-Depth Information
die out along strike (Figs. 7.22, 7.23a) or transfer displacement to some other fault or
to a fold. Displacement in the dip direction may or may not go to zero. A fault may
flatten into a detachment without losing displacement (Fig. 7.23b; Gibbs 1989). The
variation in displacement in the dip direction is a function of the structural style and
a variety of relationships are possible.
An accurately mapped example from the Westphalian coal measures in the United
Kingdom (Fig. 7.24a) has a displacement distribution nearly as simple as that in Fig. 7.22.
The fault-displacement maps are derived from mapping at five different levels in un-
derground coal mines and so require little inference. Another example from the same
area (Fig. 7.24b) is more complex but the displacement is still seen to die out along
strike. For this area, a representative aspect ratio is 2.15 (strike length/dip length) for
a group of isolated normal faults that die out in all directions for over a length range
of 10 m to 10 km, and is in the range of 0.5 to 8.4 for normal faults that intersect other
faults or reach the surface (Nicol et al. 1996).
Fig. 7.23.
Faults for which the displacement does not die out in the dip direction. The displacement
(
arrow
) dies out along strike at the tip lines marked by
heavy lines
. The trace of the displaced marker
horizon is
dashed
on the footwall of the fault and
solid
on the hangingwall.
a
Fault of unspecified extent
in the dip direction.
b
Fault that bends into a planar lower detachment without losing displacement
Fig. 7.24.
Two examples of contours of
fault throw on normal faults
dipping about 65°. Contours
are projected onto a vertical
plane that has the strike of
the fault. Scales in meters.
a
Elliptical heave distribution.
The fault ends to the right
against the boundary fault.
b
Complex heave distribution.
(After Rippon 1985)
