Geology Reference
In-Depth Information
Fig. 8.26.
Interpreted isopach map of the
top of the lower Taylor Forma-
tion on part of the Hawkins
salt dome, Texas. The contour
interval is 50 ft.
D
Downthrown
block,
U
upthrown block. (Iso-
pach map after Hintze 1971)
A map on a portion of a salt dome provides an example of the effect of normal faults
on an isopach map. Elongate zones of isopach thinning are developed along faults
(Fig. 8.26). On a traverse across the north-south fault, the throw is 150 ft on the east
(Eq. 8.4: 400-250) and 200 ft (Eq. 8.4: 450-250) on the west. The thicker section on the
west of the normal fault indicates that it dips to the west. A similar analysis indicates
that the east-west fault is a growth fault, down to the south with 150 ft of throw at the
top of the unit and 200 ft at its base.
8.6
Displacement Transfer
This section describes the geometry of linked faults. As a fault dies out it usually trans-
fers its displacement to another fault (Fig. 8.27). Displacement transfer between nearby
faults is an important process in both map and cross section (Crowell 1974; Childs
et al. 1995; Walsh et al. 1999). Faults that transfer displacement but do not intersect are
termed soft linked and are separated by a continuous bed segment called a relay ramp
(Kelly 1979). Faults that intersect are said to be hard linked (Walsh and Watterson 1991;
Childs et al. 1993) and join along a branch line (Boyer and Elliott 1982). Conjugate
faults (Sect. 1.6.4) that overlap will form convergent or divergent links (Fig. 8.27). Bends
or overlaps that trend oblique to the slip direction are either restraining or releasing
(Crowell 1974; Mansfield and Cartwright 1996) depending on their overlap direction
relative to the slip direction (Fig. 8.28).
