Geology Reference
In-Depth Information
7.5
Geometric Properties of Faults
In this section the typical characteristics of an individual fault surface and its displace-
ment distribution are described.
7.5.1
Surface Shape
A fault surface is usually planar to smoothly curved or gently undulating (Fig. 7.21).
The structure contour map of a fault surface should usually be smooth. Viewed over
their entire surface, many faults are smoothly curved into a spoon-like shape. Primary
surface undulations, if present, are typically aligned in the slip direction and provide
a good criterion for the slip direction (Thibaut et al. 1996).
7.5.2
Displacement Distribution
The displacement on a fault dies out at a tip line which is the trace in space of the
terminations of a fault (Boyer and Elliott 1982). If the displacement dies out in all di-
rections (Barnett et al. 1987), the fault is surrounded by a tip line (Fig. 7.22) like a dis-
location in the theory of crystal plasticity (Nicolas and Poirier 1976). Faults are typi-
cally significantly longer in the strike direction than in the dip direction. Faults always
Fig. 7.21.
Perspective block diagram of a
curved fault surface
Fig. 7.22.
Dislocation-like fault for which
the displacement (
arrow
) dies
out to zero in all directions at
the tip line. The trace of the
displaced marker horizon is
dashed
on the footwall of the
fault and
solid
on the hanging-
wall
