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Figure 8.10 (a) Examples of orientated 'thumbnail' sketches of kinematic indicators from a fi eld notebook.
(b) An orientated sketch of structural features in a larger exposure. (Notebook of Tom W. Argles, The Open
University, UK.)
For many kinematic indicators, a simple fi eld sketch is an
adequate record. Photographs are also useful, but sketches
(Figure 8.10) can incorporate a level of interpretation that is
lacking in a photograph. For any structural sketch or
photograph, it is essential to specify:
1. orientation, using compass directions (e.g. 'Photograph
looking SW', or SE-NW at either end of sketch);
2. the attitude of the surface depicted (e.g. subvertical cliff,
gently-dipping slab).
For some features (e.g. Riedel fractures, gouge fabrics),
measurements can provide more information, for instance the
orientation of the overall fault zone, if this is obscure (Worked
Example 8.1, pp. 174-175).
Without a visible piercing point, the actual magnitude of slip
on a fault can rarely be determined in the fi eld, because visible
offsets can result from a range of fault displacements (Figure
8.7, p. 171). Juxtaposed beds in a well-documented stratigraphic
section may allow you to determine the minimum throw
(vertical displacement; Figure 8.14, p. 176) of the fault, which
for dip-slip faults is a useful fi rst-order comparison (major
faults have large throws). Few fault planes are exposed enough
to enable addition of incremental fault slip steps (Figure 8.6c,
p. 170), or slickenfi bre lengths (e.g. Figure 8.6b). Since the
fi bres generally record only a part of the motion history,
measurement of the longest fi bres observed will give at best a
minimum estimate.
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