Geoscience Reference
In-Depth Information
8
Recording structural
information
Tom W. Argles
8
Our planet is an active one, with tectonic plates in constant
motion. Its crust and mantle are subject to changing stresses
that cause rocks to deform, either by breaking or by bending/
stretching (brittle or ductile deformation respectively).
Although we may glean some information on this deformation
from sophisticated seismic methods probing the Earth's depths,
or by measuring infi nitesimal ground motions using satellites,
the most detailed record is preserved in deformed rocks
exposed at the Earth's surface.
Measuring brittle structures provides information on how and
why the upper crust in particular deforms, specifi cally the
orientation of regional and local stresses, and the direction of
motion on faults. Such data help us understand why, how and
where earthquakes occur. Understanding fracture systems is
also critical in exploiting oil, gas, coal and mineral resources
effi ciently; rock structures provide not only challenges, but
also opportunities (such as hydrocarbon traps). Movement of
fl uids through the upper crust is strongly infl uenced by
fractures, so structural geology plays a crucial role in a wide
range of related fi elds, including groundwater studies, pollution
control, geothermal schemes and carbon dioxide storage and
sequestration. Major engineering schemes (e.g. reservoir dams,
barrages, motorways, tunnels) are literally founded on
structural geology. Section 8.2 illustrates some important brittle
structures, to help you recognize them, measure them and
interpret the resulting data.
Ductile deformation dominates strain deep in the crust and in
the mantle, so measurement of ductile structures provides
information on fault motions and stress orientations at
depth, giving insights into regional deformation patterns.
Section 8.3 illustrates some of the commoner ductile
structures.
