Flow, deformation, and transport - Physical Processes in Earth and Environmental Sciences - page 181

Stretching

Shortening

Fig. 4.125 Flexural shear folding.

Class 1C

Class 2

Class 1C

Class 1B

Class 2

Class 1A

Fig. 4.126 Homogenous flattening of previously folded layers.

ability to resist. This commonplace exceedance of the elas-
tic limit (Section 3.15) is a feature of the brittle behavior
of rock as it stretches, expands, compresses, and twists in
response to tectonic and thermodynamic stresses; faults,
folds, and metamorphism (changes of rock state) are the
geological end-result of the cumulative effects of all this
motion (see Sections 4.14- 4.16). Rocks may also be

broken by explosive fragmentation accompanying volcanic
eruptions (Section 5.1). All such rupture processes involve
the release of seismic elastic energy, estimated as an average
total of 7.5 10 17 J annually. Much of the energy is trans-

mitted with the seismic waves that propagate outward
radially from earthquake epicentral zones. A very strong
(and very rarely occurring) earthquake triggered by