Tectonic Plates and Faults - Earthquake Engineering for Structural Design - page 165

Hanging wall Foot wall

Figure 5.20 Reverse or thrust faults: (a) Crustal block before faulting; (b) After
faulting; (c) Erosion of reverse fault (modified after Dutch, 1997)

Fracture intensioncrust (Fig. 5.22). If a crust weakness exists, the plume rising
from the mantle, producing tension stresses and fractures in the continental crust.
So, normal fault forms when the crust is stretched, tensioned or pulled apart (Fig.
5.23). After a certain amount of elastic deformation, the tension in crust becomes
too much and brittle fracture must cause a gap between the two crustal blocks. But,
as this gap could never exist in nature, the two blocks must stay in contact across
the fault plane. To do this, in many cases, instead of having just one normal fault, a
whole series of fault plane can occurs, the crust pulls apart, giving rise to a riftfault
(Fig. 5.24), with two parallel normal faults. In this fault, the uplifted segment is
called horst block and the down-dropped segment, graben block . The best
examples of these fault types are the Dead Valley (North America), the Upper
Rhine (Western Europe, Fig. 5.25) and the Lake Baikal (Asia) (the deepest
continental rift on the Earth).