Flow, deformation, and transport - Physical Processes in Earth and Environmental Sciences - page 157

(a) (b) (c)

Fig. 4.92 (a) Fault, (b) fault zone, and (c) ductile shear zone. Faults are well-defined surfaces produced by brittle deformation. Weak rocks
can be deformed by brittle deformation giving rise to a fault zone with multiple, closely spaced, sometimes interconnected surfaces. Shear
bands develop in the ductile field.

(a)

(b)

(c)

Fig. 4.93 Faulting is marked by conspicuous shear displacements, forming distinctive features on fault surfaces like (a) bends and grooves
(b) slickenlines. In (c), originally continuous bedding traces seen in vertical section show up fault displacement (all photos taken in central
Greece.

and direction. The relative movement can be either paral-
lel to the fault dip direction ( dip - slip faults ) or to the fault
strike ( strike - slip faults ). Dip-slip faults show vertical dis-
placements of blocks whereas in strike-slip faults the
displacement is hori-zontal. In a composite case, the
movement of blocks can be oblique; in these oblique-slip
faults blocks move diagonally along the fault surface,
allowing the separation of a dip-slip component and a
strike-slip component (Fig. 4.94a). The dip-slip component

can be separated into a horizontal part which is called
heave and a vertical part known as throw (Fig. 4.94b).
When faults show a dip-slip movement the block which is
displaced relatively downward is called down-thrown block
(DTB, Fig. 4.94) and the one displaced relatively upward
up-thrown block (UTB, Fig. 4.95). Blocks in strike-slip
faults are generally referred to according to their orienta-
tion (for instance: north block and south block, etc.). In
most cases accurate deduction of movement vectors is not