Flow, deformation, and transport - Physical Processes in Earth and Environmental Sciences - page 159

(a) (d)

(b)

(c)

Listric faults

Detachment

Fig. 4.97 Fault surface geometry. Faults are fairly flat at surface but at depth may show changes in the dip angle. (a) High-angle faults can have
less steep reaches named flats; (b) low-angle faults can have an oversteepened reach or ramp. (c) Faults can experience a progressive decrease in
dip at depth, ending in a very low angle or horizontal surface or detachment. (d) A stepped listric fault array, Corinth canal, Greece.

coefficient commonly. Secondary imbricate fault sets can
be either synthetic , when they have the same dip sense of
the main fault or antithetic , when they have an opposed
dip direction with respect to the main fault.

authors consider both terms synonymous, a distinction
between thrust and reverse faults has been made on the
basis of the surface angle; the first being low-angle faults
and the second high-angle faults. Strike-slip faults are
those having relative movements along the strike of the
fault surface (Fig. 4.98b), generally they have steep sur-
faces close to 90 4.15.2 Fault classification so the terms hangingwall and footwall

do not apply. There are two kinds of strike-slip faults
depending on the relative shear movement; when an
observer is positioned astride the fault surface, the fault is
right-handed or dextral when the right block comes
toward the observer and is left-handed or sinistral when
the left block does (notice that it does not matter in which
direction the observer is facing; Fig. 4.98). Oblique-slip
faults can be defined by the dip and strike components
derived from the relative movement of the blocks. Four
possible combinations are represented in Fig. 4.98c as
normal-sinistral, normal-dextral, reverse-dextral, and
reverse-sinistral. Finally, rotational faults are those show-
ing displacement gradients along the fault surface; they
are formed when one block rotates with respect to the
other along the fault surface (Fig. 4.98d).

Regarding the relative displacement of blocks along any
fault surface, several kinds of faults can be defined
(Fig. 4.98). Earlier we made a first distinction into
dip-slip, strike-slip, and oblique-slip faults. Dip-slip
faults, having relative block movements parallel to the dip
direction, can be separated into normal faults and reverse
or thrust faults according to the sense of shear
(Fig. 4.98a). Normal faults are generally high-angle
faults, with surfaces dipping close to 60 in which

the hangingwall block slides down the fault surface, as the
down-throw block (Fig. 4.95b). Low-angle normal faults
can also form. Reverse and thrust faults are those in which
the hangingwall block is forced up the fault surface, defin-
ing the up-thrown block (Fig. 4.95a). Although many