Strike
slip
faults
accommodate
horizontal
displacement, are roughly
vertical with straight to gently
curved surface traces, and
result in no to little net change
in crust surface area. These
faults produce a large number
of characteristic surface and
subsurface features including
surface
feature
offsets,
fracturing, folding, etc.
Transform faults are major regional
strike slip fault systems that form
segments of lithospheric plate boundaries.
Transcurrent faults are major regional
scale strike slip faults are found within
continental crusts, away from plate
margins. Tear faults are small-scale,
steeply dipping local strike slip faults
subsidiary to larger structures (folding,
normal, or thrust faulting) found in the
hanging wall block with displacement
subparallel to regional direction of
displacement. They help accommodate
differences in displacement on either side
of the fault.
Characteristic of Strike Slip Faults:

Subhorizontal
slickenside
lineations (see ch 3)

Linear erosion depressions

Springs

Pull apart basins (caused by
displacement at extensional
bends and stepovers)

Sag ponds (water filled pull apart
basins)

Offset streams and topography
(including shutter ridges-where
topographic valleys are in front
of topographic ridges)

Small amounts of normal and/or
thrust faulting, drag folds

Subsidiary
shear
fractures;
Ridel/R shears (synthetic to main
fault at a roughly 10-20 angle
with the same shear sense), P
shears (synthetic to main fault,
oriented
symmetrically
in
respects to fault and Rshears), R’
shears (antithetic to main fault at
angles of roughly 70-80, with a
opposite shear sense to fault),
and Y shears (synthetic and
parallel to main fault).
Associated Structures:
1. Folds and Thrust faults form en
echelon along or at the tips of the main
strike slip fault. The trend of the fold
hinge, or strike of thrust in generally 135
or more from the fault measured in the
direction of shear sense.
They
accommodate compression along the
fault.
2. Normal faults form en echelon
along the main fault. They are found at
about 45 to the main fault measured in
the direction of shear sense. They
accommodate extension along the fault.
3. Bends (aka jogs) are curved
portions of a strike slip fault that connect
two roughly parallel sections of the fault.
Stepovers (aka offsteps) are regions
where one fault section ends and another
en echelon fault with the same orientation
begins. Bends and stepovers can be
described
as
being
Contractional/Restraining if the main
fault is pushing material together, or
Extensional/Releasing/Dilatant if the
main fault is pulling material apart.
4. Strike Slip Duplexes are sets of
horizontally stacked horses bounded on
both sides by segments of the main fault,
caused by the presence of bends or
stepovers. These duplexes differ from
duplexes on dip slip faults because of the
different orientations of shear planes.
Vertical
displacement
caused
by
thickening or thinning of the crust must be
accommodated by oblique motion which
creates a collection of strike-slip and
normal slip faults collectively known as a
duplex. In cross section these duplexes
have a flower structure. A normal dipslip
movement will result in a negative flower,
or tulip structure. A reverse dipslip
1
movement will result in a positive flower,
or palm tree structure. Scissor faults can
be found in duplexes, and accommodate
rotation of horse blocks.
Terminations:
At depth strike slip faults either
1. End in another fault , generally at a
much lower angle, or
ß2. Continue down into the crust and
lose identity at depth where they
encounter zones of more ductile
deformation. This is supported by the fact
that earthquakes associated with strike
slip faults only occur up to depths of 1520km.
At the surface strike slip faults
terminate in zones of either extension or
contraction. These faults splay and turn
into imbricate fans of either normal faults
(in the case of an extensional
environment) or thrust faults (in the case
of a compression environment). In some
cases the fault can also break into a
horsetail splay (a fan of strike slip splays).
These will curve towards the receding
fault block.
References & Resources
Robert J. Twiss, Eldridge M. Moores,
Structural Geology 2nd edition, (W. H.
Freeman), p. 135-150, 2006
Meredith Goebel, 2011
Revised by Esther Adelstein and
Michael Chamberlain, 2013