Transform fault(red)
A
transform fault or
transform boundary, also known as
conservative plate boundary, is a
fault which runs along the boundary of a
tectonic plate. The relative
motion of such plates is
horizontal in either
sinistral or
dextral direction. Typically, some vertical motion may also exist, but the principal vectors in a transform fault are oriented horizontally. Not all faults are transform faults, and not all plate boundaries are transform faults.
Most transform faults are found on the ocean floor, where they often offset active
spreading ridges to form a zigzag plate boundary. However, the best-known transform faults are found on land.
Transform faults are one of the three types of plate boundaries in
plate tectonics. Transform faults occur where plates slide past each other, and crust is neither destroyed nor created.
Divergent faults occur where magma seeps up through the earth's crust, and new crust is formed as the plates are pushed away from each other.
Convergent faults occur where two plates collide and one plate is forced under the other plate (in a process known as
subduction or
obduction), and as a consequence, the plate being forced under is melted and destroyed. When two continental plates converge, they may push up against each other (in a process known as
continental collision) forming mountain ranges, however, subduction may still occur. Plate tectonics was proposed by
J. Tuzo Wilson in 1965 and he particularly recognized the concept in the case of the transverse strike-slip faults along which
mid-oceanic ridges are off-set.
Mechanics
The left- or right-lateral motion of one plate against another along transform faults can cause highly visible seismic lithosphereic crust effects. Because of
friction, the plates cannot simply glide past each other. Rather,
stress builds up in both plates and when it reaches a level that exceeds the strain threshold of rocks on either side of the fault the accumulated
potential energy is released as
strain. Strain is both cumulative and instantaneous depending on the
rheology of the rock; the ductile lower crust and mantle accumulates deformation gradually via
shearing whereas the brittle upper crust reacts by fracture, or instantaneous stress release to cause motion along the fault. The ductile surface of the fault can also release instantaneously when the strain rate is too great. The energy released by instantaneous strain release is the cause of
earthquakes, a common phenomenon along transform boundaries.
Examples
The
San Andreas fault in
California is a major transform fault which runs between the
Mendocino Triple Junction in the north and the northern end of the
East Pacific Rise somewhere beneath the
Imperial Valley in the south.
Other examples include:
See also
