A 'transform fault' is a
fault that is a special case of
strike-slip faulting which terminates abruptly, at both ends, at a major transverse geological feature. Also known as a conservative plate boundary.
Transform faults comprise one of the three types of plate boundaries in
plate tectonics. This term 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 surface 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 accumulative 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.
The
San Andreas fault of southern
California is a large transform fault connecting the
East Pacific Rise off the coast of California with a segment of the ridge in the
Gulf of California.
See also
★
Fault (geology)
★
Fracture zone
★
Plate tectonics
★
Transform boundary
★
Structural geology
References
★ International Tectonic Dictionary - AAPG Memoir 7, 1967
★ The Encyclopedia of Structural Geology and Plate Tectonics - Ed. by Carl K. Seyfert, 1987