Transform fault

Transformative faults (red lines).

An edge or transform fault is a fault that moves laterally from one tectonic plate relative to the other. Its presence is detected thanks to the geological discontinuities of the terrain.

There are two types of transform fault: those that segment the mid-oceanic ridges and those that form the passive boundaries between continental tectonic plates.

At the faults or transform edges that form the passive boundaries between tectonic plates, the plates move past each other horizontally, without producing or destroying lithosphere. The best known transform fault of this type is the San Andreas fault in California (USA).

Those that occur at the constructive edges of plates are those that divide the mid-oceanic ridges into more or less short segments with a straight line, to accommodate them to a general curved or sinuous or oblique path with respect to the direction of expansion of the ocean floor (see image to the right).

The other two types of tectonic plate edges, convergent edges and divergent edges, are tectonically active and both have associated volcanic activity:

A convergent edge is where tectonic plates collide and, depending on the type of crust involved (oceanic-oceanic, oceanic-continental, or continental-continental), subduction occurs and the formation of island arcs or orogenies (creation of relief and formation of of new continental crust).

At a divergent edge, tectonic plates move apart, causing material to rise from the mantle and create new ocean floor, or new ocean crust.