A transformation fault or transform fault is a geological fault that occurs when two tectonic plates are slipping along each other in opposite directions. The actual fault is a strike-slip fault. The most well-known example is the San Andreas fault in California (USA).
Along transformation faults earthquakes are numerous but major earthquakes are not as probable as for example on a subduction zone. However, earthquakes on such faults are usually shallow and therefore potentially dangerous. A recent example of such an earthquake was the Haiti earthquake 2010. The vast majority of transformation faults can be observed along oceanic ridges. The ridges are divided into small segments which slip along each other. This makes the typical zig-zag pattern of the actual plate boundary along oceanic ridges. Strike-slip faults are found in those areas where the plate boundary runs parallel to the movement direction of the diverging plates.