A subduction zone is formed at a convergent plate boundary when one or both of the tectonic plates is composed of oceanic crust. The denser plate, made of oceanic crust, is subducted underneath the less dense plate, which can be either continental or oceanic crust.hen one plate is composed of oceanic lithosphere and the other is composed of continental lithosphere, the denser oceanic plate is subducted, often forming an orogenic belt and associated mountain range. This type of convergent boundary is similar to the Andes or the Cascade Range in North America.
The San Andreas fault is one of only a few examples of a transform boundary between two tectonic plates that is exposed on a continent. Some other continental transforms are the Alpine fault in New Zealand and the Dead Sea Transform fault system in the Middle East.he remainder is expressed by displacement along other, subparallel faults such as the Imperial and the San Jacinto fault zones in southern California. The San Andreas fault zone is a transform boundary between two tectonic plates, the North America plate and the Pacific plate.
Because of its horizontal direction of movement, the San Andreas fault is categorized as a transform or strike-slip fault. Other faults are categorized by vertical movement. If the vertical movement is downward, the fault is categorized as a normal fault. Vertical movement upward creates a reverse fault.