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.
The San Andreas Fault in California is an example of a transform boundary, where two plates grind past each other along what are called strike-slip faults. These boundaries don't produce spectacular features like mountains or oceans, but the halting motion often triggers large earthquakes, such as the 1906 one that devastated San Francisco.