At a transform plate boundary, two tectonic plates pass one another, creating a fracture zone. This motion causes phenomena such as earthquakes.
The outer shell of the earth comprises tectonic, or lithospheric, plates composed of solid rock. When two tectonic plates move alongside each other, they create a fracture zone that produces a transform plate boundary also known as a transform fault. The two other ways that plates can move relative to one another is together, which is called tectonic convergence, or apart, which is called tectonic divergence.
Most transform plate boundaries are in the ocean basin where they connect parts of the mid-ocean ridges, but there are a few significant examples in the continental lithosphere, or on land, the most famous being the San Andreas Fault Zone that divides California. The boundary comprises the Pacific Plate on the west and the North American plate on the east, as stated by the United States Geological Survey. Another example is the Alpine Fault, which follows a path that almost extends the full length of South Island in New Zealand.
Recurring earthquake activity takes place at transform plate boundaries. These earthquakes generally occur within and between plates not involved in sideways and downward movement, so the earthquakes are typically shallow.