Amateur geologists often assume that the continental and oceanic plates coincide with the observable physical geography. In fact, most of the tectonic plates harbor both land and sea areas, which are merely surface features on the thick, underlying plates. For example, there is no Atlantic Plate; rather, this ocean is opening along the mid Atlantic Ridge and the crust formed on either side becomes part of the bordering Continental plates (i.e. this ridge is a rift between the North American and Eurasian Plates and between the South American and African Plates).
Land associated with a particular Continent does not always lie on that Continental Plate. The North American Plate, for example, stretches from the middle of the North Atlantic to the Pacific Coast; however, its northwestern extension runs across the northern edge of the Pacific Ocean, taking in the Aleutians, the Bering Sea, the northern islands of Japan and the eastern portion of Siberia. On the other hand, Southern California lies on the Pacific Plate but will eventually join the North American Plate after a long journey to Alaska. India, part of Asia on the map, actually sits on its own plate and Australia's plate runs beneath most of the Indian Ocean, a swath of the Southern Ocean, the eastern islands of Indonesia and both the Coral and Tasman Seas.
Since most earthquakes and volcanoes are associated with friction, compression and subduction along plate margins, it is important to know where these margins are located. More often than not, they do not correspond with what we see on the map!
