Most of the earthquakes in North America occur along its tectonically active western margin. That margin includes three different subduction zones, where oceanic lithosphere descends beneath the North American plate to feed volcanoes of the Aleutian arc, the Cascades Range, and the Mexican and Central American volcanic belts. The Pacific plate also grinds NW against the North American plate along the San Andreas fault. The boundary between these two plates is actually distributed over a broad zone that extends more than a thousand km inland. Infrequent but powerful earthquakes can also occur in midwestern and eastern states. The August 31, 1886 earthquake in Charleston, S.C., was one of the largest in U.S. history.
