Plate Boundary

A plate boundary is the contact between two lithospheric plates, where nearly all earthquakes, volcanism, and crustal deformation concentrate. Three kinds exist: divergent, where plates pull apart and new crust forms at mid-ocean ridges; convergent, where plates collide and one subducts at an ocean trench, building island arcs and volcanic arcs; and transform, where plates slide past one another along strike-slip faults such as the ridge-offsetting transform faults of the seafloor. Relative motion runs from about 1 cm/yr at slow boundaries to over 15 cm/yr at the fast East Pacific Rise. The global belt of boundaries traces the seismic Ring of Fire around the Pacific.