Lithospheric plates collide at collision margins, producing fractures in rocks called faults. A fault is a fracture in crustal rock involving the displacement of rock on one side of the fracture with respect to rock on the other side. Like volcanoes, certain faults are active where as others are no longer subject to stress. When rock strata are subjected to stress, they begin to deform or bend. All rocks have a certain rupture strength, which means that they will continue to bend, rather then break, as long as the stress imposed on them does not exceed this rupture strength. When the stress finally becomes too great, the rocks fracture suddenly and move along a plane (the fault) that may or may not have existed before the deformation began. That sudden movement snaps the rocks on each side of the fault back into their original shape and produces an earthquake.
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