This article is about the geological event. For other uses of the term see Aftershock (disambiguation).

Aftershocks are earthquakes in the same region of the central shock (generally within a few rupture length) but of smaller magnitude and which occur with a pattern that follows Omori's law. Omori's law, or more correctly the modified Omori's law, is an empirical relation for the temporal decay of aftershock rates. Omori published his work on the aftershocks of earthquakes, in which he stated that aftershock frequency decreases by roughly the reciprocal of time after the main shock, in 1894.