Seismic Swarm

A seismic swarm, also called an earthquake swarm, is a sequence of earthquakes striking a local area within a relatively short span of time, which may last days, months or even years. It differs fundamentally from an ordinary mainshock aftershock sequence, in which one major rupture is followed by progressively smaller tremors: in a swarm, no single earthquake stands out as the main shock, and the sequence instead consists of multiple events of broadly comparable size clustered in time and place. A cluster of aftershocks following a genuine mainshock is explicitly not considered a swarm.