Earthquake swarm

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February 2008 swarm near Mexicali.

Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to define the swarm itself varies, but may be of the order of days, weeks, or months.[1] They are differentiated from earthquakes succeeded by a series of aftershocks by the observation that no single earthquake in the sequence is obviously the main shock.


  • Between February and April of 2008 a swarm of 1,000 small magnitude quakes in the United States, referred to as the 2008 Reno earthquakes began in February and ended in November.[2]
  • During the 2011–12 El Hierro eruption. From July 2011 until October 2011, hundreds of small earthquakes were measured. The accumulated energy released by the swarm increased dramatically on 28 September.[3] The swarm was due to the movement of magma beneath the island, and on 9 October indications of a submarine volcanic eruption were detected.[4]
  • In 2014, an area near the California/Oregon/Nevada borders experienced more than 800 small earthquakes over a period of around three months.[6] More than 550 quakes were on magnitude 2.0 or larger.[7]

See also[edit]