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 the
United States Geological Survey points out that an event may be of the order of days, weeks, or months. 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. Earthquake swarms are one of the events that typically precede eruptions of
volcanoes.