Page "Earthquake" Paragraph 23
from
Wikipedia
Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time.
They are different from earthquakes followed by a series of aftershocks by the fact that no single earthquake in the sequence is obviously the main shock, therefore none have notable higher magnitudes than the other.
In August 2012, a swarm of earthquakes shook Southern California's Imperial Valley, showing the most recorded activity in the area since the 1970s.
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