Living Reference Work Entry

Encyclopedia of Earthquake Engineering

pp 1-16

Date: Latest Version

Earthquake Swarms

  • Josef HorálekAffiliated withInstitute of Geophysics, Academy of Sciences of the Czech Republic Email author 
  • , Tomáš FischerAffiliated withFaculty of Science, Charles University in Prague
  • , Páll EinarssonAffiliated withFaculty of Earth Science, University of Iceland
  • , Steinunn S. JakobsdótirAffiliated withFaculty of Earth Science, University of Iceland


b-value; Clustering of events; Driving forces; Earthquake location; Earthquake swarms; Focal migration; Mainshock-aftershock sequence; Source mechanism, Fluids; Triggering mechanisms; Volcanic activity.


Earthquake swarms are a specific type of seismicity. They are generally defined as sequences of seismic events closely clustered in space and time, without a single outstanding earthquake (Mogi 1963). Globally, most seismic energy is released in ordinary earthquakes, represented by a single strong event succeeded by a series of smaller aftershocks (in some cases also preceded by foreshocks) with magnitudes of one or more magnitude units lower than that of the main event. These are so-called mainshock-aftershock sequences. In contrast, an earthquake swarm consists of numerous, mostly shallow, earthquakes, which are missing a single large event. They produce few dominant earthquakes of similar magnitudes so that smaller events are not associated with any identifiable ma ...

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