Earthquake Groups

Earthquakes are often followed by aftershocks. Sometimes, an earthquake turns out to have been a foreshock for a larger event. Or there is no clear mainshock, instead several earthquakes of a similar size occur in a relatively small area in a relatively short amount of time, i.e., a "swarm" of earthquakes. The event groups on this page are examples of interesting mainshock-aftershock sequences or swarms.