Geology glossary

Aftershocks are smaller quakes that follow a usually larger earthquake in the same rupture zone. The can occur up to weeks, months or even years after, depending on the size of the main shock.

Aftershocks are smaller than the mainshock and occur within 1-2 rupture lengths distance from the mainshock.
In general, the larger the mainshock, the larger and more numerous the aftershocks, and the longer they will continue. Large earthquakes can be followed by thousands of aftershocks.
The larger aftershocks following an earthquake can be particularly dangerous if many structures have been weakened or damaged already by the mainshock.