What term describes the smaller earthquakes that follow a main earthquake?

Aftershocks are smaller earthquakes that follow a larger main earthquake in the same general region.

They occur as the crust adjusts to changes in stress caused by the mainshock. The number of aftershocks usually decreases over time, a pattern described by the modified Omori law. Some aftershocks can still be damaging, especially when buildings have already been weakened.

An aftershock is defined relative to a mainshock, not by a fixed magnitude. A large earthquake can therefore be followed by aftershocks that would themselves be significant earthquakes elsewhere. The sequence may continue for days, months or, after very large earthquakes, years.

The term is commonly confused with foreshock. An earthquake can be called a foreshock only if a larger event later occurs in the same sequence; before that larger event, it may simply appear to be an ordinary earthquake.