aftershock A small seismic event that follows a prior larger earthquake. When the aftershock proves to be bigger than the preceding event, then the former is re-labelled foreshock and the latter an earthquake.
Aftershock Geomedicine A mini-earthquake that follows the largest shock of an earthquake sequence, which falls within 1–2 fault-lengths distance from the main shock; aftershocks and can continue for weeks, months, or years. See Earthquake. Cf Foreshocks.