Earthquake Glossary - rupture front
The rupture front is the instantaneous boundary between the slipping and locked parts of a fault during an earthquake. Rupture in one direction on the fault is referred to as unilateral. Rupture may radiate outward in a circular manner or it may radiate toward the two ends of the fault from an interior point, behavior referred to as bilateral.
Snapshots of a rupture front moving across a fault surface.