a zone along a tectonically active area where no earthquakes have occurred recently, but it is known that elastic strain is building in the rocks

An area in an earthquake-prone region where there is a below-average release of seismic energy.

a locked fault segment that has not experienced seismic activity for a long time. Because stress tends to accumulate in seismic gaps, they often become the sites of major earthquakes.

A section of a fault that has produced earthquakes in the past but is now quiet. For some seismic gaps, no earthquakes have been observed historically, but it is believed that the fault segment is capable of producing earthquakes on some other basis, such as plate-motion information or strain measurements.

A segment of an active fault zone that has not experienced a major earthquake during a time interval when most other segments of the zone have. Seismologists commonly consider seismic gaps to have a high future-earthquake potential.