1. n. [Geology]

A relatively low-standing fault block bounded by opposing normal faults. Graben (used as both singular and plural) can form in areas of rifting or extension, where normal faults are the most common type of fault. Between graben are relatively high-standing blocks called horsts. A half-graben is a downdropped block bounded by a normal fault on only one side.

See: aulacogen,  horst,  normal fault,  rift,  strike-slip fault