Graben

A graben is a depressed block of the Earth's crust that is bounded by two roughly parallel normal faults, forming an elongated downward-right-lowing block. The term is borrowed from the German graben, meaning ditch or trench. Graben structures are characteristic of extensional tectonic regimes and are common in continental rift zones as well as in regions undergoing crustal thinning.

Graben formation occurs when the crust is extended and blocks slide downward along dip-slip faults relative to adjacent blocks. If subsidence occurs on both sides of a central block, the central block becomes a graben. If subsidence is more pronounced on one side, a half-graben results, with the opposing boundary forming a faulted margin; uplifted blocks between faults are called horsts.

Graben systems typically host elongated basins that fill with sediments, volcanic rocks, and lacustrine deposits. Their topography often features linear valleys bordered by fault scarps. Graben zones are important in geology and hydrology because thick sediment sequences can host groundwater resources and, in many cases, hydrocarbon reservoirs. They also provide insight into the history of crustal extension and continental breakup.

Prominent examples include the Rhine Graben in central Europe, the East African Rift system, the Rio Grande Rift in North America, and the Basin and Range Province in the western United States. These regions illustrate how graben formation contributes to regional tectonics, Basin development, and landscape evolution.