Graben

Graben
In geology, a graben is a depressed block of the crust of a planet or moon, bordered by parallel normal faults.
Etymology
Graben is a loan word from German, meaning 'ditch' or 'trench'. The first known usage of the word in the geologic context was by Eduard Suess in 1883. The plural form is either graben or grabens.
Formation
A graben is a valley with a distinct escarpment on each side caused by the displacement of a block of land downward. Graben often occur side by side with horsts. Horst and graben structures indicate tensional forces and crustal stretching.
Graben are produced from parallel normal faults, where the displacement of the hanging wall is downward, while that of the footwall is upward. The faults typically dip toward the center of the graben from both sides. Horsts are parallel blocks that remain between graben; the bounding faults of a horst typically dip away from the center line of the horst. Single or multiple graben can produce a rift valley.
Half-graben
In many rifts, the graben are asymmetric, with a major fault along only one of the boundaries, and these are known as half-graben. The polarity (throw direction) of the main bounding faults typically alternates along the length of the rift. The asymmetry of a half-graben strongly affects syntectonic deposition. Comparatively little sediment enters the half-graben across the main bounding fault because of footwall uplift on the drainage systems. The exception is at any major offset in the bounding fault, where a relay ramp may provide an important sediment input point. Most of the sediment will enter the half-graben down the unfaulted hanging wall side (e.g., Lake Baikal).
Examples
Africa
East African Rift Valley
Lucapa Graben, Lunda Norte Province, Angola
Antarctica
Lambert Graben, Antarctica
Asia
Narmada River Valley, central India
lower Godavari River Valley, southern India
Baikal Rift Zone, Siberia, Russia
Moma Graben, Sakha Republic, Russia
Büyük Menderes Graben, Turkey
Fossa Magna, Honshu, Japan
Ariake Sea as part of the Unzen graben, Kyushu, Japan
Beppu–Shimabara graben, Kyushu, Japan
Europe
Rhine valley, border area of west Germany and northeast France
Oslo graben around Oslo, Norway
Central Lowlands, Scotland
Worcester Basin, England
Central Graben, North Sea
Viking Graben, North Sea
Vättern, Sweden
Lowtherville Graben, Ventnor, Isle of Wight, England
North America
Canada
Ottawa-Bonnechere Graben, Ontario and Quebec, Canada
Saguenay Graben, Quebec, Canada
Guatemala
Guatemala City valley, Guatemala
United States
Basin and Range Province of southwestern North America is an example of multiple horst/graben structures, including Death Valley, with Salt Lake Valley being the easternmost and Owens Valley being the westernmost.
Lake George Basin, New York, U.S.
Lake Tahoe Basin, California and Nevada, U.S.
Republic Graben, Republic, Washington, U.S.
Rio Grande Rift Valley in Colorado/New Mexico/Texas of the United States
Rough Creek Graben, Kentucky, U.S.
Santa Clara Valley, California, U.S.
Western Snake River Plain, Idaho, U.S.
Southwest San Bernardino Valley (Arizona), U.S.
Multi-national
Eastern North America Rift Basins, Canada and the U.S.
Midcontinent Rift System, Canada and the U.S.
Salton Trough, Mexico and the U.S.
Oceania
Firth of Thames of Hauraki Gulf and Hauraki Plains of Hauraki Rift (Hauraki half grabens), North Island, New Zealand
Tikitere Graben within the Taupō Rift, North Island, New Zealand.
Gulf St Vincent, South Australia, Australia
Tamar Valley, Tasmania, Australia
South America
Guanabara Graben, Rio de Janeiro, Brazil
See also
European Cenozoic Rift System
Notes
References
Structural geology
Tectonic landforms