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This fault scarp was created by the 1959 Hebgen Lake, Montana, earthquake. Photo taken August 19, 1959.

A fault scarp is the topographic expression of faulting due to the displacement of the land surface by movement along the fault. It can be caused by differential erosion along an old inactive fault (a sort of old rupture) with hard & weak rock, or by an active geologic fault. In many cases, bluffs form from the upthrown block and can be very steep. The height of the scarp formation is equal to the vertical displacement along the fault. Active scarps are usually formed by tectonics, e.g. when an earthquake changes the elevation of the ground, and can be caused by any type of fault, including strike-slip faults, whose motion is primarily horizontal. This movement is usually episodic, with the height of the bluffs being the result of multiple movements over time. Displacement of around 5 to 10 meters per tectonic event is common.

Due to the dramatic uplift along the fault, the fault scarp is very prone to erosion, especially if the material being uplifted consists of unconsolidated sediment. Weathering, mass wasting and water runoff can soon wear down these bluffs.Fault scarps may be only a few centimeters or many meters high. Fault-line scarps are coincident with faults, but are most typically formed by the erosion of weaker rocks that have been brought alongside more resistant ones by the fault's movements. In the case of old eroded fault scarps, active erosion may have moved the physical cliff back away from the actual fault location which may be buried beneath a talus (fan) or the valley fill.

The rapid erosion of these bluffs can create defined V-shaped valleys along runoff channels. Adjacent V-shaped valley formations give the remaining fault spurs a very triangular shape. This formation is known as a triangular facet; however, this landform is not limited to fault scarps.

The Teton Range in Wyoming is an example of an inactive fault scarp. The Hurricane Cliffs, west of Zion National Park in Utah is a prominent example of a fault scarp along an old essentially inactive fault. Other examples include the scarps bounding the East African Rift Valley and the Rio Grande Rift in New Mexico.

In other parts of the world, many fault scarps in the Eastern and Western Alps should be mentioned, or a famous one in New Zealand. It can be seen at Maruia Falls on the Shenandoah Highway (State Hwy 65), South Island. The 1929 Murchison Earthquake raised the upstream side by about four metres thereby creating a fault scarp and as a result also, a waterfall.

Easterbrook, D. J. (1999) Surface processes and landforms. (Second Ed). Prentice Hall, Upper Saddle River, New Jersey.

See also: embankment, steepening, valley shoulder.

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