Tectonics and Landforms

Types of Faults

Faults are distinguished on the basis of the movement of the footwall relative to the hanging wall (Figures TL.23a-d).  Dip slip faults are those in which vertical displacement primarily occurs.  A normal fault is one in which the hanging wall falls down relative to the foot wall due to tensional stress . The Teton Mountains in North America are a result of normal faulting. A graben forms when a block of rock falls between two faults. Huge, relatively flat bottomed valleys, like Death Valley in California , are created in this way. A reverse fault  is one in which the hanging wall moves up relative to the foot wall due to compression . If the hanging wall is pushed up and then over the foot wall at a low angle it is called a thrust fault. A horst is formed when a block of rock is pushed up between two faults. Large plateau surfaces form in this fashion. The Basin and Range Province of North America is noted for its faulted mountains and flat-bottomed valleys.

Figure TL.29 The Great Basin located in the upper center of this shaded relief map is composed of parallel mountain ranges with intervening basins caused by faulting (Courtesy USGS)

Strike slip or transform  faults are those that primarily exhibit horizontal movement . Such activity can be discerned from surface features like offset streams. The San Andreas fault is a well-known strike slip fault caused by the Pacific Plate sliding past the North American Plate. (View a segment of the San Andreas fault in Google Earth) Oblique faults exhibit both horizontal and vertical movement.  

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