FIGURE 8.9 Basic slope elements that may be present on a fault scarp. After Wallace (1977).

FIGURE 8.10 Change in slope elements (fault-scarp morphology) with time for fault-scarp degradation in the Great Basin area of Nevada. After Wallace (1977).

can be recognized by sharp breaks in slope on the scarp, benches or terraces associated with small channels that have eroded through the fault scarp, knickpoints (short vertical or steep sections) in channels that cross the scarp, scarp height that exceeds that likely produced by a single event, and progressive displacement (older material has been displaced more than younger material).

Change in fault-scarp morphology with time is being treated quantitatively. Bucknam and Anderson (1979) developed relations between scarp height and scarp-slope angle for fault scarps in Utah with estimated ages ranging from 1000 to 100,000 yr (Figure 8.11). Their studies verify Wallace’s (1977) conclusion that with

TABLE 8.1 Fault Scarp-Slope Morphologya

Slope Element

Morphology

Process (Formation and/or Modification

Comments and General Chronology

Crest

Top of fault scarp (break in slope); initially sharp, becomes rounded with time

Produced by faulting; modified by weathering, mass wasting

Becomes rounded after free face disappears; usually rounded after about 10,000 yr

Free Face

Straight segment; initially 45° to overhanging

Produced by faulting; modified by weathering, gullying, mass wasting; eventually buried from below by accumulation of debris

Dominant element for 100 year or so; disappears after about 1000–2000 yr

Debris Slope

Straight segment; at angle of repose of material usually 30° to 38°

Accumulation of material that has fallen down from the free face

Is dominant element after about 100 yr, remains dominant until about 100,000 yr, disappears at about 1,000,000 yr

Wash Slope

Straight to gently concave segment; overlaps the debris slope; slope angle generally 3° to 15°

Fluvial erosion and deposition; deposition of wedge or fan of alluvium near toe of the slope; some gullying

Is developed by 100 yr, significant by 1000 yr, and dominant by 100,000 yr

Toe

Base of fault scarp (break) in slope) slope; may be initially sharp, but with time may become indeterminate as grades into original slope

Fluvial erosion and deposition; owing to change in process/form from upslope element (free face, debris slope, or wash slope) to original surface below the fault-scarp slope

More prominent in young fault scarps or where wash slope is not present; on scarps older than about 12,000 yr. the basal slope break is sharper than the crestal slope break

aAfter Wallace (1977) for fault scarps in the Great Basin.



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