Profiles and ages of young fault scarps, north-central Nevada

Abstract

The geomorphic characteristics of young fault scarps can be used as a key to the ages of fault displacements. The principal features of scarps younger than a few thousand years are a steep free face, a debris slope standing at about 35°, and a sharp break in slope at the crest of the scarp. The principal slope of older scarps declines with age, so that scarps of about 12,000 yr of age have maximum slope angles of 20° to 25°, and slopes as low as 8° to 9° represent ages much older than about 12,000 yr. The crestal break in slope broadens with age. The material in the scarp face, whether loose fanglomerate or indurated bedrock, controls to a large extent the rate of scarp degradation. Where more than one displacement has occurred along a fault, a composite or multiple scarp develops. Composite or multiple scarps suggest mean recurrence intervals on individual faults measured in thousands of years.