Low‐angle normal faults in the basin‐and‐range province

Abstract

Published data imply that normal faults in general are steeply inclined, and it is commonly assumed that faults of this class have developed habitually with dips of 45° or more. The writer has not seen in the literature many descriptions of large normal faults that have conspicuously low dips. Those that dip 25° or less usually are assumed to have been rotated from initially steep inclinations. Moreover, few published descriptions of large normal faults known to the writer cite evidence of decreasing dip with increasing depth, to indicate concavity of fault‐surfaces toward the hanging wall. Indeed, some structural geologists have argued that evidence favors steepening of ordinary normal faults downward, with resulting concavity toward the footwall‐block [see 12 of “References” at end of paper]. Pronounced concavity of a fault‐surface toward the hanging wall has been interpreted as a characteristic of superficial “landslide‐faulting”