Geomorphic evidence for Holocene earthquakes in the Olinghouse fault zone, Western Nevada

Mapping and morphologic analysis of young fault scarps in the Olinghouse fault zone of western Nevada yields information about the ages and magnitudes of Holocene-late Pleistocene surface-rupturing earthquakes. Twenty profiles of single-event scarps in the eastern third of the fault zone yield ages that average 4.5 +/- 2.0 ka. Ages were determined assuming linear diffusion of scarp material, with the diffusion coefficient as a function of scarp offset determined from profiles of Lake Lahontan high-stand shorelines located nearby. The mid-Holocene age is consistent with the observation that the scarps are cutting alluvial material that buries the 15.4-ka shorelines. The minimum length of faulting during this earthquake was 8 km, and the maximum normal fault offset was about 1 m, suggesting an earthquake of about M 6.7. Several older scarp segments have cumulative normal offsets of 2.5 to 4.8 m and one or two crest bevels above the most recent scarp slope, suggesting that two to three earthquakes have formed these scarps. The average diffusion age of five multiple-event scarp profiles is about 13 ka. If this represents a weighted average of the ages of the earthquakes that formed the scarps, then two or three large earthquakes have occurred since about 21 ka, which gives a speculative average recurrence period of 8 of 16 kyr. Historical accounts and geomorphic evidence of young left-slip offsets of up to 3.6 m (M 7.1) at the western end of the Olinghouse fault zone suggest that it may have ruptured historically. Thus, the potential exists for large earthquake generation all along the 20+ km length of the fault zone.