Abstract

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 to 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.

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