Holocene Earthquakes and Late Pleistocene Slip-Rate Estimates on the Wassuk Range Fault Zone, Nevada

Abstract

The Wassuk Range fault zone is an 80-km-long, east-dipping, high-angle normal fault that flanks the eastern margin of the Wassuk Range in central Nevada. Observations from two alluvial fan systems truncated by the fault yield information on the vertical slip rate and Holocene earthquake history along the range front. At the apex of the Rose Creek alluvial fan, radiocarbon dating of offset stratigraphy exposed in two fault trenches shows that multiple earthquakes resulted in 7.0 m of vertical offset along the fault since ∼9400 cal B.P. These data yield a Holocene vertical slip rate of 0:7 0:1 mm=yr. The south trench exposure records at least two faulting events since ∼9400 cal B.P., with the most recent displacement postdating ∼2810 cal B.P. The north trench exposure records an ∼1 m offset between ∼610 cal B.P. and A.D. ∼1850, a 1.3-m minimum offset prior to ∼1460 cal B.P., and one earlier undated earthquake of a similar size. Variations in stratigraphy and limited datable material preclude a unique correlation of paleoevents between the two trenches. Approximately 25 km north, the range-front fault has truncated and uplifted a remnant of the Penrod Canyon fan by > 40 m since the surface was deposited ∼113 ka, based on cosmogenic dating of two large boulders. These data allow an estimate of the minimum late Pleistocene vertical slip rate at > 0:3-0:4 mm=yr for the Wassuk Range fault zone. Online Material: Tables summarizing radiocarbon and cosmogenic analyses, photos of rocks sampled for cosmogenic analyses, and figures summarizing cosmogenic exposure age estimates.

The unusual temporal and spatial slip history of the Wassuk Range normal fault, western Nevada (USA): Implications for seismic hazard and Walker Lane deformation

“…This work also suggests that many of the apparent single-event Holocene scarps mapped along the range front (e.g., Demsey, 1987) may in fact be unrecognized multiple event scarps . Significantly, both of the Rose Creek study locations displayed apparent single -event scarp morphologies ; thus, we place higher confidence in the vertical displacement rate estimated by Bormann et al (2012).…”

“…The impressive topographic relief along the fault zone and previous geologic studies have established that displacement along the fault zone has been characterized by significant normal displacement across all time scales during Tertiary and Quaternary time (e.g., Dilles, 1993;Stockli et al, 2002;Surpless et al, 2002;Wesnousky, 2005;Surpless, 2011;Bormann et al, 2012;Wesnousky et al, 2012;Dong et al, 2014).…”

“…However, Bormann et al (2012) used observations and age data from two trenches at the apex of the Rose Creek alluvial fan (Fig. 1) to establish that at least three significant seismic events have occurred since ∼9400 cal B.P., with the most recent displacement postdating ∼2810 cal B.P., perhaps as young as ∼1850 A.D.…”

“…2) were 0.4 -0.7 mm/yr and 0.9 -1.0 mm/yr, respectively . To convert these values from horizontal extension rate to vertical displacement rate, we assumed a range in fault dips between 45° and 60°, consistent with previous studies of the range-bounding fault (e.g., Dilles, 1993;Stockli et al, 2002;Surpless, 2010;Bormann et al, 2012), and we calculated vertical displacement rate using the equation:…”

“…Vertical displacement rates have been constrained for the Wassuk Range normal fault system since post-Pliocene time (10 6 -yr timescale; Stockli et al, 2002;Surpless, 2011), Late Pleistocene time (10 4 -yr timescale; Dong et al, 2014), and Holocene time (10 3 -10 4 -yr timescale; Bormann et al, 2012).…”