Schmidt hammer and terrestrial laser scanning (TLS) used to detect single‐event displacements on the Pleasant Valley fault (Nevada, USA)

Abstract

ABSTRACTChanges in surface roughness on carbonate fault scarps often reflect varying durations of subaerial weathering. On the Pleasant Valley fault in central Nevada, the documentation of a surface rupture in 1915, a long recurrence interval of faulting, slow weathering rate, and a relatively high (2–3 m) single‐event displacement make the discrimination of the historical and penultimate slip patches unambiguous. Following from a 2018 study, we used a Schmidt hammer and terrestrial laser scanning (TLS) to further test whether these weathering patterns delineate exposed slip patches on a fault scarp. Results show that Schmidt hammer rebound value ranges (termed ΔR – the difference between minimum and maximum R‐values in repeat impacts at a point), increase by ~8–10 points across the historical–penultimate event transition zone in two separate scarp transects. TLS‐derived surface roughness also indicates a clear difference between the most recent and penultimate events. The average single‐event displacement (SED) estimated using the Schmidt hammer and TLS is 2.85 m at two transect sites and is roughly equivalent to the visually estimated 3 m. While this fault is an ideal case where we know some of the slip history, the results demonstrate that these techniques show promise for discriminating slip patches on larger carbonate fault scarps with longer paleoearthquake histories, and could be used alongside 36Cl cosmogenic exposure‐age dating to improve paleoseismic records on normal faults. © 2019 John Wiley & Sons, Ltd.