Abstract

Fault scarps represent the most obvious expression of tectonic activity at the Earth's surface. Studies on scarp morphology place constraints on fault kinematics and scarp-degradation processes, and were often based on geomorphic dating techniques. Fault scarps exposed in areas of simple topography facilitate data acquisition and interpretation, whereas little work had been done where fault scarps are superimposed on complex, dissected topography. Fault scarps developed in complex topography are commonly observed along flower structures and at tips of strike-slip faults. Such structures are important elements for evaluating the evolution and linking of strike-slip fault systems, and appear to be scale-independent from several meters to hundreds of kilometers. We examined the detailed meter- to hundred meter–scale structure and surface expression of a flank of one fault scarp–bounded pressure ridge (Rex Hills flower structure) by combining field mapping with high-resolution digital elevation model (DEM) analysis. Based on terrestrial laser scanning we generated a detailed DEM and extracted high-resolution topographic cross sections, which enabled us to identify fault scarps and to determine their relative ages and geometry. Our study site is located on the transpressional left-bend between the Pahrump and Amargosa segments of the dextral Stateline fault system. The topography is characterized by alternating valleys and ridges (each ∼100 m long, relief of ∼4 m). We observed the following: the southern Rex Hills slope exhibits three fault scarps related to three reverse fault branches; the basal scarp (scarp 1) is most continuous, and exhibits five segments, the upper two scarps (scarps 2 and 3) are less continuous. Furthermore, fault scarps exposed on ridge crests are more numerous (up to four to five scarps), and smaller (∼5 m high); valleys often exhibit single large (>10 m high), smoothed scarps. To easily detect differences between the scarps, we evaluated the height and slope angle of the scarps using topographic cross sections. Our analysis indicates that scarp shape is influenced by fault dip, lithology, and degradation processes resulting in large scatter and broad overlap in scarp-height–slope-angle space. The analysis further indicates that scarp degradation is stronger in the valleys, and that the preservation potential of small, individual fault scarps is therefore greater on the ridge crests. We compared our fault-scarp data with published, calibrated data yielding an age of ∼2 ka for the Rex Hills scarps consistent with an earlier finding. This suggests that the scarp shape mainly reflects progressive degradation since the most recent surface rupture. Our approach of analyzing high-resolution topographic data of closely spaced fault scarps is promising especially when combined with subsurface data as well as geochronological and paleoseismic data, and it provides a basic scheme for analyzing scarp populations in a complex topographic region. Despite the absence of subsurface data, our approach allowed the study of complex high-resolution fault-scarp morphologies across a flower structure for the first time.

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