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SECTI®IIFOUR SCIsmIC NEW Inputs The Williams Fork Valley is a northwest-trending structural graben, bounded by the main WFMF to the southwest and a couple of apparently less-active unnamed antithetic normal faults to the northeast (Figure 4; Kirkham, 2004). The Tertiary and Quaternary sediments filling the graben are also crosscut by several northeast-striking normal faults (Olig et al., 2013). All of these faults are collectively referred to in the USGS database as the unnamed faults of Williams Fork Valley(#2300),and are discussed further in the following section. As a result of recent mapping and paleoseismic trench investigations, Olig et al. (2013) shortened the maximum extent of the WFMF to 37 km, with the Quaternary portion interpreted to be 32 km long. On the basis of geomorphic and geologic characteristics,they also identified three sections of the fault: northern, central and southern (Figure 4 and Table 3). The northern section is the youngest, most-active, and longest section, whereas the southern section is the oldest, least-active,and shortest section, and the central section is intermediate in age, length and activity (Table 3; Olig et al., 2013). Of particular note, scarps on latest Quaternary deposits are prominent along the northern section (Kirkham, 2004), Quaternary scarps are scarce along the middle section, and apparently absent along the southern section (Olig and Kirkham, 2012). Olig and Kirkham (2012) refer to these portions of the WFMF as "sections" rather than "segments" because they do not think that it is likely that the middle and southern sections will rupture independently in large surface-faulting earthquakes given their short lengths, and the apparent pattern of decreasing rates and increasing age of most recent rupture to the southeast, which suggests that activity may be dying off to the southeast. Results from paleoseismic trenching on both the northern and central sections also indicate a younger, more active northern section. A trench across a fault scarp on a Pinedale-age alluvial fan at Johnson Gulch near the northern end of the fault (Figure 4) revealed evidence for the remnants of a colluvial wedge associated with a surface-faulting earthquake that occurred about 7.0 f 0.8 ka based on analysis of 5 radiocarbon ages (Olig et al., 2013). Direct stratigraphic evidence for older events was eroded away, but the exposure did reveal that much of the 5-m- high scarp was actually held up by Tertiary Troublesome Formation overlain by older alluvial fan deposits that were then draped by younger Pinedale-age fan deposits, suggesting that not all of the slip that formed the scarp actually occurred post-Pinedale, as was assumed by previous scarp profile studies of the site(Unruh et al., 1993;Kirkham,2004). In particular,the maximum slip rate estimate of 1.3 mm/yr made by Unruh et al. (1993), which was based on 13 m of vertical slip occurring since 10 ka, seems highly unlikely given the evidence of one early Holocene event and the overall stratigraphic and structural relations exposed in the trench (Olig et al.,2013). In comparison, a trench across a short scarp on alluvial fan deposits along the middle section north of Ute Creek revealed that the scarp was actually not fault-related but was depositional. No faults or other evidence of faulting was exposed,but older alluvium(>>8 ka)appeared back- tilted toward the range front,providing suggestive evidence of older(pre-Holocene)deformation along the main range-front fault to the southwest, which now appears buried along much of the middle section(Olig et al.,2013). Based on the paleoseismic results, Olig et al. (2013) included three rupture scenarios for the WFMF and we retain those here: A) the northern section only; B) the northern and middle sections; and, C) the northern, middle and southern sections (Figure 3). Using the empirical UM127-MAR48N 13