Daniel M. Horns’s research while affiliated with Utah Valley University and other places

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Publications (1)

(A) The Fort Canyon segment boundary (FCSB) is the fault linking the Salt Lake City and Provo segments of the Wasatch fault zone (WFZ). Within the segment boundary the fault trace (yellow and black lines) is more complex than the adjacent fault segments (Toké et al., 2017). The Traverse Ridge site (TR site: this paleoseismic study) is located at the crest of Traverse Ridge, midway along the FCSB. Adjacent paleoseismic sites include the South Fork Dry Creek site (SFDC site: Schwartz and Lund, 1988; Black et al., 1996), the Corner Canyon site (CC site: DuRoss et al., 2018), the Three Falls Ranch site (3FR site: Western GeoLogic, 2004), the Alpine site (Alp site: Bennett et al., 2018), and the American Fork site (AF site: Forman et al., 1989). (B) The WFZ extends for more than 300 km along the urban areas of the Wasatch Front (black regions). This study focuses on the Salt Lake City and Provo fault segments (yellow lines) which cut along the eastern edge of the urbanized area, within 10 km of more than 50% of Utah’s residents. Other segments (red lines) of the central WFZ include the Brigham City segment (BCS), the Weber segment (WS), and the Nephi segment (NS). The FCSB study area (A) is shown with a white box. Waterbodies (blue) and other Quaternary active faults are shown as faint gray lines over a shaded relief base map.
(A) The Traverse Ridge site (TR site) consists of seven ∼500-m-long paleoseismic trenches (T1-T7) that were originally investigated as part of a geotechnical investigation for a now abandoned housing development. In this study, we reoccupied the westernmost trench (T1). We re-excavated two portions of T1, which crossed two prominent fault traces. Trench 1 north (T1N: small blue rectangle) was cut across the northern fault trace and reoriented, extending fault-perpendicular for about 14 m along a 170° trend from the existing trench at approximately 40.49254°, -111.80467°. Trench 1 south (T1S: small green rectangle) was exposed along the southern fault trace by widening the existing trench, which was already well oriented, perpendicular to the fault. Base map is a lidar-derived shaded relief map with a 315° illumination angle. Fault traces (yellow lines) and queried slope discontinuities (dashed black lines) are from Toké et al. (2017). (B) Topographic profile and cross-sectional interpretation from X to X′. The northern and southern fault scarps cut through Tertiary volcanic (Tv) and alluvial fan (Taf) units (Biek, 2005). Quaternary colluvium (Qc) is observed on the hanging wall of the fault traces. The approximate locations and trench lengths are shown for T1N and T1S. (C) Three-meter contours overlain on a shaded relief map just to the west of the trench site. Here, it appears that the southern fault trace intersects and cuts the northern fault trace (within black box). This observation corresponds to trenching results that demonstrate a younger rupture in the T1S trench (Figures 3–7).
The east wall of Trench One North (T1N) presents evidence for three earthquake-produced colluvial wedges (C0, C2, and C3) along three fault zones. Age ranges are constrained for the C2 and C3 events. Sample TR-7 (0.3 – 0.5 ka) on this wall is helpful for constraining the age of the event associated with C3 (Figures 7, 8 and Table 1). Other samples constraining these events are found on the west wall (Figure 4 and Table 1). Undated samples and samples that were not included in the event age modeling are shown in italics and smaller font.
Trench One North (T1N) west wall presents evidence for three earthquake-produced colluvial wedges (C0, C2, and C3) along three fault zones. Ages are constrained for the C2 and C3 events. Samples TR16 (0.3 – 0.4 ka), TR17 (0.5–0.6 ka), and TR13a/b (3.4 – 3.5 ka and 3.6 – 3.8 ka) help constrain the age of the event that produced C3. Samples TR10a (7.0 – 7.3 ka), TR6 (8.8 – 9.3 ka), and TR-A (8.0 – 8.2 ka) help constrain the age of the event associated with C2 (Figures 7, 8 and Table 1). Stratigraphic relations of supporting samples are observed on the T1N east wall (Figure 3). Undated samples are shown in italics and smaller font.
Trench One South (T1S), east wall. Paleoseismic logging interpretation and photomosaic. The most recent event at TR site occurred along fault zone B, forming the CB colluvial wedge. This event is constrained to between 0.2 and 0.4 ka by samples TR25a – d and TR28a – b (Figures 7, 8 and Table 2). The CB colluvial wedge has been significantly modified by erosion on the west wall (Figure 6). Based upon the presence of older soil A-horizon material within the fault zone B (FZB) fissure (TR29), we infer that an older Holocene event occurred along this fault between 1.3 and 6.2 ka. However, the primary evidence for this event has been removed due to erosion. The older CA colluvium is massive and was undifferentiable. We expect it is colluvium derived from recurrent motion along FZA, but we did not document any evidence to constrain events along this fault zone. Undated samples are shown in italics and smaller font.

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The Traverse Ridge Paleoseismic Site and Ruptures Crossing the Boundary Between the Provo and Salt Lake City Segments of the Wasatch Fault Zone, Utah, United States
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March 2021

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202 Reads

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3 Citations

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Christopher Langevin

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Daniel M. Horns

How structural segment boundaries modulate earthquake behavior is an important scientific and societal question, especially for the Wasatch fault zone (WFZ) where urban areas lie along multiple fault segments. The extent to which segment boundaries arrest ruptures, host moderate magnitude earthquakes, or transmit ruptures to adjacent fault segments is critical for understanding seismic hazard. To help address this outstanding issue, we conducted a paleoseismic investigation at the Traverse Ridge paleoseismic site (TR site) along the ∼7-km-long Fort Canyon segment boundary, which links the Provo (59 km) and Salt Lake City (40 km) segments of the WFZ. At the TR site, we logged two trenches which were cut across sub-parallel traces of the fault, separated by ∼175 m. Evidence from these exposures leads us to infer that at least 3 to 4 earthquakes have ruptured across the segment boundary in the Holocene. Radiocarbon dating of soil material developed below and above fault scarp colluvial packages and within a filled fissure constrains the age of the events. The most recent event ruptured the southern fault trace between 0.2 and 0.4 ka, the penultimate event ruptured the northern fault trace between 0.6 and 3.4 ka, and two prior events occurred between 1.4 and 6.2 ka (on the southern fault trace) and 7.2 and 8.1 ka (northern fault trace). Colluvial wedge heights of these events ranged from 0.7 to 1.2 m, indicating the segment boundary experiences surface ruptures with more than 1 m of vertical displacement. Given these estimates, we infer that these events were greater than Mw 6.7, with rupture extending across the entire segment boundary and portions of one or both adjacent fault segments. The Holocene recurrence of events at the TR site is lower than the closest paleoseismic sites at the adjacent fault segment endpoints. The contrasts in recurrence rates observed within 15 km of the Fort Canyon fault segment boundary may be explained conceptually by a leaky segment boundary model which permits spillover events, ruptures centered on the segment boundary, and segmented ruptures. The TR site demonstrates the utility of paleoseismology within segment boundaries which, through corroboration of displacement data, can demonstrate rupture connectivity between fault segments and test the validity of rupture models.

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Citations (1)

... California, which lies on a strike-slip transition zone between the Pacific plate and the North American plate, is characterized by the presence of the NW-trending San Andreas dextral strike-slip fault system, with the strike-slip faults commonly showing strong Quaternary activity [67,68]. The Basin and Range Province, which is a dispersion deformation zone subjected to a nearly NW intraplate extension, is characterized by the presence of a few hundred to a thousand smallsized but generally potentially active normal faults with earthquake recurrence intervals spanning from thousands to tens of thousands of years [69][70][71]. The central-eastern part of the North American continent, most parts of which are relatively stable regions, is prevalently characterized by the reactivation of Paleozoic to Mesozoic old structures under a nearly E-W to NE horizontal compressional tectonic stress field [72]. ...

Reference:

Definitions, Classification Schemes for Active Faults, and Their Application
The Traverse Ridge Paleoseismic Site and Ruptures Crossing the Boundary Between the Provo and Salt Lake City Segments of the Wasatch Fault Zone, Utah, United States

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Christopher Langevin

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Daniel M. Horns