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Influences of Tectonic and Geomorphic Processes on Fault Scarp Height

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Influences of Tectonic and Geomorphic Processes on Fault Scarp Height Influences of tectonic and geomorphic processes on fault scarp height variability in an extensional tectonic terrane, Teton fault, Wyoming Kyla Grasso1, Glenn Thackray Idaho State University Graduate Research Symposium April 6 2020 [email protected] Abstract Methods Discussion & Interpretation Landscape disturbance events (e.g., earthquakes, landslides, floods) play key roles in landscape Mapping Mapping evolution. Similarly, glacial and erosion processes alter landscapes along mountain range fronts, • A 1-m resolution LiDAR-derived digital elevation model (DEM) was used to generate hillshade and • Digital and field mapping led to new interpretations of lineaments previously mapped as fault introducing landscape complexity. Along the 70-km Teton fault, fault scarps vary in height by up slope models of the study area. Fault scarps, slope failure deposits, and landforms were mapped at scarps9 (Figure 3). to tens of meters over short (<1 km) distances. Variable scarp height may be due to 1) variable a scape of 1:6,000 using ArcGIS 10.7. offset rates of the Teton fault; 2) variable erosion of fault scarps by glacial processes; 3) variable • The relationships between fault scarps and landforms in the areas northeast of Jackson Lake, ages of landforms; 4) erosion and deposition by landslide and alluvial processes that have • Field mapping was used to confirm and refine digital mapping of scarps, landslide deposits, and south of Leigh Lake, and south of Phelps Lake have been clarified and mapped at a finer scale occurred since deglaciation; or 5) some combination of these factors, and possibly others. other geomorphic features. than in previous studies. Light detection and ranging (LiDAR)-based mapping of the fault zone indicates that scarp height Scarp profiling Scarp profiling Table 1. Summary of four proposed fault sections. is affected by glacial geomorphology, landslide, and alluvial processes. At a broad scale, scarp • Fault scarp topographic profiles were created • Normal faults are expected to Proposed Length Fault No. of Avg. Max. Min. height (vertical separation across scarps, VS) increases in the central portion of the fault. At a at ~1 km intervals along the fault. undergo the greatest slip rate, and section (km) strike profiles VS (m) VS (m) VS (m) Eagle Rest finer scale, scarps are lower in the floors of deglaciated valleys than on neighboring glacial thus have the greatest VS, toward Peak 27 NNE 19 11.9 21.3 1.0 moraines, reflecting both valley floor processes and younger landform ages. • Vertical separation was calculated by projecting the central portion of the fault10,11,12. Mount Moran 12 NNE 7 15.0 32.0 1.6 surface slopes across the scarp and finding the Middle The VS of normal fault scarps is expected to systematically increase toward the central portion distance between them, following the methods • This study identified four areas of Teton 16 NNE 11 12.1 14.8 6.6 of the fault. However, overall VS of Teton fault scarps is highest toward the south. Typical VS is of previous authors6,7,8 (Fig. 2). the where VS follows this pattern Rendezvous Figure 2. Schematic diagram of VS calculation Modified from Amos et al. Peak 17 NE 9 27.9 54.4 13.6 ~12 m from the north end of the fault to the south end of Jackson Lake, ~16 m from Jackson (2010). (Table 1). Lake to the south end of Jenny Lake, and ~11 m from the south end of Jenny Lake to Granite Results Canyon. South of Granite Canyon, the typical VS is ~28 m. The transition zones between these Mapping Conclusions areas may represent boundaries between fault sections or segments. • Digital and field mapping refined the most recently published map of the Teton fault and new • LiDAR-based mapping coupled with field interpretations of lineaments previously mapped as fault scarps9 (Fig. 3). mapping of select areas is effective for rapid reconnaissance of densely vegetated areas Study area Scarp profiling limited field accessibility. • Fault scarp profiles were used to measure VS along • The Teton fault forms a series of NNE-trending the fault (Fig. 4). • The anomalously high scarps along the scarps along the eastern range front (Fig. 1). The southern range front may be the result of study area extends ~1-km across the fault. Models • The highest scarps are found along the southern landform age, inherited scarp height, or suggest a recurrence interval of 700-2,000 yrs for range front (Fig. 4). other factors. large (M>7.0) earthquakes on the Teton fault1. • We propose a four-section model of the • Uplift of the range began with Laramide thrust Teton fault based on vertical separation faulting in Late Cretaceous and early Paleogene analysis (Table 1, Figure 5). time. The core of the range is composed of metamorphosed intrusive and metasedimentary • A four section (or possibly, segment) model rocks, and blanketed by Quaternary deposits2,3. of the Teton fault should be considered in natural hazards assessments. • The region underwent repeated glaciations during Pleistocene time. The most recent of these, the Pinedale glaciation, retreated from the study area Figure 5. Map view of the four-section model of the Teton fault. REFERENCES: 1) O’Connell, D.R.H., Wood, C.K., Ostenaa, D.A., Block, L.V., and LaForge, R.C., 2003, Ground Motion Evaluation for Jackson Lake Dam, Min-min.pdf: Seismotectonics and Geophysics Group, Technical Service Center, Bureau of Reclamation Final Report 2003–2, 493 p. 2. 2) Love, J.D., Reed, J.C., and Christiansen, A.C., 1992, Geologic Map of Grand Teton National Park, Teton County, Wyoming: United States Geological Survey, 1 p. 2. 3) Love, D.J., Reed, J.C., Jr., and ~15 ka, leaving behind a sequence of deglacial Pierce, K.L., 2003, Creation of the Teton landscape: Moose, WY, Grand Teton History Association in cooperation with the National Park Service, 132 p. 4) Pierce, K.L., and Good, J.D., 1992, Field Guide to the Quaternary Geology of Jackson 4,5 Hole, Wyoming: United States Geological Survey Open-File Report 92–504, 59 p. 5) Pierce, K.L., Licciardi, J.M., Good, J.M., and Jaworowski, C., 2018, Pleistocene Glaciation of the Jackson Hole Area, Wyoming: U.S. Geological Survey landforms which are offset by faulting . Professional Paper 1835: U.S. Geological Survey Professional Paper 1835, 68 p. 6) Amos, C.B., Kelson, K.I., Rood, D.H., Simpson, D.T., and Rose, R.S., 2010, Late Quaternary slip rate on the Kern Canyon fault at Soda Spring, Tulare County, California: Lithosphere, v. 2, p. 411–417, doi:10.1130/L100.1. 7) McCalpin, J.P. (Ed.), 1996, Paleoseismology: San Diego, California, Academic Press, 588 p. 8) Thompson, S.C., Weldon, R.J., Rubin, C.M., Abdrakhmatov, K., Molnar, P., and Berger, G.W., 2002, Late Quaternary slip rates across the central Tien Shan, Kyrgyzstan, central Asia: SLIP RATES ACROSS THE KYRGYZ TIEN SHAN: Journal of Geophysical Research: Solid Earth, v. 107, p. ETG 7-1-ETG 7-32, doi:10.1029/2001JB000596. 9) Figure 1. Study area. Teton fault in red. Figure 4. VS along the Teton fault and four-period moving average trend line Figure 3. Comparison of scarps mapped by this investigation Zellman, M., DuRoss, C., and Thackray, G., 2019, The Teton Fault Teton County, Wyoming: Wyoming Geological Survey Open File Report 2019–1, 1 p. 10) Cowie, P.A., and Roberts, G.P., 2001, Constraining slip rates and spacings for active normal faults: Journal of Structural Geology, v. 23, p. 1901–1915, doi:10.1016/S0191-8141(01)00036-0. 11) Cowie, P.A., and Scholz, C.H., 1992, Growth of faults by accumulation of seismic slip: Journal of Geophysical Research, v. 97, p. 11085, (dashes) to highlight observed patterns. Colors correspond to those in Figure 5. and those of Zellman et al. (2019). doi:10.1029/92JB00586. 12) Densmore, A.L., Gupta, S., Allen, P.A., and Dawers, N.H., 2007, Transient landscapes at fault tips: Journal of Geophysical Research, v. 112, p. F03S08, doi:10.1029/2006JF000560. SUPPORT: This project was funded by NSF grant 1755079 to ISU (PI Thackray). Additional support was provided by the University of Wyoming National Park Service and Idaho State University Career Path Internship program..
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