Net Slip and Linkage Patterns of the Sevier-Toroweap Fault System Terrance Delisser, and Amanda Hughes University of Arizona, Department of Geosciences

ABSTRACT Stratigraphy Methods Fault Linkage Example The Sevier-Toroweap fault system is a 250+ km long high angle normal Along-Strike Stratigraphic Cross section construction and net slip calculation: fault located in the High Plateaus subprovince on the southwest margin of the Correlation Chart of the Cross sections through the fault trace were made in the structural Here is a prominent Colorado Plateau region. This fault system alongside other Basin and Range style Sevier-Toroweap Fault System interpretation software MOVE to directly measure net slip. Measured net slip case of hard linkage along B’ normal faults structurally make up the Utah Transition Zone. As with all faults in the values, along with reported net slip values from literature, were used to develop the Sevier-Toroweap Fault An understanding of the B Transition Zone, the Sevier-Toroweap fault system trends N-S but has distinct displacement vs. distance plots for the Sevier-Toroweap fault system which will system. Net slip calculations regional stratigraphy will allow bends in the fault trace that trend northwest or northeast. These characteristic reveal linkage patterns. for cross section B-B’ (Figure changes in strike provide insight into the linkage history and segmentation of the for the estimation of slip 6) were done to supplement fault. Segmentation of the Sevier-Toroweap fault system involves the linkage of distribution of the Sevier- areas with limited reported individual short faults to form long faults. Since fault linkage history affects a fault Toroweap fault system. The system’s net slip distribution, characterizing the slip distribution along the Sevier- rock formations displaced by the Results displacement measurements. B’ Toroweap fault system reveals fault linkage history, which improves our The resulting displacement vs B fault system are Precambrian to Displacement data were compiled Meters distance plot helps reveal the 0 understanding of how this fault formed, its extent, and potential seismic hazards Tertiary in age and exhibit a from various sources (Figure 8) to associated with it. degree of linkage. In this variety of thickness trends as construct a displacement vs distance Cross-sections through displaced Paleozoic, Mesozoic, and Cenozoic case, these fault segments you move along strike (Figure 2). D D’ plot for the entire fault system (Figure 9). strata have been created using the structural interpretation software Move to linked recently as evidenced 1500 From the plot, two main linkage zones calculate displacement along the main trace of the fault system. Measured by low displacement rates Figure 6: Cross section construction for were identified connecting three main prominent hard linkage zone. Cross displacement values from theses cross sections were integrated with those from and the two displacement published USGS cross sections and other literature to produce plots of distance Northern segments (Figures 8 & 9). These linkage section location is displayed in Figure 1. maxima. vs. displacement along the full strike extent of the fault. These plots help Segment zones correspond with prominent hard Top inset from (Billingsley et al., 2008) demonstrate the segmentation and linkage history of the Sevier-Toroweap fault linked segments along the fault trace. Displacment Vs Distance Plot of Main Fault Trace (Sevier/Toroweap Merge) system and help reduce uncertainty as to where the northern terminus of the fault C C’ The southern segment has a maximum system lies. Initial estimates suggest that the northern terminus may extend as far Central displacement of 410m. It’s northern 100 as 100 km north of the northernmost visible trace of the fault system beneath the Segment linkage zone has net displacement 0 Marysvale Volcanic Field where it is thought to be buried. 103 105 107 109 111 113 115 B B’ values near zero suggesting this linkage Distance (km)

was recent. On the other hand, the Main Fault Trace (Sevier Segment) Western Segment-Little Hurricane Ridge

central segment, which has a max (m) slip Net Displacement/ Net Slip-Little Hurricane Ridge Linkage Zone Southern Location Map Segment displacement of 805m has an older Figure 7: Corresponding distance vs displacement plot Figure 2: Stratigraphic correlation chart of displaced formations along the strike of the Sevier-Toroweap fault northern linkage zone with higher A A’ Figure 1: Regional map of the system. The locations of columns C1 – C9 are indicated in Figure 1. displacement values around 400 m. The C8 Sevier-Toroweap Fault system northern linkage zone of the northern A A’ Conclusions and other major normal faults segment is not apparent on the plot but apart of the Basin and Range – Marysvale and may be located farther north based • Through the analysis of net slip distribution across the Sevier- Colorado Plateau transition Volcanic Field on its apparent max displacement of Toroweap Fault system, multiple segments and linkage zones were zone. Dashed lines indicate fault Fault Linkage Theory Figure 8: Data compilation of offset values ?? measured from this study and reported 1470m near the traceable extent of the identified with their relative timing of linkage. section boundaries. Square Isolated underlapping segments symbols represent the locations C9 from literature. fault. Panguitch of stratigraphic columns from the • The length of the northern identified segment was approximated t1 Displacment Vs Distance Plot of the Sevier-Toroweap Fault System allowing for an estimation of the northern extent of the fault as it’s correlation chart in Figure 2. D D’ Overlapping soft-linked segments S N Cross section B-B’ is shown in C8 1500 interacting with the Marysvale Volcanic Field. Relay Ramp Central Figure 6. The inset shows the Sevier Southern Segment Northern Segment 1000 Segment regional map in relation to major Section Future Work Hard-linked segments newly breached relay ramp 500 physiographic provinces in C7 Kanab UTAH t2 0 • Developing further cross sections to identify small scale linkage Arizona and Utah (BR, Basin and C C’ ARIZONA Cross fault Relay Ramp C6 0 50 100 150 200 250 patterns Range; CP, Colorado Plateau; Northern Toroweap Hard-linked segments with adjusted displacement profile Distance (km) C5

MRM; Middle Rocky Mountains). Displacement/ (m) slip Net • Creating a 3D model of the Sevier-Toroweap fault system which will B’ Main Fault Trace Western Segment-Little Hurricane Ridge B Figure significantly modified after Western Segement-Moccasin Monocline Net Slip-Little Hurricane Ridge Linkage Zone be used to determine different earthquake hazard slip scenarios Lund and others, (2008). C4 Net Slip-Moccasin Monocline Linkage Zone Marysvale Volcanic Field t3 boundary after Best and others, C3 Central Toroweap Figure 9: Displacement vs distance plot for the Sevier Toroweap Fault system revealing (2013). A A’ multiple potential segment boundaries. C2 References Southern Toroweap Further investigation was C1 Best, M. G., Christiansen, E. H., & Gromme, S. (2013). Introduction: The 36–18 Ma southern conducted to determine the length of Great Basin, USA, ignimbrite province and flareup: Swarms of subduction-related t the northern segment. It is known that supervolcanoes. Geosphere, 9(2), 260-274. The Sevier-Toroweap fault system is a long geometrically segmented fault 4 the maximum displacement is typically Biek, R.F., Rowley, P.D., Anderson, J.J., Maldonado, F., Moore, D.W., Hacker, D.B., Eaton, J.G., system apart of the Basin and Range-Colorado Plateau Transition Zone (Figure Hereford, R., Filkorn, H.F., and Matyjasik, B., 2014, Geologic map of the Panguitch 30′ x 60′ 1). It consists of four traceable sections in northwestern Arizona and southwestern located halfway along a fault segment. quadrangle, Garfield, Iron, and Kane Counties, Utah: Utah Geological Survey Map, 4 plates, scale 1:62,500 (in press). Utah before disappearing in the Miocene Marysvale Volcanic Field. The The expected length of the northern Figure 4: Collection of diagrams displaying the stages of fault linkage with corresponding plot of Billingsley, G. H., Block, D. L., & Dyer, H. C. (2006). Geologic Map of the Peach Springs 30ʹ X 60ʹ segmentation of this fault system, implied by strike changes, occurs from the fault segment is ~166 km based on the Quadrangle, Mohave and Coconino Counties, Northwestern Arizona. “Displacement vs. Horizontal distance along faults” showing displacement distributions for each stage. linkage of short normal faults and is revealed through it’s net slip distribution. 83 km half length to the apparent Billingsley, G. H., Priest, S. S., & Felger, T. J. (2008). Geologic Map of the Fredonia 30'X Figures slightly modified from Fossen, (2016). 60'quadrangle, Mohave and Coconino Counties, Northern Arizona. USGS. maximum. Plotting the expected length Billingsley, G. H., & Wellmeyer, J. L. (2003). Geologic Map of the Mount Trumbull 30'X An understanding of the stages of fault linkage and the merging of individual displacement profiles and displacement on a displacement 60'Quadrangle, Mohave and Coconino Counties, Northwestern Arizona (No. 2766). US (t1 – t4 in Figure 4) is necessary to properly characterize net slip distribution. Two isolated underlapping Geological Survey. Purpose length diagram gives us a reasonable Doelling, H. H. (2008). Geologic map of the Kanab 30’x 60’quadrangle. Kane and Washington but interacting faults (t1) will soft-link overtime (t2) to form a relay ramp structure. As deformation correlation. It is expected that the fault counties, Utah, and Coconino and Mohave counties, Arizona: Utah Geological Survey Miscellaneous Publications. • Characterize the fault linkage history of the Sevier-Toroweap Fault System continues, a cross fault will form, hard linking the fault segments and breaching the relay ramp (t3). With continues upwards of 80 km past the increased displacement, the displacement profile will eventually smoothen into one elliptical curve Doelling, H. H., Davis, F. D., & Brandt, C. J. (1989). The geology of Kane County, Utah: Geology, using net slip distribution which will inform us of how the fault system formed northern extent that is typically traced mineral resources, geologic hazards (Vol. 124). Utah Geological Survey. and potential seismic hazard associated with it. characteristic of a single fault (t4). What remains is a is a geometric bend and damage zone. With this Figure 10: Displacement vs length diagram Fossen, H. (2016). Structural geology. Cambridge University Press. understanding, characterizing the net slip distribution along the geometrically segmented Sevier- for this fault system which would place Lund, W. R., Knudsen, T. R., & Vice, G. S. (2008). Paleoseismic reconnaissance of the Sevier • Evaluate the northern extent of the fault system as it interacts with the for faults with the expected length of the Toroweap fault will reveal fault linkage patterns. the terminus 40+ km within the fault, Kane and Garfield counties, Utah (Vol. 122). Utah Geological Survey. Marysvale Volcanic Field northern segment plotted with a star. Figure Schiefelbein, I. M. (2002). Fault segmentation, fault linkage, and hazards along the Sevier fault, slightly modified from Fossen 2016. Marysvale Volcanic Field. southwestern Utah.