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Abstract Major normal fault systems are composed of segments that link as displacement accumulates, with linkage zone characteristics that reveal fault zone evolution. The steeply west-dipping Sevier fault zone in southwestern Utah, displays a complex fault network that developed between two long (>10 km), en echelon segments near the town of Orderville. Geologic map data and cross-sections of the transfer zone between the Mt. Carmel segment in the south and the Spencer Bench segment in the north reveal more than ten normal faults and four relay ramps displaying a range of geometries, including two relay ramps that display ramp-parallel folds. We suggest that transfer zone deformation was initially dominated by faults subparallel to the primary segments with later cross-faults that hard-linked these faults across most of the transfer zone. When the transfer zone was a soft-linked system, a displacement deficit likely existed relative to fault segments to the north and south. This early fault configuration would have reduced the efficiency of slip propagation associated with major earthquakes (>M7.0). In contrast, the present-day transfer zone, with a complex but hard-linked fault network, shows displacements that transition smoothly from the higher displacement (~800 m) southern segment to the lower displacement (~400 m) northern segment. That transition, combined with extensional strain within the zone, suggests that the Orderville fault network would be unlikely to impede propagation associated with future major earthquakes. The kinematic model of fault evolution presented here has implications for those investigating geothermal energy potential, groundwater flow, natural gas and oil reservoirs, mineral deposit formation, or seismic hazards. 

The segmented Sevier normal fault system displays a range of complex fault interactions that provide opportunity for researchers to learn about the different ways that fault segments interact and deform the rock around them. This article reviews the current state of research in the region and summarizes undergraduate student researchers' results from a 2022-2023 Keck Advanced Project; the project was supported by the Keck Geology Consortium and NSF grant 2042114, awarded to PI Ben Surpless. 

When faults propagate and accumulate displacement, they generate fracture networks that permit fluid flow. In this study, the authors performed 3D computer modeling of fault systems to test geothermal energy potential. 

The Sevier fault zone near Orderville, Utah, represents a segmented normal fault system within the transition zone between the Basin and Range Province and the Colorado Plateau. This fault system consists of three primary segments: the Orderville segment, the Spencer Bench segment, and the Mt. Carmel Segment. The interactions between segments led to the development of complex structural geometries exposed along the fault zone. These geometries influence deformation and create fractures that affect expected permeability and fluid flow within the fault zone. These geometries also impact how slip-related energy is dissipated during earthquake-related slip propagation. Therefore, analysis of these geometries has implications for f luid flow and seismic hazard within segmented fault systems. I used the Move2020 software suite by Petex to develop a 3D model of the complexly-segmented Sevier fault zone near the city of Orderville in southern Utah. Earlier researchers’ subsurface interpretations were based on surface mapping rather than direct documentation of subsurface fault and layer geometries, so 3D model development permits validation of hypothesized subsurface structures. I digitized geologic contacts, faults, and stratigraphic horizons based on published geologic mapping and cross-sections to develop a 3D model of the fault network. I confirmed that the model does represent a well-constrained 3D system of the Sevier fault zone based on demonstrated integrity between the digital elevation model (DEM), and all available structural data. This work should provide future researchers with the data necessary to model evolution of the overall fault system, which will permit accurate determination of fault-related fracture development and the most likely fluid flow paths. Furthermore, development of a fully retro-deformable model of the fault zone will allow strain analysis that may help researchers understand how fault segment geometries impact earthquake slip propagation. This determination can be used to provide a conceptual framework for other researchers to better constrain the evolution of segmented fault zones worldwide. 

Fault-tip damage zones develop in response to fault propagation and displacement and are caused by the local amplification of stresses at the fault tip. Understanding the geometry and intensity of damage zones is crucial for evaluating earthquake hazards and assessing the potentials of oil and gas production, geothermal energy, and groundwater resources. Fractures initiate as a result of stresses exceeding rock strength and propagate based on the stress field at the fault tip. We investigate the damage zone of a fault segment within the Sevier normal fault zone near Orderville, Utah, focusing on fractures that developed within the Jurassic Navajo Sandstone, the Temple Cap Formation, and the oldest beds of the Carmel Formation. Because normal faults grow laterally as slip and displacement increase, we focus on the tip zone of a fault segment where fracturing is well-exposed. We executed a series of unmanned aerial vehicle (UAV) flights to capture high-resolution imagery of inaccessible rock exposures. We use these images to construct structure-from-motion (SfM) virtual outcrop models (VOMs) that we georeference and analyze using Agisoft Metashape. We collected and analyzed fracture orientation and intensity data in the field and with VOMs. Both types of data reveal a distribution of fracture intensity that is consistent with inner and outer damage zones similar to previous studies of other fault systems. Adjacent to the tip, the inner damage zone has a higher fracture intensity on the hanging wall compared to the footwall. This high fracture intensity on the hanging wall ends 30 meters over from the fault core where the intensity of the outer damage zone of the hanging wall becomes similar to that within the inner damage zone of the footwall. Laterally, along strike of the fault tip, intense fracturing ends 60 meters to the south and all fracturing ends 350 meters from the fault tip. Our results have implications for the spatial distribution of fracturing and related permeability in similar normal fault systems.