3D geometry and displacement transfer of an oblique relay zone on outcropping normal faults

Relay zones on normal faults accommodate transfer of displacement between adjacent fault segments. We study vertical and horizontal displacement transfer mechanisms across a relay zone adjacent to the Moab Fault at Courthouse Rock (Utah, USA). The relay zone has a reservoir scale (map overlap length ca. 750 m, separation ca. 150 m), and is bounded by two normal fault segments with maximum throw of ca. 12 m. The relay zone is exposed on multiple, sub-parallel cliff faces and intervening rock pavements. We use photogrammetry of these exposures to build a 3D virtual outcrop model of the relay-bounding faults, subordinate faults deforming the relay zone and seven faulted stratigraphic horizons. The relay-bounding faults are right-stepping in map view and contractional in cross-section, defining a relay zone oblique to bedding in 3D. Displacement is transferred both horizontally and vertically across the relay zone. Horizontal transfer of displacement is achieved by a shallow dipping (<1(degrees)) relay ramp, whereas vertical transfer is achieved by antithetic faults within the relay ramp. Our analysis demonstrates that multiple mechanisms can work in conjunction to facilitate transfer of displacement across individual relay zones.

Automated summary

This study investigates the vertical and horizontal displacement transfer mechanisms across a relay zone adjacent to the Moab Fault. Photogrammetry and 3D modeling techniques were used to analyze the relay-bounding faults and subordinate faults within the relay zone. It was found that horizontal displacement transfer occurs through a shallow dipping relay ramp, while vertical displacement transfer is facilitated by antithetic faults within the relay ramp.