Strain compatibility and fault linkage in relay zones on normal faults |
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| Institution: | 1. Department of Earth Sciences, Durham University, Durham, UK;2. Geospatial Research Ltd., Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;1. Department of Electrical Engineering, National Institute of Technology, Raipur 492010, Chhattisgarh, India;2. Department of Electrical Engineering, University of Sharjah, United Arab Emirates;1. 5726 Overlook Ave NE, Tacoma, WA 98422, USA;2. Department of Earth & Environmental Sciences, University of Rochester, Rochester, NY 14627, USA;1. CNRS/INSU, ISTO, UMR7327, 45071 Orléans, France;2. Université d''Orléans, ISTO, UMR7327, 45071 Orléans, France;3. Total SA, Structural Geology Department, CSTJF, 64000 Pau, France |
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| Abstract: | Relay zones on normal faults are unlikely to have tabular geometries as depicted in idealised models. Rotation of a relay ramp between non-parallel and non-planar relay-bounding faults will inevitably lead to strain compatibility problems causing open gaps or overlaps within the relay zone. Linkage of relay-bounding faults does not evolve from a single branch point. Rather, linkage occurs at multiple points along the fault tip lines giving rise to initially discontinuous branch lines. Where linkage occurs along a discontinuous slip-aligned branch line, displacement at different levels within the relay zone is partitioned between variable amounts of ramp rotation and slip across the branch line. The linking fault propagates when strain compatibility can no longer be maintained by continuous deformation processes, such as thickening or thinning of incompetent layers within the relay ramp. Step-like changes in vertical displacement vs. distance (d − x) profiles on horizons containing apparently intact relay ramps are probably indicative of incipient breaching and can be used predict the presence of a slip-aligned branch line in the sub-surface. Despite the complexity of the strain distribution within relay zones, the total vertical displacement across the relay remains geometrically coherent at all levels. |
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