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Releasing bends along active strike-slip faults display a range of fault patterns that may depend on crustal strength. Scaled physical experiments allow us to directly document the evolution of established releasing bend systems under differing strength conditions. Here, we use a split-box apparatus filled with wet clay of differing strengths to run and analyze releasing bend evolution. Precut vertical discontinuities within the clay slip with right-lateral displacement of the basal plate followed by the development of oblique-slip secondary faults. In contrast to the weaker clay experiment, which produces left-lateral cross faults that facilitate major reorganization of the primary slip pathway, the stronger clay experiment produces negligible cross faults and has a persistent primary slip pathway. Within both experiments, the dip of initially vertical faults shallows due to lateral flow at depth and left-lateral slip develops along normal fault segments that have highly oblique strike. The experiments show that fault systems within weaker strength materials produce greater delocalization of faulting, with both greater number of faults and greater off-fault deformation that can impact hazard. For example, the hot, thin and weak crust hosting the Brawley Seismic Zone accommodates slip along many distributed faults, which is in sharp contrast to the more localized fault network of the Southern Gar Basin in cooler, thicker and stronger crust. The fault patterns observed in the experiments match patterns of crustal examples and may guide future models of fault evolution within relatively strong and weak crust that have differing heat flux and thickness.
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Non-steady-state slip rates emerge along evolving restraining bends under constant loading
Recent field studies provide evidence of fault slip-rate variability over time periods of 10–100 k.y., yet researchers do not know how processes internal to the fault system (e.g., fault reorganization) impact records of fault slip rates. In this study, we directly observed fault-system evolution and measured slip-rate histories within a scaled physical experiment of a dextral strike-slip 15° restraining bend representative of a gentle crustal restraining bend. To assess the degree of slip-rate variability at particular sites along the experimental faults, such as would be revealed in a field study, we tracked fault slip rates at specific locations that advected throughout the experiment with accrued fault slip. Slip rates increased or decreased (5%–25% of the applied velocity) both during fault reorganization (e.g., fault growth and abandonment) and as sites migrated to new structural positions. Sites that advected into the restraining bend showed decreased slip rate. While we expect new fault growth to reduce slip rates along nearby fault segments, we document that the growth of new oblique-slip faults can increase strike-slip rates on nearby fault segments. New oblique-slip thrust faults within the experiment accommodated off-fault convergence and unclamped nearby strike-slip segments. The experimental results show that even under a constant loading rate, slip rates at sites located on stable fault segments can vary due to either reorganization elsewhere in the fault system or site advection.
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- Award ID(s):
- 2040570
- PAR ID:
- 10317064
- Date Published:
- Journal Name:
- Geology
- ISSN:
- 0091-7613
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1130/G49745.1
