EGU2020-20580
https://doi.org/10.5194/egusphere-egu2020-20580
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Transfer of displacement between faults of opposed dip

Conrad Childs1,2, Robert Worthington3, John Walsh1,2, and Vincent Roche1,2
Conrad Childs et al.
  • 1UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4.
  • 2iCRAG (Irish Centre for Research in Applied Geosciences), UCD School of Earth Sciences, University College Dublin
  • 3Equinor, Sandsliveien 90, 5254, Bergen, Norway

The transfer of displacement between faults that dip in the same direction is well understood and relay ramps between adjacent fault segments have been frequently described. Perhaps counterintuitively, displacement can also be transferred between faults that dip in opposite directions but the structure at the boundaries between opposed dipping faults is not well understood. We constrain the mechanism by which displacement is transferred between opposed-dipping faults by examining the geometries of faulted horizons and fault throw distributions at these ‘conjugate relay zones’.

Structure contour maps of horizons offset by overlapping opposed-dipping faults from different extensional settings display a consistent pattern. Above the line of intersection between the conjugate faults the deformed horizon is flat between converging faults and displacement transfer is reflected in changes in footwall elevation. Below the line of fault intersection the mutual footwall is flat and elevation changes occur in the hanging walls of the divergent faults. These elevation changes can be explained as a simple superposition of the deformation fields of two faults that have retarded lateral propagation due to the presence of the other synchronous fault, irrespective of whether the two faults actually intersect. The observed patterns of horizon elevation strongly resemble those seen at boundaries between adjacent basin-scale half-graben of opposed polarity.

How to cite: Childs, C., Worthington, R., Walsh, J., and Roche, V.: Transfer of displacement between faults of opposed dip, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20580, https://doi.org/10.5194/egusphere-egu2020-20580, 2020

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Presentation version 1 – uploaded on 01 May 2020
  • CC1: Comment on EGU2020-20580, Christopher Jackson, 04 May 2020

    Hi Conrad! 👋🏾 Very nice work, which I think I saw Rob present some of at TSG last year. Beyond the finite 3D strain, do you have a sense as to how slip is progressively accumulated on conjugate faults such as these? Are any associated with growth strata? Or did they grow only as blind structures? Thanks! Chris Jackson (Imperial College)

    • AC1: Reply to CC1, Conrad Childs, 04 May 2020

      Hi Chris,

      Thanks for the comment. As far as we can see the slip accumulates in the same way as for relay zones between faults with the same dip direction. The big difference of course is that they can’t breach. We have looked only at places where the conjugate relays are between segments within arrays at fairly low strains. I am not sure what will happen as strain continues to increase – is one of the faults bypassed or does the fault just lock-up. I have one example where it looks from growth strata that one of the conjugates propagates and the other retreats.

      Yes, you can have conjugate relay zones between faults that intersect the free surface. Slide 17 in the presentation shows two examples of this. The neat thing about the example on the right is that the faults dip away from one another demonstrating that the high displacement gradients are the result of interaction between the fault deformation fields rather than because the fault surfaces intersect one another. We suggest that the geometries we describe for the small faults we concentrate on may also be relevant for large, basin-bounding, faults.

      Conrad