EGU2020-15764, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-15764
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Three-dimensional geometries of relay zones in normal faults

Giovanni Camanni1,2, Vincent Roche2,3, Conrad Childs2,3, Tom Manzocchi2,3, John Walsh2,3, John Conneally2,3, Muhammad Mudasar Saqab4, and Efstratios Delogkos2,3
Giovanni Camanni et al.
  • 1Università degli Studi di Napoli Federico II, Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse, Italy (giovanni.camanni@unina.it)
  • 2Fault Analysis Group, UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland
  • 3Irish Centre for Research in Applied Geosciences (iCRAG), UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland
  • 4Norwegian Geotechnical Institute, 40 St Georges Terrace, Perth, WA 6000, Australia

Individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation. Current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2D analysis from either maps or cross-sections observed in outcrop and, to a lesser extent, by the analysis of relay zones from 3D seismic reflection data. Using high quality 3D seismic reflection datasets from a selection of sedimentary basins, we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements (< ca. 190 m) which preserve the 3D geometry of 532 relay zones. Our analysis shows that relay zones most often develop by bifurcation from a single fault surface but can also arise from the formation of segments which are disconnected in 3D. Relay zones generally occur between fault segments that step in either the dip or strike direction, and oblique relay zones with an intermediate orientation are less frequent. This is attributed to the influence of mechanical stratigraphy, and to a tendency for faults to locally propagate laterally and vertically rather than obliquely. Cross-sectional stepping of relay zones typically forms contractional rather than extensional relay zones, a configuration which is attributed to the development of early stage Riedel shears associated with fault localisation. Comparing datasets from different geological settings suggests that the mechanical heterogeneity of the faulted sequence and the influence of pre-existing structure are the underlying controls on the geometrical characteristics of relay zones in normal faults, and different combinations of these two controls can account for the variation in fault zone structure observed between datasets.

How to cite: Camanni, G., Roche, V., Childs, C., Manzocchi, T., Walsh, J., Conneally, J., Saqab, M. M., and Delogkos, E.: Three-dimensional geometries of relay zones in normal faults, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15764, https://doi.org/10.5194/egusphere-egu2020-15764, 2020

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Presentation version 1 – uploaded on 20 Apr 2020
  • CC1: Comment on EGU2020-15764, Christopher Jackson, 04 May 2020

    Lovely work Giovanni! I can't access the paper from home, but did you use data from Taranaki? In that location, which I mention in our 'display', there are some very well-imaged segmented faults overlying (reactivated) pre-existing structures. They look similar to the top-right example in your conceptual models. Also, a recent paper of ours in Solid Earth, which John C reviewed, might be of interest in the context of segmentation associated with extensional growth folding. Chris Jackson (Imperial College)

    • AC1: Reply to CC1, Giovanni Camanni, 04 May 2020

      Hi Chris, thanks for your question. Yes, one of the datasets we used comprises faults that we mapped in the Taranaki Basin which look indeed very similar, in their 3D structure, to the faults shown in your “display”. However, the top-right example in our conceptual model refers to faults that developed in highly heterogeneous sequences, such as that of the Molasse Basin as described in the paper. Although the Taranaki Basin sequence is also associated with some mechanical contrasts among units, they are, to our knowledge, less accentuated than those in other areas and, therefore, the faults mapped in the Taranaki Basin would be more similar to those sketched in the bottom-right of our conceptual model (i.e., faults are downward physically linked to the pre-existing structure).

      • CC3: Reply to AC1, Christopher Jackson, 05 May 2020

        Thanks!

  • CC2: Comment on EGU2020-15764, Christopher Jackson, 04 May 2020

    Lovely work Giovanni! I can't access the paper from home, but did you use data from Taranaki? In that location, which I mention in our 'display', there are some very well-imaged segmented faults overlying (reactivated) pre-existing structures. They look similar to the top-right example in your conceptual models. Also, a recent paper of ours in Solid Earth, which John C reviewed, might be of interest in the context of segmentation associated with extensional growth folding. Chris Jackson (Imperial College)