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| 22 Jul 2026
Modelling the interactions of discrete inherited structures, pervasive fabrics and extension direction during rifting: application to the Cenozoic Eger Graben
Abstract. Pre-existing mechanical heterogeneities significantly influence the evolution of continental rifts and their resulting fault architecture. The Cenozoic Eger Graben (EG) in the northwestern Bohemian Massif (Central Europe) represents a fossil rift system in which the role of structural inheritance has been relatively unaddressed. This study examines how basement structures inherited primarily from Paleozoic geodynamic events may have controlled syn-rift fault development in a setting where the orientation of the rift axis and basement fabric varied in space relative to the extension direction. Two series of crustal-scale analogue models inspired by the EG setting were designed to investigate the effects of both discrete and pervasive weaknesses on evolving fault populations. The first series simulated reactivation of a segmented basement weakness (velocity discontinuity, VD) under uniform or changing extension directions, testing an existing two-phase extension model. The second employed a uniformly extending elastic model base and approximated the role of pervasive fabrics by imprinting grooved patterns into the basal silicone layer. Surface strain evolution was analysed using digital image correlation, while final fault patterns were compared with the generalised structure of the EG. The results highlight the dominant influence of the initial extension phase during polyphase rifting, with the segmented geometry of the VD exerting further control on fault development. Some two-phase scenarios reproduce the observed fault pattern more successfully than others, suggesting that temporal variations in paleostress orientation remain plausible. However, experiments involving spatially variable basement fabrics demonstrate that faults of contrasting orientation and geometry can develop simultaneously above suitable inherited structures. Several structural features of the Eger Graben may therefore reflect synchronous reactivation of different inherited structures rather than rotation of the extension direction. The influence of pervasive fabrics on modelled fault geometries compares well with natural examples and demonstrates the broader applicability of this experimental approach.
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Status: open (until 05 Sep 2026)
- RC1: 'Comment on egusphere-2026-4246', Daniele Maestrelli, 26 Aug 2026 reply
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RC2: 'Comment on egusphere-2026-4246', Anonymous Referee #2, 01 Sep 2026
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Review of the paper “Modelling the interactions of discrete inherited structures, pervasive fabrics and extension direction during rifting: application to the Cenozoic Eger Graben” by Havlícek et al
Sept 2026
The papers use different series of analogue models to analyse the importance of inherited discrete and pervasive fabrics during rifting, in conditions of uniform or two-phase extension. The models are run both with the use of a discrete VD and basal foam to reproduce extension, and investigate different geometries of the fabrics. Results are used to analyze the influence of tectonic inheritance in the deformation architecture of the Egen Graben.
In general, the experiments are nice and well illustrated, but I found many different problems in this work –listed below- and I think that major revisions are needed before the manuscript can be considered further.
My main concern is related to the fact that the Authors put together many series of different experiments, with many different starting boundary conditions (e.g. experimental expedients to reproduce fabrics, different model domains, etc.) and different scaling relations which make the paper and the results not easy to follow. My feeling is that putting so (too) many things together may somehow reduce the impact of this paper, as some interesting results may be dispersed among many other less interesting ones. For instance, one could have split this work in two different papers: one (with the VD setup) dealing with the kinematics of deformation, geometry of the VD and resulting fault pattern, comparing this with nature at a basin scale; another one with the many experiment dealing with the different orientation, distribution, etc of inherited fabrics, comparing them with the characteristics of single faults or fault arrays in nature. This latter could have dealt with many aspects related to fault reactivation (e.g., pattern of fault growth and displacement/length profiles in case of reactivated fabric, kinematics of reactivated faults – see annotated pdf) which are currently not so much investigated. However, at this point, it is rather difficult to rearrange things this way.
Some of the sections of the paper are too long and could be maybe shortened. I refer for instance to section 2.1 and the too much information reported for the pre-Cenozoic history of the Eger Graben, which is not always strictly pertinent to the modelling. So, this section should be summarized and shortened, with only the information pertinent to the experiments left
Another important problem is that the Authors should provide a clearer definition of discrete vs pervasive fabrics: for instance, they can make use of Morley’s 1999 Journal of Structural Geology paper to clearly define them and refer to it. Also, a more detailed discussion of how the analogue fabrics transfer to natural conditions is to me important. For instance, as the Authors note, all these inherited fabrics do not strictly represent anisotropies in the brittle layer, as one could expect (and has been modelled in many other papers – see below); they simply reproduce spatial variation in integrated strength starting from lateral thickness variations or from the presence of a VD. How does this compare to nature? More localized deformation is expected when the fabric is reproduced within the brittle layer by –for instance- pre-cutting it and creating a strong internal anisotropy (see below).
Also, and very importantly, the use of a VD to simulate a discrete fabric may be appropriate, but the experimental series involving it investigates the kinematics of polyphase deformation not strictly the role of the fabric itself. Indeed, the series adopt a similar VD geometry and ‘simply’ changes the extension direction, not the characteristics of the VD. This is classic (‘old style’, I would say) approach in modelling, which has basically anything to do with the analysis of the characteristics of the discrete fabric/basal VD.
Moreover, placing a layer of viscous material on top of the VD surely complicates things, as this layer decouples (as the Author correctly indicate) the base of the model and the ‘discrete’ fabric from the uppermost brittle crust. As such, the viscous layer is redistributing deformation, which also depends on the applied strain rate and –according to this- may be localized or diffused. So, describing such a set-up in terms of discrete vs pervasive fabrics may be misleading and surely not straightforward.
Moreover, this initial boundary condition (i.e., presence of the decoupling viscous layer) is really confusing as the Authors admit that this layer is not present in nature. So, why has it been introduced? – I guess not to have a very localized deformation above the VD, but this has to be discussed more. Not really clear this point.
Limitations divided for the two series is again somehow confusing and go back to the previous point related to the split of the two different approaches/experiments/results. For the ductile layer (section 5.3) the Authors provide again a lot of details, which are at least in parts confusing: in general, the rheology does not seem to match that of the natural example, and this is the point. In one of these limitation sections (5.5) the Authors state “Due to the mechanically isotropic nature of granular materials such as quartz sand, modelling the effects of pervasive fabrics in commonly used rift sandbox setups has long been considered difficult to achieve and thus only a limited number of analogue studies exists (Chattopadhyay and Chakra, 2013; Morley, 1999; Samsu et al., 2021).”. This is actually incorrect as many papers (Bellahsen and Daniel, 2005 JSG; Corti et al., 2007; Zhou et al 2024 Tectonics, among others) have for instance used pre-cuts to model brittle inherited fabrics. As an alternative to cut, other papers (Wang et al., 2021) “pre-create” faults during a first deformation phase and analyse in detail their reactivation during a successive, non collinear phase of extension. Note that a comparison with the main findings from these previous papers is lacking in 5.4 and should be improved.
The comparison with nature is –at least for the experiments with VD- to me not convincing. Experiment E8, in its central part, is dominated by long, linear E-W faults; there are at least 5-6, 40cm-long E-W faults. But this is certainly not the case in nature, where the central parts is characterized by the presence of a few E-W fault segments (and there is only ‘major’ E-W highly segmented fault). So this pattern is to me more similar to experiment E13, where the central part is more segmented, although still characterized by E-W fault. Note that this latter also presents some WNW-ESE or NW-SE-trending minor fault segments, which may be somehow comparable to the similar fault set in nature. So, to me, the kinematics of experiment E13 more resembles nature than that of model E8. In any case the comparison is somehow confusing, highlighting portions of the natural rifts which compares to different portions of the models with difference kinematics, other portions which do not well resemble natural features, etc. So, the comparison is not straightforward at all.
And also the conclusions of the paper leave the reader with a sort of doubt and a sense of a lack of a main summary and integration between the two series (with or without VD) of experiments, see for instance lines 730-736 or 756-759. Has the direction of extension changed over time and are the VD experiments applicable and relevant? This is not very clear and somehow disappointing.
18 figures are to me too many – this is anyway related to the (too) many experiments and experimental approaches introduced in the paper, as described above
Data sets
Analogue modelling of the role of inherited structures in developement of the Eger Graben, Central Europe - dataset Filip Havlíček et al. https://doi.org/10.5281/zenodo.21397623
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Dear Editor, dear Authors,
I am here submitting my review comments for the manuscript entitled “Modelling the interactions of discrete inherited structures, pervasive fabrics and extension direction during rifting: application to the Cenozoic Eger Graben” by Filip Havlícek and co-authors.
This interesting manuscript deals with analogue modelling of rift settings and the interaction with inherited fabrics. The main aim of the models is to explain the present-day structural architecture (and the relationships with inherited fabrics) of the Eger Graben. The Authors produced 3 experimental series using 2 different setups, a first one using the classical VD approach to induce rifting under single- and multi-phase (oblique) extension, and a second one (using an expanding foam at the base) to test the effect of variously shaped fabrics in the crust, simulated via a preformed PDMS layer.
Overall, the manuscript is very well written and very well illustrated, even if the structure of the manuscript is sometimes redundant (e.g., Chapter 2 is long and very detailed, sometimes resembling more a thesis chapter, and could be shortened a bit; there are two limitations sections, one of which—5.3—could be easily incorporated into Section 5.2). Besides, the experimental series are well designed and monitored through the use of up-to-date PIV analysis and more classical line-drawing interpretation. Modelling results are very nice and nicely described.
I do have several comments (see below and the annotated version of the manuscript), but I think the manuscript deserves publication after minor/moderate revisions are accomplished. It presents interesting results and insights about fault reactivation, inheritance and, more specifically, about the structural setting and evolution of the Eger Graben. This will attract the interest of both the structural geology and analogue modelling communities, as well as researchers interested in studying the specific study area.
My main concerns are summarised as follows, but they are better detailed in the annotated PDF:
It has been a pleasure to review this interesting manuscript, and I look forward to seeing it published. Should the Authors need clarification about my comments, I am fully available to them.
Daniele Maestrelli