the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Sep 2025
The role of shear zones, faults and the associated fractures on the formation and character of bedrock surface depressions in crystalline bedrock (Turku, southwestern Finland)
Abstract. Surface morphology of the crystalline bedrock is controlled by brittle bedrock structures, and while the contribution of the large-scale structures such as shear zones and faults are acknowledged, the contribution of detailed brittle structures associated to large-scale structures is more often overlooked.
In this study, multi-scale analysis of brittle structures and detailed 3D-modelling provide improved knowledge how the detailed brittle structures contribute on the formation and character of the bedrock surface depressions.
While the shear zones, faults and elongated bedrock depressions show parallel trends and overlap, the outcrop-scale fractures largely determine the dimensions and detailed surface morphology of the bedrock depressions. The surface morphology and orientation of bedrock depressions along shear zones and faults are contrasting particularly due to the strong ductile precursor associated with the shear zones and their lack for faults. However, for both the shear zones and faults, localized brittle deformation controls the generation of outcrop-scale fracture, which further controls the detailed surface morphological signatures along the elongated bedrock depressions, and particularly in their damage zones.
This study provides new insights into the detailed bedrock structures, that contribute to the development of complex bedrock surface morphologies within the bedrock surface depressions which are controlled by the brittle deformation and kinematics along the underlying shear zones and faults.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-4271', Anonymous Referee #1, 18 Oct 2025
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RC2: 'Comment on egusphere-2025-4271', Anonymous Referee #2, 22 Oct 2025
The paper by Ruuska et al. proposes a study on how the network of shear zones, faults, and fractures influences the morphology of a crystalline basement. This topic is of particular interest as the Authors attempt to provide a detailed analysis of the spatial relationships between depressions and various types of tectonic structures. However, the paper requires significant work before it can be considered ready for potential publication. Firstly, the English language used is of mediocre quality, with sentence construction that is often clumsy and unclear. The text lacks fluency and it is frequently difficult to understand the Authors' intended meaning. A thorough revision of the text and how concepts are expressed is necessary. There are also many inadequacies in terminology choices, as highlighted in the attached PDF, which are prevalent throughout the work. The Abstract does not provide information on what was done, how it was done, or what results were obtained, appearing more like as a part of the Introduction.
Regarding the methods, it is not at all clear how field mapping was conducted, how foliations and fractures were classified, and there is no reference to classical methods for structural mapping in metamorphic rocks. The proposed high- and low-strain division seems arbitrary; it is unclear how it was determined and lacks a clear basis. To make this division meaningful, it is necessary to document the types of schistosity, mineral assemblage, and fabric through descriptions and images. Furthermore, there is a complete lack of information on how photogrammetric surveys were conducted, how 3D models (DOMs) were processed, and how fractures were mapped. As a result, the results and discussion sections are not grounded in well-documented data, suggesting a need to improve the presentation of results before revisiting discussions. More field images and more effective yet concise descriptions are needed. The discussions currently are verbose and not engaging; they should aim to get straight to the point. The influence of major shear zones and the F1 on the morphology is evident from the provided images. The impact of minor fractures is more questionable and requires better data presentation and documentation. The conclusions are not compelling for a broad audience of geoscientists and should be revised to highlight a broader significance beyond the local study. In summary, I suggest substantial revisions to make the paper presentable for a second review.
I would provide a constructive criticism aimed at improving the clarity, and impact of the paper, focusing on the clarity of language, methodology, and the presentation of results and discussion. I emphasize the importance of using standard geological terminology, including detailed descriptions of the methods used, and suggests improvements in how the findings are presented to engage a wider audience.
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The manuscript of Ruuska et al. uses novel, quantitative methodology for analysing deformed Proterozoic rocks and their glacial cover to better evaluate how these rock sequences may impact civil engineering/infrastructure projects. This work is especially important for northern Scandinavia as glacially eroded bedrock sequences are omnipresent.
The main goals of the manuscripts are well summarised in lines 74 to 77 in the Introduction. However, I would also emphasise the importance of the results for civil engineering/infrastructure purposes.
Here are my main points for improving the manuscript: