Understanding seismic anisotropy in the Rotondo granite: investigating stress as a potential source

Behnen, Kathrin; Hertrich, Marian; Maurer, Hansruedi; Shakas, Alexis; Bröker, Kai; Epiney, Claire; Blanch Jover, María; Giardini, Domenico

doi:https://doi.org/10.5194/se-16-333-2025

Articles | Volume 16, issue 4/5

https://doi.org/10.5194/se-16-333-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/se-16-333-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 4/5

Research article

|

15 May 2025

Research article |

| 15 May 2025

Understanding seismic anisotropy in the Rotondo granite: investigating stress as a potential source

Kathrin Behnen, Marian Hertrich, Hansruedi Maurer, Alexis Shakas, Kai Bröker, Claire Epiney, María Blanch Jover, and Domenico Giardini

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Final revised paper (published on 15 May 2025)
Preprint (discussion started on 22 Aug 2024)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-1919', Wojciech Gajek, 07 Oct 2024

The paper discusses the hypothetic impact of stress-induced anisotropy on the velocity of seismic waves. Importantly, the analysis addresses the igneous type of rocks and includes a simple yet directly addressing problem case study with good-quality data. This unique case study examines stress-induced anisotropy due to the impact of overburden stress on igneous rocks in an in-situ condition that falls between reservoir and lab scales.

The paper is well-written, clearly presents the data and contains a comprehensive discussion. The paper may have been better if it contained: a wider picture of stress-induced anisotropy in the introduction together with a more complete discussion of previous and similar works in stress-induced anisotropy topic. Also, Authors should carefully revise the text to eliminate phrases like "slightly better" and eliminate typos. A nice addition, that might have been used by the Authors in future is including fractures in the inversion of the stiffness tensor for more complete inversion.

Nevertheless, according to the provided discussion, the presented material is sufficient for drawing presented conclusions. However, one the cited materials (namely "Schneider, C.: Seismic Velocity Anisotropy and Microstructural Characterization of Ductile Shear Zones in the Rotondo Granite, Ph.D. thesis, 2022." ), to my understanding is the only and crucial source to verify the claims of the Authors regarding the absence of intrinsic anisotropy in discussed rocks: "The undeformed Rotondo granite is also fully isotropic under high pressures in the lab, indicating that the anisotropy is not intrinsic from the material itself but must be controlled by external factors (Schneider, 2022)." Unfortunately, despite my attempts, I was unable to find this publication (thesis) to verify the claims above.
Therefore, I would recommend this paper undergo a minor revision, during which I would require the Authors to update the reference to be complete (including e.g. a link to university repository) to the cited thesis that would be in agreement with Solid Earth's recommendations on citing theses, as a condition to be accepted. Alternatively, Authors should provide another reasoning (e.g., a modified figure from that thesis if possible) showcasing a lack of intrinsic anisotropy. Without these, the results is too speculative to be published in current form.

Some specific comments, corrections etc are included in the annotated pdf.

Citation: https://doi.org/10.5194/egusphere-2024-1919-RC1
- AC2: 'Reply on RC1', Kathrin Behnen, 11 Dec 2024
  
  Thank you for your detailed and constructive feedback on the manuscript. Your comments are greatly appreciated and will definitely help to further improve the paper. We understand your concerns that the paper should include a wider picture of stress-induced anisotropy and lacks the comparison with other studies on this topic. We will revise the introduction and discussion section to incorporate relevant studies.
  We also highly appreciate your comment, to include fractures in the inversion of the stiffness tensor. You are right that this could lead to a more complete inversion. We will keep this in mind for further studies on this topic.
  Thank you for indicating that the work of Schneider et al. (2022) is not available online. You are right that the material you mentioned is essential for the analysis of the intrinsic anisotropy of the Rotondo granite analyzed in this study. It’s the only work so far, measuring seismic anisotropy under controlled conditions in the lab for different (confining) pressures.
  The thesis is submitted to the research collection of ETH Zurich and will be available soon. The DOI will then be added to the revised manuscript. Unfortunately, there is a mistake in the reference list of the manuscript, it’s not a PhD thesis but a master thesis. We will of course correct this and I’m very sorry for this mistake.
  We also appreciate your comments and correction in the manuscript itself. Responses to the comments are directly included in the attached pdf.
  
  Citation: https://doi.org/10.5194/egusphere-2024-1919-AC2
RC2:
'Comment on egusphere-2024-1919', Leon Thomsen, 03 Nov 2024

See attached file

Citation: https://doi.org/10.5194/egusphere-2024-1919-RC2
- AC1: 'Reply on RC2', Kathrin Behnen, 11 Dec 2024
  
  Thank you for the constructive feedback and detailed comments, which will certainly help to improve the manuscript. In the attached pdf we provide detailed responses to each of the points raised by you.
  
  Citation: https://doi.org/10.5194/egusphere-2024-1919-AC1

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Kathrin Behnen on behalf of the Authors (23 Jan 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (26 Jan 2025) by Michal Malinowski

RR by Leon Thomsen (19 Feb 2025)

ED: Publish as is (01 Mar 2025) by Michal Malinowski

ED: Publish as is (01 Mar 2025) by CharLotte Krawczyk (Executive editor)

AR by Kathrin Behnen on behalf of the Authors (03 Mar 2025)

Short summary

Several cross-hole seismic surveys in the undisturbed Rotondo granite are used to analyze the seismic anisotropy in the Bedretto Lab, Switzerland. The P and S1 waves show a clear trend of faster velocities in the NE–SW direction and slower velocities perpendicular to it, indicating a tilted transverse isotropic velocity model. The symmetry plane is mostly aligned with the direction of maximum stress, but also the orientation of fractures is expected to influence the velocities.