the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Mar 2024
Selection and Characterisation of the Target Fault for Fluid-Induced Activation and Earthquake Rupture Experiments
Abstract. Performing stimulation experiments at approximately 1 km depth in the Bedretto Underground Laboratory for Geosciences and Geoenergies necessitates identifying and characterizing the target fault zone for on-fault monitoring of induced fault-slip and seismicity, a current challenge in understanding seismogenic processes. We discuss the multidisciplinary approach for selecting the target fault zone for the experiments planned within the Fault Activation and Earthquake Ruptures (FEAR) project, aiming to induce fault-slip and seismicity up to a magnitude 1.0 earthquake while enhancing monitoring and control of fluid-injection experiments.
Structural geological mapping, remote sensing, exploration drilling and borehole logging, ground-penetration radar, and laboratory investigations were employed to identify and characterize the target fault – a ductile-brittle shear zone several meters wide with intensely fractured volume persisting over 100 m. Its orientation in the in-situ stress field favors reactivation in normal to strike-slip regimes. Laboratory tests showed slight velocity strengthening of the fault gouge. The fault's architecture, typical for crystalline environments, poses challenges for fluid flow, necessitating detailed hydraulic and stress characterization before each of the FEAR experiments. This multidisciplinary approach was crucial for managing rock volume heterogeneity and understand implications for the dense monitoring network. Successfully identifying the fault sets the stage for seismic activation experiments commencing in spring 2024.
- Preprint
(11841 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on egusphere-2024-586', Richard Haslam, 12 Apr 2024
This paper bring together extensive characterization work undertaken at the BULGG in support of the FEAR project. The methodology and extent of characterization, as well as the rationale for fault selection is informative. There are clear citations to more specific aspects of the characterization.
- Does the paper address relevant scientific questions within the scope of SE? - YES
- Does the paper present novel concepts, ideas, tools, or data? - YES
- Are substantial conclusions reached? - Partially.
- Are the scientific methods and assumptions valid and clearly outlined? - YES
- Are the results sufficient to support the interpretations and conclusions? - YES
- Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? - The paper adequately points to more detailed papers on experiments.
- Do the authors give proper credit to related work and clearly indicate their own new/original contribution? - YES
- Does the title clearly reflect the contents of the paper? - YES
- Does the abstract provide a concise and complete summary? - YES
- Is the overall presentation well structured and clear? - YES
- Is the language fluent and precise? - YES
- Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? - Need to check notation for "E-20" etc. unsure if this should be in full with superscripts.
- Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? - Yes. These are noted in the attached PDF
- Are the number and quality of references appropriate? - YES
- Is the amount and quality of supplementary material appropriate? - N/A
Overall I enjoyed reviewing this paper and I am looking forward to seeing the results of the experiments.
Richard Haslam
-
RC2: 'Comment on egusphere-2024-586', Jamie Kirkpatrick, 26 Apr 2024
General Comments
This paper presents an overview of the work that has gone into identifying a target fault for the “FEAR” project in the Bedretto Underground Laboratory for Geosciences and Geoenergies. The paper is essentially a review and synthesis of previous work over the past few years documenting the structural and geomechanical environment of the BedrettoLab. There are two main contributions in the paper: 1. To describe in as much detail as possible the characteristics of the target fault for an injection experiment and relate those to potential seismic behavior, and 2. to outline the decision process for identifying the target fault and demonstrating how the information from the previous studies was interpreted and used to justify that decision. The first contribution is dealt with very well in the manuscript, but I think the authors could consider how they can use Discussion section of the paper to better inform the community about the relative value of the survey datasets to the decision-making process to make sure this is a paper that can be useful to a broad audience.
Overall, the scientific significance is excellent because this synthesis of data describing a fault structure is exceptionally detailed and the inferences drawn regarding the geometry and mechanical and hydrological properties will be tested with the planned injection experiment.
The scientific quality, is excellent. Much of the primary data has been reported previously, but the description of the methods and their uncertainties and treatment of those uncertainties in the interpretation is very good.
The presentation quality is also excellent. The paper is well written and the figures are generally high quality and useful. The text uses some jargon associated with the BedrettoLab project, which I suggest clarifying for a general audience (see minor comments below), but is mostly accessible.
- Does the paper address relevant scientific questions within the scope of SE? YES
- Does the paper present novel concepts, ideas, tools, or data? YES
- Are substantial conclusions reached? Yes, though as described above the conclusions may be more clearly described for a general audience
- Are the scientific methods and assumptions valid and clearly outlined? YES
- Are the results sufficient to support the interpretations and conclusions? YES
- Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? This is a review paper so the primary data is dealt with in the papers referenced in the work.
- Do the authors give proper credit to related work and clearly indicate their own new/original contribution? Yes, though the authors should consider how best to express their insights to a general audience in their contribution.
- Does the title clearly reflect the contents of the paper? YES
- Does the abstract provide a concise and complete summary? YES
- Is the overall presentation well structured and clear? YES
- Is the language fluent and precise? YES
- Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? Abbreviations need explaining in places
- Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? Minor clarifications suggested below. There are some sections that could be shortened without loss of content (Sections 1, 3, 6)
- Are the number and quality of references appropriate? YES
- Is the amount and quality of supplementary material appropriate? N/A
Specific Comments
Introduction mainly focuses on the scope of the FEAR project, but I suggest re-focusing some of the material in the second half of the introduction onto an explanation and justification for this study. Why is knowledge of the fault important? What fault characteristics are expected to be relevant and why?
It may be too late to reconsider this, but the name “FEAR” for a project that seeks to deliberately cause an earthquake is a potentially difficult choice for e.g. outreach and public awareness efforts.
Section 3: In point (1) Geometrical… have the authors been able to consider proximity to nearby faults in their list of fault properties? This is an important factor for mitigating potential triggering effects of a stimulated earthquake.
Section 5: I suggest the authors consider adding some detail of the degree of linkage of the different structures/sets/types as this could affect the total dimension of fault that may rupture. This is particularly important as the tip line of the MC fault has not been found so there is only a minimum bound estimate of the full dimension of the fault.
Line 114: can you include the slope of the tunnel (i.e. plunge) in this brief description of the tunnel attitude?
Line 126: Explain the terminology used for TM2805 etc. (what is the refrence frame for these values) – this could be done in the caption to Fig 1b.
Line 145: Check the figure calls here – type 2 structural orientations are in Fig 3k, whereas type3 orientations are in Fig 3j
Line 440: which side of the fault moved toward the SE?
Line 453: what is “BFE_A05” etc?
Line 497: why is the “anastomosing fault and fracture plane” geometry not shown in Fig 10?
Line 523: specify which elements of the approach specifically brought the most value so that future projects can benefit from these lessons.
Line 551: are the faults at 48 and 49 in figure 7 not principal slip planes? Is there any constraint on the offset across the MC fault?
Figure 1: Explain the contacts between rock types on the map in the legend or caption. Why are the traces of faults at the surface in B not shown in A also?
The MC fault is not defined in the text until Section 5.3, so references to MC fault in the captions to Figures 3, 4, 5 are confusing.
Citation: https://doi.org/10.5194/egusphere-2024-586-RC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 227 | 85 | 10 | 322 | 7 | 8 |
- HTML: 227
- PDF: 85
- XML: 10
- Total: 322
- BibTeX: 7
- EndNote: 8
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1