Mechanisms and Mitigation of Injection-Induced Microseismicity: The Critical Role of Fracture Orientation in Shear Reactivation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript investigates microseismic mechanisms during hydraulic stimulation in Hot Dry Rock (HDR) geothermal systems using a 3D hydromechanical distinct element model. Results highlight that fractures oriented ~45° to maximum principal stress are most susceptible to clustering and larger seismic events. Microseismic magnitudes are governed by fracture orientation and fluid pressure, especially near injection wells. Cyclic injection shows limited benefit, while proppant diversion is proposed as a more effective mitigation strategy. The study provides insights for improving safety and efficiency in HDR geothermal exploitation.

Following  are my suggestions to improve the manuscript

1. The manuscript presents valuable modeling insights into microseismic mechanisms during hydraulic stimulation of Hot Dry Rock reservoirs. However, I recommend correcting the treatment of earthquake magnitude. All microseismic events generated in this study are below M 0.3 (very law), where the conventional Moment Magnitude Scale (Mw, Hanks & Kanamori, 1979) becomes unreliable. The Mw scale was mainly developed and validated for Southern California and is not universally applicable for small-to-moderate events worldwide; for global application, Mw is generally appropriate only for large to very large earthquakes (above ~M 7.5), as demonstrated in many studies (BSSA, Natural, Hazard, Applied Science). For microseismicity, it is more appropriate to use the Moment Magnitude for small-to-moderate events (Mwg), which has been specifically developed and validated for this magnitude range, providing a more accurate estimate of radiated seismic energy (see "A Seismic Moment Magnitude Scale", BSSA; "Limitations of Mw and M scale....", 2025). I strongly suggest replacing Mw with Mwg in calculations, figures, and terminology throughout the manuscript to ensure scientific accuracy and strengthen the interpretation of seismic risk.
2. The abstract concludes by recommending "proppant diversion." This term is somewhat vague in this context. Specify the intended mechanism. Do you mean using proppants to clog these critical fractures, thereby diverting fluid pressure to less sensitive fractures? Clarify this proposed mitigation strategy to make it more concrete and impactful.

3. Clarify the "Power-Law Distribution" Claim.  In Section 4.3 and Figure 13, you state the magnitude distribution obeys a power-law (Gutenberg-Richter) distribution. The histogram in Fig. 13a does not clearly show this. Consider adding a log plot of frequency versus magnitude to visually demonstrate the linear relationship that characterizes a power law. This would provide stronger evidence for your claim.

4. The recommendation to avoid high pressure in 45°-oriented fractures near the wellbore is sound but operationally challenging. In the Conclusion or Discussion, briefly discuss how this could be achieved in practice. 

5.  In Section 4.4, you note that cyclic injection produces more microseismic events but with a slightly lower maximum magnitude. Emphasize that seismic hazard is primarily driven by the largest events, not the total number. Therefore, a method that reduces the maximum magnitude (even marginally) might be preferable, despite the increase in total event count. This is a crucial point for risk assessment.

6.  Section 4.1.2 and Figure 10 introduce a 3D Mohr circle analysis, but the explanation is brief. For readers less familiar with this technique, add a sentence or two explaining how the 3D Mohr circle is used to identify the critical stress state for fractures of different orientations, and how this directly links to the Coulomb failure criterion you mention.

7. Discuss the Limitations of the Model More Explicitly. Add a dedicated subsection or paragraph discussing the model's limitations. Key points include: the simplification of the DFN; the assumption of impermeable rock matrix (justified but still a limitation); the use of a purely elastic model for the blocks, neglecting plastic deformation; and the fact that the calculated magnitudes are highly dependent on the mesh size, as noted in Section 2.2.

8. The manuscript uses "occurrence," "orientation," and "azimuth" somewhat interchangeably. Standardize the terminology. "Orientation" is a general term encompassing both "dip" and "dip direction" (or "strike"). Consistently using "orientation" or specifying "dip angle relative to σ1" would improve clarity.

9.  Some figures, like Figure 8 and Figure 15, are critical but could be improved. Ensure that the 7 microseismic planes in Figure 8 are clearly distinguishable, perhaps by using a more distinct color palette. In Figure 15, the schematic (h) should be larger and more clearly linked to the subplots (a-g). Adding a legend that explicitly maps colors to magnitude ranges in these plots would also be helpful.

 

Author Response

Responses to Reviewer #1

The manuscript investigates microseismic mechanisms during hydraulic stimulation in Hot Dry Rock (HDR) geothermal systems using a 3D hydromechanical distinct element model. Results highlight that fractures oriented ~45° to maximum principal stress are most susceptible to clustering and larger seismic events. Microseismic magnitudes are governed by fracture orientation and fluid pressure, especially near injection wells. Cyclic injection shows limited benefit, while proppant diversion is proposed as a more effective mitigation strategy. The study provides insights for improving safety and efficiency in HDR geothermal exploitation. Following are my suggestions to improve the manuscript.

Author response: Thanks for your constructive suggestions and positive comments. We have now revised the manuscript following your comments carefully. The modified parts have been marked in red in the manuscript. Below are point-by-point responses to your comments, indicating the page/line for each of the changes. The corresponding modifications and corrections were made and highlighted in the revised manuscript.

 

Comment 1. The manuscript presents valuable modeling insights into microseismic mechanisms during hydraulic stimulation of Hot Dry Rock reservoirs. However, I recommend correcting the treatment of earthquake magnitude. All microseismic events generated in this study are below M 0.3 (very law), where the conventional Moment Magnitude Scale (Mw, Hanks & Kanamori, 1979) becomes unreliable. The Mw scale was mainly developed and validated for Southern California and is not universally applicable for small-to-moderate events worldwide; for global application, Mw is generally appropriate only for large to very large earthquakes (above ~M 7.5), as demonstrated in many studies (BSSA, Natural, Hazard, Applied Science). For microseismicity, it is more appropriate to use the Moment Magnitude for small-to-moderate events (Mwg), which has been specifically developed and validated for this magnitude range, providing a more accurate estimate of radiated seismic energy (see "A Seismic Moment Magnitude Scale", BSSA; "Limitations of Mw and M scale....", 2025). I strongly suggest replacing Mw with Mwg in calculations, figures, and terminology throughout the manuscript to ensure scientific accuracy and strengthen the interpretation of seismic risk.

Author response: Thank you for your opinion. We have carefully readed the article about Mwg mentioned in your comment, and have attempted to modify the results. However, after comparison, the difference between the results before and after modification is very small (magnitude difference is less than 0.05, and the frequency and distribution has almost no effect). Besides, if all the models in the article are recalculated, it will take a lot of time (about two months) because the re-operation of the models. Considering that the moment magnitude Mw has been widely recognized and widely used for a long time, and on-site attention mainly uses the moment magnitude, the article still considers using the moment magnitude Mw for analysis. Although this may result in a difference of about 5-10% in the maximum magnitude, it has almost no impact on the overall analysis results (fracture mechanics processes within the formation). In addition, Mwg seems to have not been widely recognized by the academic community yet (As reference: “ Comment on "A Seismic Moment Magnitude Scale" by Ranjit Das, Mukat Lal Sharma, Hans Raj Wason, Deepankar Choudhury, and Gabriel Gonzalez”). Considering these factors, we still choose the traditional moment magnitude as the tool for earthquake analysis. But for the sake of completeness and objectivity, the article provides an explanation of Mwg, and we will also focus on using Mwg for analysis in future research.

 

Comment 2. The abstract concludes by recommending "proppant diversion." This term is somewhat vague in this context. Specify the intended mechanism. Do you mean using proppants to clog these critical fractures, thereby diverting fluid pressure to less sensitive fractures? Clarify this proposed mitigation strategy to make it more concrete and impactful.

Author response: Thank you for your opinion. “Proppant dispersion” refers to a special diversion technique that can to some extent control the injection of fluid in the designed direction and prevent fracturing fluid and proppants from flowing into certain fractures. Considering that this may lead to some misunderstandings, corresponding modifications have been made in the article in Page 1 Lines 27-29.

 

Comment 3. Clarify the "Power-Law Distribution" Claim. In Section 4.3 and Figure 13, you state the magnitude distribution obeys a power-law (Gutenberg-Richter) distribution. The histogram in Fig. 13a does not clearly show this. Consider adding a log plot of frequency versus magnitude to visually demonstrate the linear relationship that characterizes a power law. This would provide stronger evidence for your claim.

Author response: Thank you for the advice. The text has been revised and the figures have been redrawn in Page 17 Line 504.

 

Comment 4. The recommendation to avoid high pressure in 45°-oriented fractures near the wellbore is sound but operationally challenging. In the Conclusion or Discussion, briefly discuss how this could be achieved in practice.

Author response: The current fracturing technology can use directional perforation and fixed section sealing technology to achieve the sealing of specific well sections and prevent the injection of fracturing fluid. In addition, there are some temporary blocking techniques that can achieve temporary isolation of some cracks. The main focus of this study is to demonstrate the possibility of reducing the risk of microseismicity by reducing fluid pressure within fractures, without primarily discussing how this technology can be implemented. Although the sealing technology for cracks is still in the research and development stage, with the development of technology, sealing measures that can meet technical requirements will be established in the future.

The representative research on temporary sealing technology for cracks is as follows:

“Optimizing the selection of bridging particles for reservoir drilling fluids”；

“Study on the migration characteristics of temporary plugging agents in hot dry rock fractures considering ambient temperature field variations”；

The above explanations and references have been added to the article.

 

Comment 5. In Section 4.4, you note that cyclic injection produces more microseismic events but with a slightly lower maximum magnitude. Emphasize that seismic hazard is primarily driven by the largest events, not the total number. Therefore, a method that reduces the maximum magnitude (even marginally) might be preferable, despite the increase in total event count. This is a crucial point for risk assessment.

Author response: Thank you for your valuable advice. The analysis of the maximum magnitude has been added in section 4.4.

The total amount and scope are not only for earthquake risk analysis. In practical engineering, the number and spatial distribution of microseismic events also indirectly reflect the construction effect of reservoir fracture networks. A higher number of microseismic events represents more activated fractures, which helps analyze the activation effect of the reservoir.

 

Comment 6. Section 4.1.2 and Figure 10 introduce a 3D Mohr circle analysis, but the explanation is brief. For readers less familiar with this technique, add a sentence or two explaining how the 3D Mohr circle is used to identify the critical stress state for fractures of different orientations, and how this directly links to the Coulomb failure criterion you mention.

Author response: Thank you for pointing this out. As suggested by the reviewer, these explanations have been added to the article in Page 13 Lines 422-426.

 

Comment 7. Discuss the Limitations of the Model More Explicitly. Add a dedicated subsection or paragraph discussing the model's limitations. Key points include: the simplification of the DFN; the assumption of impermeable rock matrix (justified but still a limitation); the use of a purely elastic model for the blocks, neglecting plastic deformation; and the fact that the calculated magnitudes are highly dependent on the mesh size, as noted in Section 2.2.

Author response: Thank you for your valuable advice. As suggested by the reviewer, a description of the limitations of the model has been added to the article in Page 5 Lines 209-217.

 

Comment 8. The manuscript uses "occurrence," "orientation," and "azimuth" somewhat interchangeably. Standardize the terminology. "Orientation" is a general term encompassing both "dip" and "dip direction" (or "strike"). Consistently using "orientation" or specifying "dip angle relative to σ1" would improve clarity.

Author response: Thank you for pointing this out. The reviewer is correct. In this manuscript, “strike” means the angle between the intersection line of the fissure surface and the horizontal plane and the true north direction; “dip” means the angle between the inclined line of the fracture surface and the true north direction; “dip angle” means the the angle between the inclined line of the fracture surface and the horizontal plane. This is a commonly used method for defining occurrence in geology.

For the use of "orientation", we mainly use orientation to represent the angle between the fracture axis and the North direction, which is widely used in fracture geological surveys and site survey results are also expressed in this way. And 'azimuth' represents the overall orientation of the crack in space, including orientation, dip, and strike. Considering the need to represent three azimuth angles in the article, this representation method was used. We have thoroughly checked the use of these proprietary terms in the article according to this standard.

 

Comment 9. Some figures, like Figure 8 and Figure 15, are critical but could be improved. Ensure that the 7 microseismic planes in Figure 8 are clearly distinguishable, perhaps by using a more distinct color palette. In Figure 15, the schematic (h) should be larger and more clearly linked to the subplots (a-g). Adding a legend that explicitly maps colors to magnitude ranges in these plots would also be helpful.

Author response: Thank you for pointing this out. As suggested by the reviewer, these drawings have been modified in the revised manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript explores microseismicity in HDR reservoirs, highlighting fracture orientation's impact on seismic events and advocating proppant diversion over cyclic injection for better mitigation. However, the research methodology, interpretation, and presentation of results are subject to several concerns that diminish the validity and impact of the review findings. Critical points require addressing as follows: 

• Page 1 lines 14-30—The beginning of abstract lacks a clear statement of work’s relevance explaining the importance of the work and what exactly the MS will solve. Moreover, try to reduce it while highlighting the maim findings as quantitative results.
• This is not merely a citation gap—it reflects a fundamental unawareness of the current state of knowledge in croseismic generation mechanisms during hydraulic stimulation. There is a clear absence of novelty in the presented work and the authors need to review and show all the related works and their main limitations that the work overcome them. The authors are required to explain the novelties in a clear way. More details are required.
• I highly recommend the authors to add a flowchart by the end of the introduction showing the main steps by steps that have done in the work.
• he numerical methodology suffers from critical ambiguities that invalidate the reliability of the conclusions: Why was the original DFN of ~12 million fractures reduced to ~82,000? What quantitative criteria governed fracture “merging and removal” (lines 267–270)? How was the impact of this aggressive simplification on fracture connectivity, permeability anisotropy, and stress shadowing assessed? Why is there no mesh sensitivity analysis, despite the authors’ own admission that coarser discretization inflates event magnitudes (lines 188–197)? How can the authors claim “larger microseismic events” (line 22) when magnitude is directly tied to element area (Eq. 8), and no normalization or convergence study is presented?
• Why was the model not calibrated or validated against any of this available field data? Without demonstrating that the model can qualitatively or quantitatively reproduce observed pressure responses, fracture propagation, or microseismic event distributions from the actual site, all subsequent results and conclusions about mechanisms and mitigation remain unverified and purely speculative.
• How does calculating the seismic moment over an entire mesh element (Equation 8) represent the physical process of a shear rupture, which initiates on a small patch and propagates? Treating the entire element's area as the rupture area will inherently produce magnitudes that are artifacts of the mesh size rather than representations of true physical processes.
• How was this conclusion derived from the simulation results, given that no proppant transport or effect was modeled? The recommendation is purely speculative and is not backed by any data or analysis within the manuscript. Furthermore, the immense practical challenges of selectively placing proppant into specific, deep, critically-oriented fractures are completely ignored, making the proposal seem detached from field-operational realities.
• Pages 21-22 lines 578-615, the conclusion needs improvements, as an original work, it is recommended to provide main findings that explain your findings, not only add general findings or describe your work. Moreover, the authors must briefly provide the main limitations of their works and the future directions.
• Double check for the grammar.
• Add a table of nomenclature defining all the abbreviation in the MS after the 6th section.
• Most figures are blurry, lack resolution, or omit essential details. The authors should maintain the quality of all figures more than 300 DPI. Moreover, the authors are required to maintain the same size and style of text in all figures.

Comments on the Quality of English Language

Proofreading is required. 

Author Response

Responses to Reviewer #2

The manuscript explores microseismicity in HDR reservoirs, highlighting fracture orientation's impact on seismic events and advocating proppant diversion over cyclic injection for better mitigation. However, the research methodology, interpretation, and presentation of results are subject to several concerns that diminish the validity and impact of the review findings. Critical points require addressing as follows:

Author response: Thanks for your constructive suggestions and positive comments. We have now revised the manuscript following your comments carefully. Below are point-by-point responses to your comments, indicating the page/line for each of the changes. The corresponding modifications and corrections were made and highlighted in the revised manuscript.

 

Comment 1. Page 1 lines 14-30—The beginning of abstract lacks a clear statement of work’s relevance explaining the importance of the work and what exactly the MS will solve. Moreover, try to reduce it while highlighting the maim findings as quantitative results. This is not merely a citation gap—it reflects a fundamental unawareness of the current state of knowledge in croseismic generation mechanisms during hydraulic stimulation. There is a clear absence of novelty in the presented work and the authors need to review and show all the related works and their main limitations that the work overcome them. The authors are required to explain the novelties in a clear way. More details are required.

Author response: We agree with the reviewer’s assessment. As suggested by the reviewer, we have revised the Abstract in the revised manuscript.

 

Comment 2. I highly recommend the authors to add a flowchart by the end of the introduction showing the main steps by steps that have done in the work.

Author response: Thanks for your advice. Based on your suggestions, we have made detailed revisions to the last part of the Introduction regarding the research content of this article, highlighting the logical flow of the work and the content (in Page 3 Lines 98-121).

 

Comment 3. The numerical methodology suffers from critical ambiguities that invalidate the reliability of the conclusions: Why was the original DFN of ~12 million fractures reduced to ~82,000? What quantitative criteria governed fracture “merging and removal” (lines 267–270)? How was the impact of this aggressive simplification on fracture connectivity, permeability anisotropy, and stress shadowing assessed? Why is there no mesh sensitivity analysis, despite the authors’ own admission that coarser discretization inflates event magnitudes (lines 188–197)? How can the authors claim “larger microseismic events” (line 22) when magnitude is directly tied to element area (Eq. 8), and no normalization or convergence study is presented?

Author response: We appreciate the comments; they were very helpful in improving the manuscript.

The original manuscript did not adequately describe the generation and simplification process of the fracture network; this has been supplemented in the revised version.

For the simplification of the fracture network, the reference method officially provided by Itasca 3DEC was mainly used. The 3DEC software includes built-in tools for fracture connectivity analysis, fracture orientation analysis, and fracture merging, which facilitate the simplification of the fracture network. Regarding whether the simplification would cause changes in the results, we have previously conducted studies on fracturing injection as well as rock deformation and permeability evolution (see Reference [48]: Investigation of the effect of different injection schemes on fracture network patterns in hot dry rocks - A numerical case study of the FORGE EGS site in Utah). The results indicate that the conclusions obtained from macroscopic and microscopic perspectives are largely consistent and can be reconciled with observations from field experiments; in other words, the impact of this simplification on the analysis of hydraulic fracturing is acceptable.

An explanation regarding whether mesh discretization affects microseismic event calculations has been added to the manuscript. The main point is that, given the requirements of mechanical and fluid computations, the mesh cannot be discretized excessively coarsely. Once the mesh density reaches a certain level, its influence on microseismic event calculations is substantially reduced, and the computed microseismic magnitudes and frequencies converge toward stable values. Moreover, a mesh density that satisfies the requirements for mechanical and fluid computations does not affect the spatial distribution of microseismic events.

 

Comment 4. Why was the model not calibrated or validated against any of this available field data? Without demonstrating that the model can qualitatively or quantitatively reproduce observed pressure responses, fracture propagation, or microseismic event distributions from the actual site, all subsequent results and conclusions about mechanisms and mitigation remain unverified and purely speculative.

Author response: Thank you for your comments. The site data used in this study come from Utah FORGE well 58-32, which was drilled as an enhanced geothermal reservoir exploration well and for conducting some site characterization tests (e.g., in-situ stress measurements, initial permeability, etc.). No large-scale injection stimulation was performed in this well; therefore, there are no measured data from well 58-32 available for comparison. However, another geothermal well located near well 58-32 (approximately 500 m away) underwent stimulation tests. According to published results (Reference [50]: Circulation experiments at Utah FORGE: Near-surface seismic monitoring reveals fracture growth after shut-in), when the total injected volume and injection rate were comparable, the site microseismic monitoring reported a maximum magnitude of Mw 0.25–0.3, which is consistent with the model-calculated result (Mw 0.27). Those information has been added in the manuscript.

 

Comment 5. How does calculating the seismic moment over an entire mesh element (Equation 8) represent the physical process of a shear rupture, which initiates on a small patch and propagates? Treating the entire element's area as the rupture area will inherently produce magnitudes that are artifacts of the mesh size rather than representations of true physical processes.

Author response: Thank you for the comment. We also considered this issue during the simulation; therefore, when generating the mesh we applied discretization not only to the blocks but also to the fracture surfaces. The mesh on the fracture surfaces is relatively fine (maximum element size in the central regions approximately 0.5–1.0 m), which both meets the accuracy requirements for fluid and solid mechanics calculations and ensures that the fracture rupture process can be transmitted across the fracture surface. The successive failure of elements along the same fracture therefore corresponds to the progressive development of fracture rupture along that fracture. For the computation of microseismic events, when the mesh size is small the results accumulate progressively with deformation within the elements, thereby yielding a more accurate representation of microseismic magnitudes. In contrast, if a coarser mesh is used, such elements require a higher initial stress to fail, and failure may initiate with the calculation producing microseismic magnitudes that are anomalously high, which is clearly inconsistent with reality. Based on preliminary tests, the microseismic results obtained using the current mesh are close to the field-measured data; therefore we selected this mesh density for the calculations.

 

Comment 6. How was this conclusion derived from the simulation results, given that no proppant transport or effect was modeled? The recommendation is purely speculative and is not backed by any data or analysis within the manuscript. Furthermore, the immense practical challenges of selectively placing proppant into specific, deep, critically-oriented fractures are completely ignored, making the proposal seem detached from field-operational realities.

Author response: Thank you for the comments. The wording in the manuscript may have caused a misunderstanding. In hydraulic stimulation of hot dry rock, water injection is typically used in most cases to induce fracture opening. Here we intended to refer to the injection of fracturing fluid rather than the injection of proppant in the traditional sense. Therefore, the simulations only analyze water injection and the mechanics and flow issues of fluid–solid coupled interaction.

To prevent fracturing fluid from entering specific fractures, staged fracturing or temporary plugging techniques within the well can be employed. Many researchers are currently studying these methods and some results have already been obtained. We have added the corresponding explanation and references in the manuscript (Lines 536–542).

 

Comment 7. Pages 21-22 lines 578-615, the conclusion needs improvements, as an original work, it is recommended to provide main findings that explain your findings, not only add general findings or describe your work. Moreover, the authors must briefly provide the main limitations of their works and the future directions.

Author response: Thanks for your opinion, the part of limitations has been added in the manuscript. And the Conclusion part also has been modified.

 

Comment 8. Double check for the grammar.

Author response: Thanks for your opinion, all of the grammar have been double checked.

 

Comment 9. Add a table of nomenclature defining all the abbreviation in the MS after the 6th section. Most figures are blurry, lack resolution, or omit essential details. The authors should maintain the quality of all figures more than 300 DPI. Moreover, the authors are required to maintain the same size and style of text in all figures.

Author response: Thanks for your opinion, The resolution and text in the figure has been modified. In addition, all abbreviations in the article were checked to ensure that they were used for the first time.

Reviewer 3 Report

Comments and Suggestions for Authors

COMMENTS

ABSTRACT

• The abstract is poorly constructed; it should follow the standard format for a research article.
• It does not explicitly state the problem or research objective.
• Methodological details are limited.
• The conclusion is short and lacks a final sentence summarizing the scientific contribution.

1. INTRODUCTION

• The knowledge gap is not clearly defined; it is unclear what remains unknown.
• There is no explicit and clear statement of the central objective (it is suggested to include this as the final paragraph of the introduction).

2. DATA AND METHODOLOGY

• In a research article, a section “Data” or “Data and Methods” is essential, detailing the study area, sources and original data (e.g., microseismic records, rock properties, stresses, pore pressure, fracture geometry), and step-by-step methodology (software, parameters, calibrations, validations), clearly separating input data from derived results.
• In the manuscript, this information is not clearly distinguished: no raw data tables/appendices, mostly processed parameters, missing site location and geological context, and methodology limited to general descriptions without explaining how parameters were obtained/applied.
• This compromises traceability, reproducibility, and credibility, and even leaves doubts whether this is a real case or a hypothetical exercise.
• A major revision is recommended, adding explicit sections for Study Area, Data, and Methods, including original datasets in supplementary material, and clearly distinguishing inputs vs. outputs.

3. Numerical Simulation Procedure
4. Lack of concrete data:
• Input parameters are not specified (mechanical properties of fractures, permeability, initial stresses).
• No raw data tables or appendices.
5. Incomplete methodology:
• Explains “how the model works” but not the specific steps taken in this study.
• Order of methods and calibration criteria are unclear.
6. Limited reproducibility:
• 3DEC and FISH are mentioned, but without documenting configurations (software version, mesh, boundary conditions, convergence).
• Without this information, other researchers cannot replicate the results.
7. Disconnection with the study area:
• Although FORGE is later introduced as the base site, this section does not integrate its data or explain how they were applied in the model.
• The procedure appears generic, more like a theoretical manual than an applied methodology.
• The section presents the mathematics, but for a research paper it lacks data, reproducible steps, and explicit application to the case study.
8. Numerical Model

• Section 3 gives a general overview of the numerical model construction, but omits essential elements for a scientific article: original data, full parameters, and validation.
• In its current form, it reads more like a conceptual example than a fully data-based model. This undermines credibility and reproducibility.

Figure 2

The manuscript’s description is too superficial. It only mentions 251 fractures from a survey but does not explain:

• Geological interval,
• Classification criteria,
• Analysis procedure,
• How these data were integrated into the DFN model.
  Thus, the figure is more illustrative than scientifically reproducible.

Sentence (Line 269–271):
“A large number of fractures were removed and merged during this simplification process, which resulted in the inconsistency of Fig. 3a and Fig. 2b.”
The reference to Fig. 2b may be incorrect; it likely should be Fig. 3b.

Figure 3

• More illustrative than scientific; lacks numerical data and clear simplification criteria.

Figure 4

• It must be clarified how these models were obtained, for transparency and reproducibility.

3.3 Reservoir Model

• This section lacks raw data, justification of modeling parameters, and clear connection with site geology. Useful as a technical description, but insufficient for a reproducible scientific article.

Table 2

• Should explicitly state which values are from direct measurements and which are inferred/modeled.

4. Results and Analyses

• In the classical IMRaD structure, after Methods the next section should be:
• Results = objective presentation of findings.
• Discussion = critical interpretation, comparison with literature, limitations, and implications.
• The term “Results and Analyses” is uncommon in high-impact scientific publishing.
• “Analysis” is usually considered part of Methods.
• Using this label risks making the article look more like a technical report than a research paper.
• The section should be titled “Results and Discussion” and rewritten accordingly.

RESULTS

1. Numerical parameters, boundary conditions, and validations are not described in detail to allow replication.
2. No comparison with field microseismic records (results remain purely numerical).
3. Limited scientific discussion: Some parts are descriptive with little critical comparison to recent literature.
4. The manuscript lacks a clearly defined research question and objective, leaving results disconnected from the title.

This weakens the contribution, since a research article must explicitly address a scientific problem.

Figure 6

• There is incoherence between the problem statement (applied to FORGE) and the data (purely simulated).
• This should have been clarified from the abstract and methods: the study is a conceptual numerical simulation inspired by FORGE, not based on real seismic data.

Major Negative Aspects

1. Mismatch between framing and results
• Study is presented as applied to FORGE but uses no real microseismic data.
• Creates a serious imbalance between what the abstract/title promises and what is delivered.
2. Methodological shortcomings
• No clear Data section (geological or seismic).
• Methodology lacks detail for reproducibility (fracture segmentation, simplification criteria, numerical parameters, software, validation).
3. Simulated results without validation
• All microseismic figures are numerical outputs, with no comparison to observed data.
• As such, results are conceptual exercises rather than applied research.
4. Weak discussion and conclusions
• Discussion repeats result instead of interpreting them critically with literature.
• Conclusions are more a summary than a scientific contribution.
5. In its current state, the study does not meet standards for publication as a research article in a serious journal.
6. In its present state, the paper resembles a conceptual modeling exercise rather than applied research. It might be reformulated as a technical note or methodological paper, but not as an applied case study.

Comments on the Quality of English Language

The English language need to be improved

Author Response

Responses to Reviewer #3

Comment 1. ABSTRACT

The abstract is poorly constructed; it should follow the standard format for a research article. It does not explicitly state the problem or research objective. Methodological details are limited. The conclusion is short and lacks a final sentence summarizing the scientific contribution.

Author response: We agree with the reviewer’s assessment. As suggested by the reviewer, we have revised the Abstract in the revised manuscript.

 

Comment 2. INTRODUCTION

The knowledge gap is not clearly defined; it is unclear what remains unknown. There is no explicit and clear statement of the central objective (it is suggested to include this as the final paragraph of the introduction).

Author response: Thanks for your opinion, the Introduction part have been modified. A summary part and a description of the research content has been added, and the knowledge gap has been emphasized in the revised manuscript (in Page 3 Lines 98-121).

 

Comment 3. DATA AND METHODOLOGY

In a research article, a section “Data” or “Data and Methods” is essential, detailing the study area, sources and original data (e.g., microseismic records, rock properties, stresses, pore pressure, fracture geometry), and step-by-step methodology (software, parameters, calibrations, validations), clearly separating input data from derived results.

In the manuscript, this information is not clearly distinguished: no raw data tables/appendices, mostly processed parameters, missing site location and geological context, and methodology limited to general descriptions without explaining how parameters were obtained/applied.

This compromises traceability, reproducibility, and credibility, and even leaves doubts whether this is a real case or a hypothetical exercise.

A major revision is recommended, adding explicit sections for Study Area, Data, and Methods, including original datasets in supplementary material, and clearly distinguishing inputs vs. outputs.

Author response: Thank you for pointing this out.

This study’s modeling was conducted based on previously published fracture surveys and site fracture models. The original field data from the site fracture surveys were not used in the modeling, nor were any other required raw data present. For DFN modeling, we generated the initial fracture network using a stochastic generation method. This approach requires only distribution functions of fracture orientation and size, and the forms and parameter values of these functions were determined based on published results (References [44,46,48]).

For other details of the modeling, additional experts proposed revision suggestions, which we have reviewed and incorporated into the manuscript.

 

Numerical Simulation Procedure

Comment 4. Lack of concrete data: Input parameters are not specified (mechanical properties of fractures, permeability, initial stresses). No raw data tables or appendices.

Author response: Thank you for the comments; these parameters have been checked and included in the revised manuscript.

The mechanical properties of the fractures and the initial state of the rock mass (initial stress, initial permeability, etc.) are described in Section 3.4 (lines 326–347). The methods for calculating fracture permeability and deformation are detailed in Section 2.1.

 

Comment 5. Incomplete methodology: Explains “how the model works” but not the specific steps taken in this study. Order of methods and calibration criteria are unclear.

Author response: Thanks for your comments. The problem you mentioned has already been corrected in the article.

 

Comment 6. Limited reproducibility: 3DEC and FISH are mentioned, but without documenting configurations (software version, mesh, boundary conditions, convergence). Without this information, other researchers cannot replicate the results.

Author response: Thanks for the suggestions; we have reviewed and supplemented the mentioned information and have included it in the manuscript.

The 3DEC software version is 5.2, which is indicated in the manuscript (lines 126-127); details regarding the mesh, boundary conditions, and related information are described in detail in Sections 3.3 and 3.4. FISH is a function of 3DEC.

Comment 7. Disconnection with the study area: Although FORGE is later introduced as the base site, this section does not integrate its data or explain how they were applied in the model. The procedure appears generic, more like a theoretical manual than an applied methodology. The section presents the mathematics, but for a research paper it lacks data, reproducible steps, and explicit application to the case study.

Author response: We agree with the reviewer’s assessment. In this study, the research we envisioned is a generalized investigation, and the conclusions obtained concern which fractures in fractured reservoirs are more likely to generate microseismicity and why these fractures produce microseismic events. These conclusions are general rather than being applicable only to the FORGE site. Based on this idea, the manuscript details how to construct models beginning with the results of site fracture surveys (rather than the raw data from those surveys), and how analysis of those models yields general findings—for example, that fractures of certain specific orientations are more prone to producing microseismicity. This result is not limited to the FORGE site; it can also serve as a reference for other reservoir stimulation projects.

 

Comment 8. Numerical Model

Section 3 gives a general overview of the numerical model construction, but omits essential elements for a scientific article: original data, full parameters, and validation. In its current form, it reads more like a conceptual example than a fully data-based model. This undermines credibility and reproducibility.

Author response: Thank you for pointing this out. Section 3 demonstrates the process of constructing a reservoir fracturing model based on the site’s actual fracture survey results; the details of this process are presented in this section. However, because well 58-32, which was used in the study, did not have microseismic monitoring, we had no data available to calibrate the model. Instead, we used microseismic monitoring results from another nearby geothermal well within the same field to provide indirect validation of the model’s effectiveness. The monitoring results indicate that the maximum magnitude of microseismic events induced by fracturing in this block is approximately Mw 2.5–3.0. The results computed by the model are consistent with this conclusion. Therefore, we consider the model’s validity and accuracy to be confirmed.

In addition, following suggestions, we have revised the description of the modeling process to make this section easier to understand and to facilitate reproduction of the model proposed in this study.

 

Comment 9. Figure 2 The manuscript’s description is too superficial. It only mentions 251 fractures from a survey but does not explain:

Geological interval,

Classification criteria,

Analysis procedure,

How these data were integrated into the DFN model.

Thus, the figure is more illustrative than scientifically reproducible.

Author response: Thank you for pointing this out. Because our modeling establishes the DFN model by generating random fractures, this generation method is based on the fracture distribution functions and the values of the function parameters. The fracture distribution functions and the parameter values in those functions are reported directly in a published paper (Reference [46]: Effect of natural fractures on determining closure pressure). When performing fracture modeling, we only use the distribution functions of the fracture sets and their parameters to generate random fractures to construct the DFN, rather than using the site’s original fracture survey data for modeling.

In the DFN construction, we first generate a random fracture network according to the fracture distribution functions, but this network is too complex to be used further, so we subsequently simplify the DFN using connectivity and the spatial relationships among fractures. The detailed construction and simplification steps have been added to the manuscript.

 

Comment 10. Sentence (Line 269–271): “A large number of fractures were removed and merged during this simplification process, which resulted in the inconsistency of Fig. 3a and Fig. 2b.” The reference to Fig. 2b may be incorrect; it likely should be Fig. 3b.

Author response: Thank you for pointing this out. As suggested by the reviewer, this part have been revised and modified in the revised manuscript.

 

Comment 11. Figure 3 More illustrative than scientific; lacks numerical data and clear simplification criteria.

Author response: Thank you for pointing this out. As suggested by the reviewer, it has been supplemented in the revised manuscript.

 

Comment 12. Figure 4 It must be clarified how these models were obtained, for transparency and reproducibility.

Author response: Thank you for pointing this out. As suggested by the reviewer, this has been clarified in the revised manuscript. The model in Figure 4 is obtained by cutting the complete block using the simplified DFN established in Figure 3. This cutting process can be automatically achieved through 3DEC, which is also a basic function of 3DEC software. These contents are described in detail in lines 301-324 of the manuscript. We believe that based on these statements, under the condition that users understand the operation methods of 3DEC, they can replicate the exact same model as mentioned in the article.

 

Comment 13. 3.3 Reservoir Model This section lacks raw data, justification of modeling parameters, and clear connection with site geology. Useful as a technical description, but insufficient for a reproducible scientific article.

Author response: Thank you for pointing this out. The problem you mentioned has already been corrected in the article. In this paper the modeling progress does not require the raw data from site fracture surveys; our modeling starts from the distribution functions of the fractures. Accordingly, we have cited the site-measured data and present in the paper the distribution functions of fracture attitudes and sizes derived from the site fracture survey. We have cited the articles on site investigation and fracture statistical analysis in the corresponding positions in the manuscript.

 

Comment 14. Table 2 Should explicitly state which values are from direct measurements and which are inferred/modeled.

Author response: Thanks for your advice. As suggested by the reviewer, the source of the data has been annotated in the revised amnuscript (in Page 9 Lines 326-338).

 

Comment 15. Results and Analyses

In the classical IMRaD structure, after Methods the next section should be:

Results = objective presentation of findings.

Discussion = critical interpretation, comparison with literature, limitations, and implications.

The term “Results and Analyses” is uncommon in high-impact scientific publishing.

“Analysis” is usually considered part of Methods.

Using this label risks making the article look more like a technical report than a research paper.

The section should be titled “Results and Discussion” and rewritten accordingly.

Author response: Thank you for pointing this out. As suggested by the reviewer, the manuscript has been revised and modified.

 

Comment 16. RESULTS

Numerical parameters, boundary conditions, and validations are not described in detail to allow replication.

No comparison with field microseismic records (results remain purely numerical).

Limited scientific discussion: Some parts are descriptive with little critical comparison to recent literature.

The manuscript lacks a clearly defined research question and objective, leaving results disconnected from the title.

This weakens the contribution, since a research article must explicitly address a scientific problem.

Author response: Thank you for pointing this out. We have revised the manuscript in accordance with the comments raised.

 

Comment 17. Figure 6 There is incoherence between the problem statement (applied to FORGE) and the data (purely simulated). This should have been clarified from the abstract and methods: the study is a conceptual numerical simulation inspired by FORGE, not based on real seismic data.

Author response: Thanks for the valuable advice. We agree with the reviewer’s assessment, some statements in the article may cause misunderstandings. As suggested by the reviewer, the manuscript has been revised and the abstract has been rewritten.

 

Comment 18. Mismatch between framing and results. Study is presented as applied to FORGE but uses no real microseismic data. Creates a serious imbalance between what the abstract/title promises and what is delivered.

Author response: Thanks for the valuable advice. As suggested by the reviewer, the manuscript has been revised and the abstract has been rewritten.

 

Comment 19. Methodological shortcomings. No clear Data section (geological or seismic). Methodology lacks detail for reproducibility (fracture segmentation, simplification criteria, numerical parameters, software, validation).

Author response: Thank you for pointing this out. As suggested by the reviewer, the related content you mentioned has been added to the revised manuscript.

 

Comment 20. Simulated results without validation. All microseismic figures are numerical outputs, with no comparison to observed data. As such, results are conceptual exercises rather than applied research. Weak discussion and conclusions. Discussion repeats result instead of interpreting them critically with literature. Conclusions are more a summary than a scientific contribution. In its current state, the study does not meet standards for publication as a research article in a serious journal. In its present state, the paper resembles a conceptual modeling exercise rather than applied research. It might be reformulated as a technical note or methodological paper, but not as an applied case study.

Author response: Thank you for your constructive suggestions and positive comments. The site data used in this study come from Utah FORGE well 58-32, which was drilled as an enhanced geothermal reservoir exploration well and for conducting some site characterization tests (e.g., in-situ stress measurements, initial permeability, etc.). No large-scale injection stimulation was performed in this well; therefore, there are no measured data from well 58-32 available for comparison. However, another geothermal well located near well 58-32 (approximately 500 m away) underwent stimulation tests. According to published results (Reference [50]: Circulation experiments at Utah FORGE: Near-surface seismic monitoring reveals fracture growth after shut-in), when the total injected volume and injection rate were comparable, the site microseismic monitoring reported a maximum magnitude of Mw 0.25–0.3, which is consistent with the model-calculated result (Mw 0.27). As suggested by the reviewer, these information has been added in the revised manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Recommendation: Major Revision

The revised manuscript presents important modeling insights into the microseismic mechanisms during hydraulic stimulation of Hot Dry Rock reservoirs. However, a fundamental scientific error remains uncorrected regarding the use of earthquake magnitude, which directly affects the reliability of the analysis and interpretation. Furthermore, the authors have explained the magnitude scale incorrectly in the magnitude section. The revisions made are only partially appropriate and require correction.  
Correction and improvement in science  are continuous processes that never end; author  must recognize this and embrace necessary revisions.

Recent investigations published in several journals, including Applied Sciences, have clearly demonstrated that the Mw scale is not applicable to small-to-moderate earthquakes (below M 7.5). This limitation has been both theoretically established and empirically validated using global datasets (see Figures 1–3 in BSSA, 2019, and Das and Das 2025: “Limitations of Mw and M Scales: Compelling Evidence Advocating for the Das Magnitude Scale (Mwg)—A Critical Review and Analysis”).

In summary, the Mw scale was originally developed and validated only for Southern California, and its global applicability to smaller and medium events is scientifically unsupported (see recent literature ). Furthermore, there exists a mathematical flaw in its foundational derivation—Equation (1) of Prucaru and Bruchmaker (1978) is valid only for magnitudes below 7.0, yet it was incorrectly reproduced in a subsequent comment paper (see Das et al., 2025, for detailed clarification). Additionally, the use of the surface-wave magnitude (Ms) as a reference in the development of Mw was long ago objected to by Gutenberg and Richter (1958), as Ms reflects only surface effects and does not represent the full rupture process at depth.

The authors have also cited a comment paper based on scientifically incorrect facts, as demonstrated in recent literature (“A Finite-Element Simulation–Based Approach for Generating Site-Specific Ground Motion Database for the Charleston Seismic Source,” International Journal of Geomechanics, 2025; see also the detailed reply in Das and Das, 2025). This paper contains errors in the reproduction and interpretation of fundamental equations, leading to misleading conclusions. Such sources should not be used to justify methodological decisions in the present work.

The authors must revise the magnitude analysis section and provide a scientifically sound discussion of the limitations of the Mw scale. They may adopt the Mwg scale (Das Magnitude Scale) for improved accuracy, or, if they choose to retain Mw, must include a clear justification for using a scale known to be inappropriate for events below M 7.5, and explicitly explain how this limitation affects their interpretations.

Furthermore, the calculation of magnitude in the manuscript appears to be incorrect, as demonstrated by the comparison between Mw and Mwg values below:

Mw    Log Mo    Mwg    Absolute difference
0.2    16.35    -0.657941176    0.857941176
0.3    16.5    -0.547647059    0.847647059
0.4    16.65    -0.437352941    0.837352941
0.5    16.8    -0.327058824    0.827058824
0.6    16.95    -0.216764706    0.816764706
0.7    17.1    -0.106470588    0.806470588
0.8    17.25    0.003823529    0.796176471
0.9    17.4    0.114117647    0.785882353
1    17.55    0.224411765    0.775588235

LogMo = (Mw +10.7)*3/2
Mwg = LogMo/1.36-12.68

The authors must explicitly explain the well-known limitations of the Mw scale in the magnitude section (Microseismic Model). This correction is not time-consuming, as demonstrated above, and I am confident that the results will be significantly improved once the correction is implemented.

Until this fundamental issue is adequately resolved, the manuscript cannot be accepted in its present form.

 

Author Response

The revised manuscript presents important modeling insights into the microseismic mechanisms during hydraulic stimulation of Hot Dry Rock reservoirs. However, a fundamental scientific error remains uncorrected regarding the use of earthquake magnitude, which directly affects the reliability of the analysis and interpretation. Furthermore, the authors have explained the magnitude scale incorrectly in the magnitude section. The revisions made are only partially appropriate and require correction.

Recent investigations published in several journals, including Applied Sciences, have clearly demonstrated that the Mw scale is not applicable to small-to-moderate earthquakes (below M 7.5). This limitation has been both theoretically established and empirically validated using global datasets (see Figures 1–3 in BSSA, 2019, and Das and Das 2025: “Limitations of Mw and M Scales: Compelling Evidence Advocating for the Das Magnitude Scale (Mwg)—A Critical Review and Analysis”).

In summary, the Mw scale was originally developed and validated only for Southern California, and its global applicability to smaller and medium events is scientifically unsupported (see recent literature). Furthermore, there exists a mathematical flaw in its foundational derivation—Equation (1) of Prucaru and Bruchmaker (1978) is valid only for magnitudes below 7.0, yet it was incorrectly reproduced in a subsequent comment paper (see Das et al., 2025, for detailed clarification). Additionally, the use of the surface-wave magnitude (Ms) as a reference in the development of Mw was long ago objected to by Gutenberg and Richter (1958), as Ms reflects only surface effects and does not represent the full rupture process at depth.

The authors have also cited a comment paper based on scientifically incorrect facts, as demonstrated in recent literature (“A Finite-Element Simulation–Based Approach for Generating Site-Specific Ground Motion Database for the Charleston Seismic Source,” International Journal of Geomechanics, 2025; see also the detailed reply in Das and Das, 2025). This paper contains errors in the reproduction and interpretation of fundamental equations, leading to misleading conclusions. Such sources should not be used to justify methodological decisions in the present work.

The authors must revise the magnitude analysis section and provide a scientifically sound discussion of the limitations of the Mw scale. They may adopt the Mwg scale (Das Magnitude Scale) for improved accuracy, or, if they choose to retain Mw, must include a clear justification for using a scale known to be inappropriate for events below M7.5, and explicitly explain how this limitation affects their interpretations.

The authors must explicitly explain the well-known limitations of the Mw scale in the magnitude section (Microseismic Model). This correction is not time-consuming, as demonstrated above, and I am confident that the results will be significantly improved once the correction is implemented.

Until this fundamental issue is adequately resolved, the manuscript cannot be accepted in its present form.

 

 

Response:

Thank you for your comments again.

We carefully reviewed the magnitude calculation method you provided and consulted additional references. After careful consideration, we agree with your suggestion and have adopted the magnitude calculation method Mwg proposed by Das et al.

We have revised all magnitude analyses in the manuscript to use the Mwg method and have reanalyzed the data. The results show that this modification produces some effect on the numerical values of magnitudes, but has little impact on the trend analysis. Nevertheless, employing a more accurate magnitude calculation method is undoubtedly beneficial to the analyses.

All figures in the paper that involve magnitudes have been redrawn and the corresponding descriptions have been revised.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have implemented my comments; however, they have to add a table of nomenclature defining all the abbreviation in the MS after the 6th section.

Best regards.

Author Response

Thank you for your advice. The Nomenclatures Table has been updated after the "5.Conclusion" section.
The Nomenclatures Table includes all abbreviations and their full names that appear in the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

COMMENTS

1. Abstract
   The abstract introduces the HDR concept and quickly moves to hydromechanical simulation and microseismicity without clearly establishing the link between HDR importance and the seismic risk motivating the research. This results in a confusing read and weakens the paper’s objective.
   Rewrite the abstract (review what elements an abstract should contain).
2. Introduction
   a. Include references on coupled models to justify the numerical approach used.
   b. Clearly state what novelty or new knowledge the study provides.
   c. Explicitly define the objective of the study (at the end of the introduction), since as written it reads more like a narrative; the objective is confused with the model description and the central purpose of the study is not specified. Consequently, the study’s development is poorly framed.
   d. A location map of the study area is missing.
3. Missing Section: Data and Methodology
   a. The manuscript does not adequately describe the data used.
   Although it mentions information from well 58-32 at the FORGE site, it lacks transparency regarding the origin, type, and processing of the data used to build and validate the model. This limits reproducibility and reduces scientific rigor.
   b. Lines (213–241) describe well 58-32 at the FORGE site (Utah, USA); however, data sources (neither dataset nor FORGE repository) and acquisition or processing methods are not specified.
   c. The methodological section describes the numerical model but does not provide enough details about the data used. It would be advisable to clearly specify the origin, type, and resolution of the geological, thermal, and fracture data employed, and to include a summary table or link to the data source. The lack of this information limits reproducibility and numerical result validation.
   d. Although the DFN model is based on well 58-32 statistics, the massive generation of fractures through Fisher distribution implies predominant use of synthetic data. This is acceptable for a numerical study but should be explicitly stated and supported by validation against real microseismic records or field data from the FORGE site. Otherwise, the results should be interpreted as conceptual approximations rather than reliable quantitative projections.
   e. The results (Section 4) are purely comparative between injection scenarios, without contrast against empirical evidence.
   f. The presented results (spatial distribution, magnitude, and cyclic injection effects) are internally consistent but cannot be considered verified without comparison to field measurements.
   This limits the work to a conceptual or exploratory study, not predictive or validated.
4. Results and Analyses Section
   a. These should be presented in separate sections:
• Results
• Analysis
5. Discussion
   The manuscript lacks a Discussion section contrasting the results with previous studies or validating interpretations against real observations. It is recommended to include a “Discussion” section analyzing agreements and discrepancies with recent experimental and numerical studies, as well as the practical implications of the results. This would strengthen the scientific soundness and originality of the study.
   This section should also include the study’s limitations, especially the lack of validation with real data (toward the end of the Discussion).
6. Conclusions
   The conclusions provide a descriptive summary of the results but do not properly explain how these address the study’s objectives nor offer a critical interpretation. It is recommended to reformulate them by emphasizing the most relevant findings and model limitations. Including future research prospects would strengthen the scientific closure of the manuscript.

Other Observations

• The manuscript’s figures do not clearly describe their analytical purpose nor are they interpretively integrated with the text. It is recommended to rewrite the figure captions to explain what each demonstrates (e.g., relationship between orientation and magnitude of microseisms, or temporal evolution of the event). They must also include units, scales, and spatial or temporal references.
• The manuscript is not properly structured nor methodologically solid for a standard scientific publication.
• The manuscript should be written following the IMRaD format (Introduction, Materials, Methods, Results, Discussion, and Conclusions) required by most indexed journals.

Comments on the Quality of English Language

Engllish language need to be improved

Author Response

COMMENTS

 

Abstract

The abstract introduces the HDR concept and quickly moves to hydromechanical simulation and microseismicity without clearly establishing the link between HDR importance and the seismic risk motivating the research. This results in a confusing read and weakens the paper’s objective.

Rewrite the abstract (review what elements an abstract should contain).

Response: We have revised the abstract based on your comments.

Introduction

1. Include references on coupled models to justify the numerical approach used.

Response: Thank you for your suggestion; it was very helpful to us. We have added this content to the model construction and analysis methods section, see reference [44] (line 246).

1. Clearly state what novelty or new knowledge the study provides.

Response: Thank you for your suggestion. We have added a paragraph at the end of the introduction to address the previously missing discussion of the manuscript's novelty and the new knowledge it provides.

1. Explicitly define the objective of the study (at the end of the introduction), since as written it reads more like a narrative; the objective is confused with the model description and the central purpose of the study is not specified. Consequently, the study’s development is poorly framed.

Response: Thank you for your suggestion; we have added this part to the final paragraph of the Introduction.

1. A location map of the study area is missing.

Response: A dedicated section (2.2) in the paper introduces the site; this section includes a location map of the study area and the site (Figure 1).

 

 

Missing Section: Data and Methodology

1. The manuscript does not adequately describe the data used.

Although it mentions information from well 58-32 at the FORGE site, it lacks transparency regarding the origin, type, and processing of the data used to build and validate the model. This limits reproducibility and reduces scientific rigor.

1. Lines (213–241) describe well 58-32 at the FORGE site (Utah, USA); however, data sources (neither dataset nor FORGE repository) and acquisition or processing methods are not specified.
2. The methodological section describes the numerical model but does not provide enough details about the data used. It would be advisable to clearly specify the origin, type, and resolution of the geological, thermal, and fracture data employed, and to include a summary table or link to the data source. The lack of this information limits reproducibility and numerical result validation.

Response for a~c: This study did not use any specific site datasets; we only constructed DFNs using published fracture distribution results. We have previously conducted and completed validation and analysis based on this fracture network, and the results indicate that the fracture-network-based model meets the accuracy requirements for analysis of fractured reservoirs subjected to hydraulic fracturing (see References [44] and [48]).

Using the functions provided within the 3DEC software, the full set of models used in this study can be reproduced exactly from the parameters mentioned in the paper, and this is the approach we followed. This method of generating fracture networks and fractured reservoirs has many other precedents in the literature (see References [47], [49]); therefore, there is no model construction process or sequence that necessarily requires the use of particular datasets.

1. Although the DFN model is based on well 58-32 statistics, the massive generation of fractures through Fisher distribution implies predominant use of synthetic data. This is acceptable for a numerical study but should be explicitly stated and supported by validation against real microseismic records or field data from the FORGE site. Otherwise, the results should be interpreted as conceptual approximations rather than reliable quantitative projections.
2. The results (Section 4) are purely comparative between injection scenarios, without contrast against empirical evidence.
3. The presented results (spatial distribution, magnitude, and cyclic injection effects) are internally consistent but cannot be considered verified without comparison to field measurements.

This limits the work to a conceptual or exploratory study, not predictive or validated.

Response for d~f: Thank you for the comments; they have been very helpful to us.

However, as you noted, this study is a conceptual qualitative analysis conducted based on the actual conditions at the site and does not contain any quantitative predictive conclusions. The study primarily used the publicly available fracture statistical distribution results from the FORGE site to construct a DFN and fracture medium for investigation, and employed this model to analyze the intrinsic connections between injection-induced microseismicity and the distribution and fracture behavior of fractures. Because the site’s microseismic data are not public and the injection procedure we simulated is novel and has not been carried out in the field, we did not have available field monitoring data to calibrate and validate the model. Nevertheless, these injection procedures have been studied and shown to influence post-injection fracture behavior (see References [44], [48]), which is why we conducted this research in the absence of field data.

Given that this study is merely conceptual and exploratory, and we do not present any strictly precise quantitative predictive conclusions, we believe the findings retain some referential value even without validation by actual field data. This also underscores the need for microseismic monitoring at the site in subsequent studies and further justifies the necessity of continuing this line of research.

 

Results and Analyses Section

1. These should be presented in separate sections:

Results

Analysis

Discussion

The manuscript lacks a Discussion section contrasting the results with previous studies or validating interpretations against real observations. It is recommended to include a “Discussion” section analyzing agreements and discrepancies with recent experimental and numerical studies, as well as the practical implications of the results. This would strengthen the scientific soundness and originality of the study.

This section should also include the study’s limitations, especially the lack of validation with real data (toward the end of the Discussion).

Response：We appreciate the comments raised and have added a discussion section. Regarding the absence of validation due to the lack of microseismic data, we have provided a specific explanation at the end of the manuscript.

Conclusions

The conclusions provide a descriptive summary of the results but do not properly explain how these address the study’s objectives nor offer a critical interpretation. It is recommended to reformulate them by emphasizing the most relevant findings and model limitations. Including future research prospects would strengthen the scientific closure of the manuscript.

Response: Thank you for the comments. We have added a discussion of the study's limitations and how the proposed recommendations might be implemented at the end of the manuscript (lines 682–695). In that section we specifically emphasize the impact of the lack of onsite microseismic data on the study and note that the conclusions of this research are qualitative.

Other Observations

The manuscript’s figures do not clearly describe their analytical purpose nor are they interpretively integrated with the text. It is recommended to rewrite the figure captions to explain what each demonstrates (e.g., relationship between orientation and magnitude of microseisms, or temporal evolution of the event). They must also include units, scales, and spatial or temporal references.

The manuscript is not properly structured nor methodologically solid for a standard scientific publication.

The manuscript should be written following the IMRaD format (Introduction, Materials, Methods, Results, Discussion, and Conclusions) required by most indexed journals.

Response: We have revised the manuscript’s structure and the figure captions according to the comments you raised; the changes have been marked in red.

 

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Minor Review Comment:

The manuscript is generally well-written and clearly presented. All sections are coherent and technically sound. However, to strengthen the justification of the chosen magnitude scale and improve the clarity of the methodology, it is suggested to include the following explanatory paragraph immediately after Eq. (9):

“According to Das et al. (2019), microseismic magnitudes can be calculated based on the seismic moment (Eq. (9)). Compared with the commonly used moment magnitude (Mw), magnitudes obtained by this method provide more accurate results for the analysis of very small-magnitude earthquakes.
  SEE EQUATION IN WORD FILE ......   (9)

This study adopts the Mwg scale because it provides a more reliable estimation of microseismic magnitudes, particularly for small- and medium-magnitude events. Traditional magnitude scales such as Mw have known limitations. In particular, the Mw scale has a mathematical inconsistency when applied below Ms 7.5, as it was derived using Eq. (1) from Purcaru and Berckhemer (1978), which is only valid for the range 5.0 ≤ Ms ≤ 7.0. This limitation is clearly reflected in observed data (see Figures 1–3 of Das et al., 2019). The Mw scale was developed and validated mainly for Southern California for magnitudes above 3.0. The Mw scale has been globally validated for magnitudes above 7.5 and performs reliably primarily for large, shallow earthquakes worldwide. It tends to yield inaccurate estimates for intermediate- and deep-focus events and often overestimates the energy release for smaller earthquakes. Furthermore, it assumes a constant energy-to-moment ratio (E/Mo = 5×10⁻⁵), which oversimplifies the complex energy radiation process and neglects regional variations. In contrast, the Mwg scale, derived from globally distributed data, provides statistically improved and energy-consistent results, making it more suitable for analyzing microseismic activity in this study.”

 

This addition would complete the explanation and provide a clear scientific rationale for using the Mwg scale.

 

Reference:  Purcaru G, Berckhemer H (1978) A magnitude scale for very large

Earthquakes. Tectonophysics 49:189–198

Comments for author File: Comments.pdf

Author Response

Comments:

The manuscript is generally well-written and clearly presented. All sections are coherent and technically sound. However, to strengthen the justification of the chosen magnitude scale and improve the clarity of the methodology, it is suggested to include the following explanatory paragraph immediately after Eq. (9):

“According to Das et al. (2019), microseismic magnitudes can be calculated based on the seismic moment (Eq. (9)). Compared with the commonly used moment magnitude (Mw), magnitudes obtained by this method provide more accurate results for the analysis of very small-magnitude earthquakes.

  SEE EQUATION IN WORD FILE ......   (9)

This study adopts the Mwg scale because it provides a more reliable estimation of microseismic magnitudes, particularly for small- and medium-magnitude events. Traditional magnitude scales such as Mw have known limitations. In particular, the Mw scale has a mathematical inconsistency when applied below Ms 7.5, as it was derived using Eq. (1) from Purcaru and Berckhemer (1978), which is only valid for the range 5.0 ≤ Ms ≤ 7.0. This limitation is clearly reflected in observed data (see Figures 1–3 of Das et al., 2019). The Mw scale was developed and validated mainly for Southern California for magnitudes above 3.0. The Mw scale has been globally validated for magnitudes above 7.5 and performs reliably primarily for large, shallow earthquakes worldwide. It tends to yield inaccurate estimates for intermediate- and deep-focus events and often overestimates the energy release for smaller earthquakes. Furthermore, it assumes a constant energy-to-moment ratio (E/Mo = 5×10⁻⁵), which oversimplifies the complex energy radiation process and neglects regional variations. In contrast, the Mwg scale, derived from globally distributed data, provides statistically improved and energy-consistent results, making it more suitable for analyzing microseismic activity in this study.”

This addition would complete the explanation and provide a clear scientific rationale for using the Mwg scale.

Reference:  Purcaru G, Berckhemer H (1978) A magnitude scale for very large

Earthquakes. Tectonophysics 49:189–198

Response: We think this is an excellent suggestion. As suggested by the reviewer, the explanation you mentioned has been added in the revised manuscript in Lines 211-223.

Reviewer 3 Report

Comments and Suggestions for Authors

After a second review of the manuscript, it is evident that the fundamental observations from the first round have not been adequately addressed.
Despite minor improvements in writing, figures, and references, the manuscript still does not follow the suggested IMRaD format, which is a basic requirement for scientific research articles.
The sections titled “Problem Setup” and “Results and Analysis” combine methodological and analytical content without clear separation, which compromises scientific rigor, reproducibility, and coherence.

In addition, weaknesses persist regarding:
• The overall organization of the text, which remains narrative rather than scientific.
• The insufficient separation between results and interpretation, affecting clarity and objectivity.
• The lack of a comprehensive response to previously communicated observations concerning structure, methodology, and validation.

Since this is the second review round and the authors have not implemented the essential corrections requested, I consider that a third review would be unproductive.
The manuscript does not meet the minimum standards of structure, methodology, and format required for publication.

Comments on the Quality of English Language

The English Language need to be improved

Author Response

Comment 1: After a second review of the manuscript, it is evident that the fundamental observations from the first round have not been adequately addressed. Despite minor improvements in writing, figures, and references, the manuscript still does not follow the suggested IMRaD format, which is a basic requirement for scientific research articles. The sections titled “Problem Setup” and “Results and Analysis” combine methodological and analytical content without clear separation, which compromises scientific rigor, reproducibility, and coherence.

Response: We sincerely thank the reviewer for this critical feedback of our work. We apologize for the previous oversight in fully addressing the structural concerns. We agree that adherence to the IMRaD format is essential for clarity, rigor, and reproducibility. As suggested by the reviewer, we have now comprehensively restructured the entire manuscript to strictly conform to the standard IMRaD format. The specific changes made are as follows:

Introduction: We have expanded the introduction to more clearly establish the research context, state the objectives, and outline the structure of the paper.

Methods: The content previously under the "Problem Setup" section has been thoroughly revised and integrated into a new, dedicated "Numerical Methods" section. This section now provides a complete and unambiguous description of the governing equations, numerical model setup, model parameters and simulation scheme to ensure full reproducibility.

Results: We have created a new, standalone "Simulation Results" section. This section now presents the findings of our study objectively, without interpretive discussion. All figures and tables have been repositioned and referenced within this section to support the presented data.

Discussion: The analytical and interpretive content from the previous "Results and Analysis" section has been moved into a distinct "Discussion" section. Here, we explicitly interpret the results, explain their significance, and relate them back to the research objectives and existing literature.

We believe this significant restructuring has decisively resolved the core issue raised. The manuscript now features a clear logical flow, a strict separation between methodology, findings, and interpretation, and fully meets the expected standards of a scientific research article. We are confident that these changes have greatly enhanced the manuscript's scientific rigor, reproducibility, and overall coherence.

Comment 2: In addition, weaknesses persist regarding: The overall organization of the text, which remains narrative rather than scientific. The insufficient separation between results and interpretation, affecting clarity and objectivity. The lack of a comprehensive response to previously communicated observations concerning structure, methodology, and validation.

Since this is the second review round and the authors have not implemented the essential corrections requested, I consider that a third review would be unproductive. The manuscript does not meet the minimum standards of structure, methodology, and format required for publication.

Response: We deeply apologize for our previous failure to adequately address the fundamental concerns regarding the manuscript's structure and scientific rigor. We fully acknowledge the seriousness of these shortcomings and the frustration they have caused. As suggested by the reviewer, we have eliminated the previous hybrid sections entirely. The manuscript now strictly adheres to the IMRaD format with clearly demarcated sections: Introduction, Methods, Results, and Discussion. The "Methods" section has been expanded and rewritten with meticulous detail to ensure full reproducibility. We have included all necessary protocols, parameters, and analytical procedures.

We respectfully request that the reviewer reconsiders our manuscript. We assure you that the current version is fundamentally different from the one previously reviewed. We have attached a version with highlighted changes to make the extent of our revisions immediately apparent. We are confident that these comprehensive corrections have now brought the manuscript in line with the minimum standards for structure, methodology, and format, and we are deeply committed to achieving the level of scientific rigor required for publication.

Thank you once again for your valuable guidance.