Early Post-Seismic Deformation Revealed After the Wushi (China) Earthquake (Mw = 7.1) Occurred on 22 January 2024

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper reports the study of the post seismic deformations observed after the Wushi earthquake (Mw =7.0) occurred in China on January 22, 2024. This earthquake is the second largest earthquake occurred in the seismic zone after the Suusamyr event (Ms=7.3) occurred in 1992. After the mainshock, the largest aftershock (Mw=5.7) occurred at January 29.

The main obtained results are: 1) a 11months post-seismic deformation was revealed and it was induced by a slip along the continuation of co-seismic fault, 2) a co-seismic displacement was observed at January 29 on the occasion of the largest aftershock; according the Authors this displacement could be produced by more than the Mw=5.7 event because its simulated seismic moment is Mw=5.88 that is larger than the experimental Mw=5.7; the Authors propose that this earthquake destabilized  another fault so that a relatively small event occurred as its aftershock.

The analysis of the co-seismic deformation reported in point 1) is satisfactory and well done. As it concerns the point 2), that is to propose the occurrence of a second event produced by the Mw=5.7 aftershock in order to justify an obtained simulated value (5.88) larger than the experimental one (5.7), I think that this difference could be explained more realistically taking into account the error theory (in experimental value). According to my opinion the model proposed by the Authors is too imaginative! In any case the Authors can propose it as a possibility but the measurement error previously I mentioned might be reported as a further possibility.

Some minor remark: 1) at pag.1 the focal depth is reported as 16.1Km; is better to indicate 16 Km because the previous precision is absurd! 2) I suggest to avoid to write M6, M5.7 and other; it is better to use the equal sign and to write M=6, M=5.7 and so on; 3) I suggest to change the title as “Seismic Deformations revealed after the Wushi (China) earthquake (Mw=7.0) occurred on January 22, 2024” or so on. 

Comments on the Quality of English Language

I am not a native English speaker but according to my opinion the language of the paper might be revised.

Author Response

Dear Reviewer,

Thank you very much for your kind consideration and valuable suggestions! We responsed to your suggestions point-by-point.

Please see the attachment.

Best regards!

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors calculated the early post-seismic deformation of the 2024 Mw 7.1 Wushi Earthquake using the Sentine-1 ascending and descending InSAS time series data. The results indicate that the post-seismic deformation was dominated by afterslip along the up-dip continuation of the coseismic fault. Overall, this article is well written. The method and model are reliable. I have two suggestions on the figures. The Figure1 should add the color bar for the topography, the length scale, and the North arrow.  The Figure 6 should add the information on the x-coordinate.

Author Response

Dear Reviewer,

Thank you very much for your kind consideration and valuable suggestions! We responsed to your suggestions point-by-point.

Please see the attachment.

Best regards!

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Using Sentinel-1 InSAR data, the authors investigated the 11-month post-seismic deformation following the Mw7.1 Wushe earthquake in 2024 and explored the Coulomb stress triggering relationships among the mainshock, aftershocks, and postseismic slip. The findings provide novel insights into the characteristics of blind thrust faults within the Tianshan seismic belt and possess significant scientific value. However, certain limitations exist in data processing, model assumptions, result interpretation, and discussion depth, which require further refinement to enhance the scientific rigor and readability of the paper:  

1. The seismic and tectonic background of the study area is inadequately explained. It is recommended that the authors provide additional clarification regarding the seismic activity and tectonic evolution history of the region. While the paper mentions that the Wushe earthquake was the largest in the southern Tianshan region in nearly a century, it lacks a detailed description of the seismic activity background. Furthermore, although the Tianshan tectonic belt and the tectonic location of the Wushe earthquake are briefly introduced, an in-depth analysis of the region's tectonic evolution history is missing, which limits the ability to fully explain the complex tectonic environment and earthquake occurrence mechanism.  
2. The authors note that no earthquakes of magnitude 6 or greater have occurred within 50 km of the Wushe earthquake since the 20th century. However, seismic activity exhibits spatial migration patterns. Given that the Wushe earthquake broke the approximately century-long quiet period of strong earthquakes in the southern Tianshan region, it is worth exploring whether this seismicity migrated from other areas. For instance, the Jiashi Mw6.0 earthquake in 2020 occurred within the same complex fold and fault zone region of the southern Tianshan Mountains, with temporal and spatial distances falling within the possible range of stress triggering. Is there a potential correlation between these two events?  
3. Studies indicate that the M7.1 Wushe earthquake did not produce significant surface rupture, whereas the largest Mw5.7 aftershock on January 29 generated a surface rupture equivalent to approximately M6.4. This phenomenon requires further explanation.  
4. InSAR data were processed using ISCE and MintPy, with tropospheric delay corrected using the ERA5 global atmospheric model. However, the specific effects of tropospheric correction are not described in detail. It is recommended to supplement comparative analyses (e.g., statistics or spatial distribution maps of phase residuals) before and after tropospheric delay correction to demonstrate its effectiveness. Additionally, the potential interference of environmental factors unique to the Tianshan region, such as changes in ground scattering caused by seasonal snow cover or drought, should be addressed, along with strategies for mitigating these effects.  
5. Path136 data did not cover the January 29 aftershock, necessitating the use of Path34 data for analysis. This time span includes deformation one week after the mainshock, potentially conflating coseismic signals from the aftershock with early post-earthquake deformation. Does direct inversion using such InSAR data affect the results? If further signal separation is not feasible, this limitation should be acknowledged in the text.  
6. The study primarily considers co-slip mechanisms and employs a uniform slip model for inversion. Post-earthquake deformation may be influenced by various factors, including viscoelastic relaxation and pore-elastic rebound. Focusing solely on a single mechanism may not fully account for the observed deformation characteristics. If insufficient data precludes further modeling, it is recommended to clarify the limitations of this assumption in the discussion and validate it with alternative datasets in future studies.  
7. It is assumed that the 11-month post-earthquake deformation is predominantly driven by co-slip. Appendix B suggests that viscoelastic relaxation may exist but contributes relatively little. However, analyzing only 11 months of post-earthquake deformation may underestimate the role of viscoelastic relaxation, which could manifest over longer periods. Therefore, it is recommended that the authors incorporate observational data spanning a longer timeframe to comprehensively assess the contribution of viscoelastic relaxation.  
8. In the co-slip model, the authors tested single-fault, double-fault, and triple-fault models, selecting the latter based on RMSE. However, assuming identical depth, width, and slip momentum for all fault segments may deviate from reality. Uncertainty analysis of the inversion results is suggested to evaluate the reliability and error range of the model. Moreover, the physical plausibility of the three-fault model is not fully demonstrated. Do the three fault planes align with regional structures (e.g., Madian faults or branch faults)? Could they result from data noise or overfitting? It is recommended that the authors verify the rationality of these fault segments using more detailed geological information.  
9. The paper mentions that the January 29 aftershock resulted from the rupture of two faults and compares the findings with those of Qiu (2024). However, the geological significance of the two sets of results, particularly the opposing fault dips, is not fully explained. A deeper analysis of the correlation and activity characteristics of these two faults, as well as their primary-secondary relationship and influence on post-earthquake deformation, is warranted.  
10. The need for further validation through GNSS or geological field data is noted, but the extent to which current solution uncertainties impact conclusions remains unclear. It is suggested that the structural implications of the two solutions (this paper and Qiu's model) be clarified in the discussion. For example, does the difference in the dip angle of Fault F1 reflect varying development patterns of blind thrust fault front branches?  
11. Three mechanisms of post-earthquake deformation (co-slip, viscoelastic relaxation, and pore-elastic rebound) are mentioned in the introduction, yet the text focuses exclusively on co-slip and viscoelasticity without analyzing the potential contribution of pore-elastic rebound, especially in cases involving fluid effects in the shallow portion of blind thrusts. It is recommended to include a brief evaluation of pore-elastic rebound in the discussion section or explicitly limit the study's scope to co-slip and viscoelasticity in the introduction to avoid misinterpretation.  
12. Appendices A and B provide supplementary model results but do not fully leverage the data to deepen the discussion. It is suggested that the results of Appendix A be referenced in the main body to compare spatial residual distribution differences between the two models and infer more reliable aftershock fault geometries in conjunction with geological context.  

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Dear Reviewer,

Thank you very much for your kind consideration and valuable suggestions! We responsed to your suggestions point-by-point.

Please see the attachment.

Best regards!

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript addresses the early post-seismic deformation of the 2024 Mw 7.1 Wushi earthquake, employing InSAR data analysis, fault modeling, and Coulomb stress changes. Overall, the manuscript is clear, and the study is timely and relevant. However, several specific areas require attention to enhance the clarity and scientific rigor.

Line 24: Contradiction in earthquake magnitude (Mw 7.0 in Introduction, Mw 7.1 elsewhere). Clarify the correct magnitude throughout the manuscript.

Lines 51-53: The statement regarding crustal shortening rates ("~19-20 mm/a") needs a clear reference or additional detail to justify this rate.

Lines 67-68: The slip rake ("49.9°") requires mentioning uncertainties or a citation supporting this precise measurement.

Lines 83-85: Provide reasoning or a reference to justify the selection of "7 looks in the azimuth and 21 looks in the range direction." This choice influences data resolution.

Lines 86-87: Clarify if the tropospheric delay correction completely addressed potential atmospheric disturbances or residual noise remained.

Lines 121-123: Clarify why significant deformation is apparent only in ascending data compared to descending data regarding the aftershock. Is this simply due to geometry or processing biases?

Lines 125-128: Consider explicitly mentioning the reason for separating deformation analysis into two time periods and its scientific rationale.

Lines 153-155: The choice of a two-fault model is briefly justified. Clarify further if geological evidence supports this scenario or if it’s solely based on InSAR analysis.

Lines 158-165: Include uncertainties or confidence intervals for best-fitting fault parameters clearly and directly in Table 1, not just in a separate percentile format, which can be confusing.

Lines 189-193: State explicitly if geological or seismological evidence supports the three-fault afterslip scenario or if this finding solely relies on modeling.

Lines 206-211: Clarify the choice of subdividing only the largest fault segment into patches. Why were the other segments not subdivided similarly?

Lines 214-216: Provide uncertainty or standard deviation for Coulomb stress values to reflect modeling confidence clearly.

Lines 223-229: Clearly state that the two-fault scenario is an assumption due to discrepancies between observed deformation and seismic catalogs. Also, explicitly highlight that geophysical or field data could further validate these results.

Lines 239-242: The final recommendation for additional GPS or field geological data is critical. Strengthen the suggestion by mentioning the type of specific additional data (GPS, geological trenching, or borehole data) that could resolve this issue.

Lines 248-256: Provide context for why the afterslip is relatively small compared to other earthquakes listed. Possible geological or rheological factors should be briefly discussed.

Author Response

Dear Reviewer,

Thank you very much for your kind consideration and valuable suggestions! We responsed to your suggestions point-by-point.

Please see the attachment.

Best regards!

Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

I must say that the authors have worked very hard to address all my comments and which is a clear reflection in the quality of the manuscript. The work has significantly improved and I have no further comments. I recommend its direct accaeptance.