Coseismic Deformation Field Extraction and Fault Slip Inversion of the 2021 Yangbi M_W 6.1 Earthquake, Yunnan Province, Based on Time-Series InSAR

Round 1

Reviewer 1 Report

The aim of the paper of Li et al.. is to demonstrate the effective improvement in the estimation of the coseismic deformation in using pre- and post-seismic time series rather than a single interferrogram; to do this they show the relative data / model / residual comparison in figure 8. However, looking at the panels of the residuals, I cannot see this clear improvement, or at least this is not appreciable from this figure. The displacement values ​​are too small to allow such an improvement to be assessed. In my opinion the authors should make and show a more quantitative analysis (for example in terms of rms) to highlight an analysis of this type. Probably this comparison is not particularly appreciable in this particular case study (the maximum coseismic displacements are too small, 6 and 7 cm for the two orbits) and the residual analysis alone is not sufficient. In my opinion, this is a strong point of weakness of the article. I suggest either to use a new case study with greater displacement or to show a quantitative comparative analysis (in addition to showing residuals).

For this reason, I suggest a major revision.

I have also the following minor points to be better fixed:

• insert the citation of the figure 1 to the line 48;
• Line 73 “Time-series InSAR was introduced in the late 20th century” insert bibliography about this;
• Figure 1: use different colours for aftershock and foreschock for a better discriminating;
• Line 273: It should be ‘coseismic’ and ‘postseismic’;
• Line 335:’ A positive value of LOS displacement indicates that the surface deformation is moving towards the satellite, which manifests as a surface uplift’. This is partially true, because a positive LOS displacement may be also the effect of a E-W horizontal displacement;
• Table 2: What does 2.50 % and 97.50 % mean?

Author Response

Thank you for taking time out of your busy schedule to review the manuscript. We have carefully read the thoughtful comments from you and found that these suggestions help us improve our manuscript. Now we have carefully corrected and replied the manuscript for this revision. The revision instructions are as follows. Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

In the manuscript “Coseismic Deformation Field Extraction and Fault Slip Distribution Inversion of the 2021 Yangbi MW 6.1 Earthquake, Yunnan Province, Based on Time-Series InSAR”, the authors provide a new SAR processing chain to retrieve coseismic displacement field from Time-series InSAR analysis. The authors claim that such an approach is more effective in mitigating atmospheric, orbital and topographic errors on the unwrapped coseismic displacements. To prove their claims, they process S1 SAR data imaging the coseismic displacement field caused by the Mw 6.1 earthquake that happened in May 2021 in the Yangbi region and invert the deformation signal to retrieve the source geometry.

Main comments:

• Overall, the manuscript is well written and organized, with only a few errors highlighted in the minor comments. I’m not an InSAR processing expert, so I cannot judge the reliability of the proposed processing chain with respect to the available classical InSAR techniques. To my opinion, the authors should improve the description of the processing chain in the Methods section (e.g., the Flowchart in Figure 2 is unclear and incomplete). Moreover, the manuscript must be focused mostly on the description and validation of the proposed processing chain instead of describing the earthquake deformation and fault geometry, which is well-known since it has been already published by Wang et al., 2021 (Wang, Y.; Chen, K.; Shi, Y.; Zhang, X.; Chen, S.; Li, P.; Lu, D. Source Model and Simulated Strong Ground Motion of the 2021 Yangbi, China Shallow Earthquake Constrained by InSAR Observations. Remote Sens. 2021, 13, 4138. https://doi.org/10.3390/rs13204138). Both the results and discussion sections need a substantial review to highlight the advantages (and weaknesses) of the proposed new approach.
• Regarding the results, here the feasibility of the proposed processing chain is not obvious. Indeed, a proper assessment of the validity of a new approach with respect to classical approaches requires its application to synthetic data, i.e., data that are artificially generated and where all the different contributions to the signal (i.e., atmospheric, topographic, true ground displacement) are well known. On this dataset, the authors should apply classical and newly proposed approaches to quantitatively assess the differences. Currently, the results show a qualitative comparison between unwrapped interferograms in Figure 4, where each panel has different scale bars, such as it is impossible to judge the validity of the proposed approach. The assessment with synthetic data is mandatory for the future acceptability of this manuscript.

The inversion procedure is too long and does not provide further clues on the effectiveness of the proposed processing approach. Moreover, these results are not compared with those obtained by Wang et al., 2021 with the same SAR dataset.

• The discussion section must deeply describe the novelties and weaknesses of the proposed approach, even with respect to novel approaches available to mitigate errors in the interferograms, such as the GACOS service (http://www.gacos.net/).

In summary, the manuscript has good potential but needs major revisions in order to be acceptable for publication.

 

Minor comments:

Line 54: What do you mean by “large magnitude”? According to the estimated moment magnitude, such an earthquake can be classified as a moderate magnitude

Line 58: “Such information is important for earthquake risk assessment and prevention”. Please explain how.

Line 76: add “.” Between “phase” and “Although”

Line 129 and Figure 1: It is not a geological map, please add relevant information and zoom on the area of interest. Separate foreshocks and aftershocks with different colours

 

Line 159: substitute “pentagram” with “star”

Line 335-339. Such a statement is not correct since positive and/or/negative los displacements are due to the combination of both horizontal and vertical ground movements and do not mean uplift or subsidence.

Figure 4: Color scales in Figure a-b and c-d must be the same

Figure 5 is neither described nor discussed

Line 486: “descending”

Author Response

Thank you for taking time out of your busy schedule to review the manuscript. We have carefully read the thoughtful comments from you and found that these suggestions help us improve our manuscript. Now we have carefully corrected and replied the manuscript for this revision. The revision instructions are as follows. Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Recommendations for improvement

Paper title. Delete “Distribution”.

83. Replace “by Hooper et al. in 2004” by “[10]”.

Figure 1. Plot foreshocks and aftershocks with different colours.

404. Improve as next: “….the strike-slip component…the dip-slip component..”.
405. Improve as next: “…the fault mechanism is consistent with a large right-lateral strike-slip component and a small thrust component”.
406. Improve as next: “the fault mechanism is dominated by a right-lateral component”.
407. The figure 1018 is not correct, it is 10 to power 18.

In Section 3 (Material and Methods) the authors are referring to the DEM (Digital Elevation Model) used. The authors should provide the data source either in the text or in the section Data Availability Statement.

In Section 4 (Discussion), the first paragraph (lines 489-506) does nor represent a discussion. Instead, it is a summary of results and how they were obtained. I propose to create a new Section 5-Conclusions and move that paragraph in the new section.

Author Response

Thank you for taking time out of your busy schedule to review the manuscript. We have carefully read the thoughtful comments from you and found that these suggestions help us improve our manuscript. Now we have carefully corrected and replied the manuscript for this revision. The revision instructions are as follows. Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Accepted in the present form

Reviewer 2 Report

There are no comments for the authors