Characterizing Micro-Displacements on Active Faults in the Gobi Desert with Time-Series InSAR

Round 1

Reviewer 1 Report

This paper aims to identify and map the micro-displacement along active faults by using PSInSAR technique, which is not a relatively new method in the study of tectonic movements. InSAR and PSInSAR have been widely used in characterize the movement of active faults. Several issues should be addressed before publication.

• In the methodology, the introduction of InSAR technique is basic and simple. The details are required to describe the PInSAR process, including the PS point selection, the phase unwrapping, the correction of DEM error, orbital error and atmospheric delay.
• When introducing the estimation of vertical and horizontal displacement, the equations may not be appropriate. Especially in equation 4., do the both d_los and delta_R represent the displacements in LOS direction? I suggest the authors rephrasing the description part of 3D displacement estimation.
• The deformation rate maps in Figure 6 and 7 are quite noisy. Since there is no ground measurement to validate the displacements by InSAR, it is hard to judge whether the deformation variation is caused by real ground movements or decorrelation noise and atmospheric artifacts.
• Normally, the maximum precision of InSAR technique is millimeter level. However, in this paper, the range of deformation rate is limited within 1 mm/year, which exceeds the monitoring capability of InSAR. From the time-series displacements in figure 9, the deformation rate is smaller than 0.5mm/year. In my eyes, the deformation condition in this area is very stable. We cannot conclude that the tectonic processes are active.

Author Response

Dear Reviewer, 

 

Many thanks for your comments, which is very constructive and positive to improve our work. Please see the attachment, here is our point-by-point response. 

 

Best wishes,

Zixiao 

Author Response File: Author Response.docx

Reviewer 2 Report

Reviewers' comments:

This paper presents the study on the investigation of the small-scale tectonic activity at Jiujing region in Beishan, Northwest China utilizing the Persistent Scatterer (PS) InSAR. It is an interesting paper; however, it is suggested that the article in present form is not recommended for the consideration of the acceptance in the journal of Applied Sciences due to the following reasons.

Several important issues remain to be clarified as follows.

1. Since the main goal of this paper is to utilize the time-series InSAR to characterize micro-displacements on active faults in the Gobi Desert, reviewer's suggestion to authors is to improve the INTRODUCTION section. Please compare the cons and pros for various monitoring techniques for mapping ground deformation which would clear up the ultimate goal and benefits of the PS InSAR. In addition, it is recommended to give an overview of each section of the manuscript at the end of the introduction.
2. The legend cannot be clearly identified in Figure 1. The quality of the figures is required to be improved. It is suggested that the resolution of all the figures in the manuscript should be increased.
3. Please clearly define the definition of BS01, BS02 and BS03 in Figure 3. The legend in Figure 3 should be improved.
4. In the Methodology section, the symbols used in the equation are not consistent in the symbols defined in the content. For example, all the symbols including the Φ, Φdem, Φatm, Φorb, and Φscat are in bold front. However, the above symbols become in italic front in the content. Usually, the basic definitions of the vectors or the matrix are written using bold fronts.
5. The calibration and validation of InSAR data over research areas with slope variations should be carried out in Section 3.3. The authors should explain the reason why Equation (4) are adopted for the error measures instead of commonly used absolute error, relative error, or root mean square error.
6. There is typo in Figure 5. “Footwall wall” should be “Footwall”. Additionally, the vertical and eastward deformation along the fault plane cannot be clearly identified.
7. Figures 10, 11 and 12 depict the vertical displacement along three different cross sections in Figure 8. However, the location of the above cross sections is not defined in Figure 8.
8. Please connect the significant results of the main points in the Conclusion section. Even if the findings were explained, it is necessary to describe a more robust discussion of the achieved results, in order to better explain the strengths of the proposed method respect to other approaches and its possible limits. The discussion should be inserted in a “Discussion” section, before “Conclusion” section.
9. There are no page numbers in this manuscript. It is suggested that authors must use the template provided to prepare their manuscript. 

Author Response

Dear Reviewer, 

Many thanks for your comments, which is very constructive and positive to improve our work. A point-by-point response has been provided, please check the attachment. 

Best wishes,

Zixiao 

Author Response File: Author Response.docx

Reviewer 3 Report

Dear editor,

This paper applies the time-series InSAR method to better explore the vertical and horizontal displacements of faults in Beishan, China. The authors also explained the spatial and temporal complexity of displacements in many details. I have serval criticisms, which hopefully would help improve the quality of paper.

• I suggest giving more information about the PS-InSAR method. For example, how did you determine the threshold of cohesion (Phase Unwrapping Error)? I found some discussions in part 4.4, but clearly more quantitative analysis would make the results convincing.

 

• At end of part 1, the aim is to ‘develop a new approach’, did you improve the method of Ferretti et al., 2001 [33], what is the novelty in your method. Pls clarify it.

 

• Improve the quality of figures.

 

 e.g. uniform the text size in Figure 5.

 

Combine Figure 17, the google earth subset into other figure, as it is very strange to make google earth map without anything added on it as a figure for a scientific paper.

 

Pls indicate how to calculate the error bar in figure 9 (std?), again pls combine figure 9 a, b ,c , d together, otherwise it looks messy.

 

• Pls improve the English writing and logistic. ( add line numbers for others to review)

 

e.g. In abstract, the expression of ‘PS InSAR should be’ seems strange.

Citations in paragraph 3 of introduction lack linkage sentences and logistic connections.

 

Overall, I suggest a moderate revision.

Author Response

Dear Reviewer, 

 

Many thanks for your comments, which is very constructive and positive to improve our work. Please see the attachment, here is a point-by-point response to your comments. 

 

Best wishes, 

Zixiao 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The revised paper still does not resolve the problem about the capability of InSAR deformation detection. The difference of deformation rate smaller than 1mm/year has exceeded the maximum monitoring capacity by InSAR. So, in this study, the movement of active faults based on InSAR measurement is insignificant and unconvincing, probably due to random noise or uncorrected turbulent delay. Based on the deformation map in this paper, deformation condition in Jiujing region is believed to be stable. Therefore, a much longer observation period (e.g., 8 to 10 years) is required to demonstrate the conclusion in the paper, instead of 2.5 years’ time period. 

Author Response

Dear Reviewer, 

Many thanks for the comments. The following attachment is our response. Please check it. We hope it can address your concerns. 

Best wishes, 

Zixiao  

Author Response File: Author Response.docx

Reviewer 2 Report

1. The symbols used in the equation are still inconsistent in the symbols defined in the Methodology section. For example, ΔR is in italic front at line 162 in page 8.  However, ΔR becomes in bold front in Eq. 2 in page 8.
2. Are the symbols including the Φ, Φdem, Φatm, Φorb, Φscat, and ΔR scalars or matrices? If the above symbols are defined as scalars, these symbols should be written in italic fronts instead of bold fronts.

Author Response

Dear Reviewer, 

Many thanks for the comments., which is very helpful to improve our work. The following attachment is our response. Please check it. 

Best wishes, 

Zixiao  

Author Response File: Author Response.docx

Reviewer 3 Report

The authors have made substantial modifications to address my preview concerns.

My last concern is about the accuracy of displacement. For example, the value at region JJ26 is 0.04 ± 0.75 mm (Figure 7), also in Figure 9, the standard deviation (STD) is much higher than the average value. It is scary to see the STD is 20 times higher than the mean value in a scientific paper.

I have 2 possible suggestions for authors to consider. 1) resize and redefine the blocks to minimize the STD, 2) use filter algorithms to reduce data noises. Maybe there are better methods, but pls make sure the results are reasonable.

Author Response

Dear Reviewer, 

Many thanks for your comment, which is very helpful to improve our future work. Please check the following attachment, here is our response. 

Best wishes, 

Zixiao Wang 

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

The revised manuscript has addressed my previous concerns. The manuscript can be accepted after a map correction. In the revised manuscript, the China map in figure 1 is wrong, please correct it. I recommend the authors can the download the study area map from official website.

Author Response

Dear Reviewer, 

 

Many thanks for the comments. The China map in Figure 1 has been updated. Please do let us know if you need any further information. 

 

Best wishes, 

Zixiao 

Reviewer 2 Report

Since the authors have revised the manuscript, it is suggested the manuscript can be accepted in current form.

Author Response

Dear Reviewer, 

Many thanks for that! 

Zixiao