Dear Authors,

Your manuscript "Active tectonics of the onshore Hengchun Fault using UAS DTM combined with ALOS PS-InSAR time series (Southern Taiwan)" (nhess-2017-55) has been assessed by two reviewers. You have also provided feedback during the NHESS open discussion. Based on this discussion, I would like to inform you that you should carry out some essential, major revisions suggested by the reviewers and editor before being published in NHESS. The comments by the editor follow this message.

Once you have made the necessary corrections, please submit a revised manuscript with a point-by-point response. Also please highlight all changes made when revising the manuscript. Please ensure you include a detailed rebuttal of any criticisms or requested revisions that you disagreed with. Please also ensure that your revised manuscript conforms to the journal style.

Please note that this editorial decision does not guarantee that your manuscript will be accepted for final publication in NHESS. A decision will be made after the revised version is submitted and evaluated by the same or further reviewers.

We look forward to receiving your revised manuscript soon.

Best regards,
yuichi hayakawa

****

General comments:
This study explores the characteristics and activities of a fault group in southern Taiwan by the combination of approaches using UAS, InSAR, GNSS, and leveling. UAS is used to identify the fault traces, while the others are used to detect motion of the active faults. A schematic model of the fault is finally proposed. The objectives of the study are clear, and they are accordingly examined by the approaches above, but to my concern, the manuscript needs further revisions. The main concerns are below:

1) The structure of the paper needs to be reorganized.
The current sections 2, 3, and 4 are provided according to the methodological topics (UAS, field mapping, and InSAR), but each is the mixture of methods and results (and sometimes general facts by previous studies). The method and result would be better described separately for the clarity of the paper. I would recommend making separate sections of Methods, and Results, under which the individual topics (UAS, field mapping, InSAR etc.) are provided. The general geology and geomorphology (that are not derived from this study) can be described in Study area before Methods.

2) The originality of this study needs to be clarified.
As noted in the specific comments P4 L26 below, the originality of the identification of a mud volcano needs to be clarified. Also, there is an inconsistency of the extent of the study area in Figures 1, 8 and 2, 6, 9. Please confirm that the work outside of the area of interest in Figure 1 is actually carried out by the authors.

Specific comments:
P1 L14: “Characterize” --> “Characterizing”; including this point, the English should be better further corrected throughout the manuscript.
P2 L5: “see Fig. 1” --> “Fig. 1”
P2 L10: Clarify or remove “by previous authors”. Also, use “e.g.,” instead of “; among others”
P2 L11: Avoid using “…” (also for the other portions in the manuscript)
P2 L20: Explain “PS-InSAR” here. Particularly, the definition of “PS” is missing throughout the manuscript (c.f. P5 L21, 22).
P2 L23: “few” could be “a few"
P2 L27: “widly” --> "widely"
P3 L4-: Insert a space between the number and unit (e.g., 8cm --> 8 cm).
P3 L8: "extracted from airborne LiDAR dataset" Please provide details of this procedure including the location (distribution) and characteristics (what sort of materials) of the ground control points, because this is crucial for the accuracy description. Also, please clarify what does "the open bar ground area" (L10) stand for. Is it a small area for the comparison, or a wide area covering entire dataset? If the former, how is it close to the GCPs?
P3 L27: "e.g.," instead of "among others"
P4 L5: "work in progress" This wording often appears in this manuscript, but it may not be suitable to regard it as something like a citation. Better to be removed and clarified as a future issue.
P4 L26: Please clarify how the mud volcanoes were identified. If they are based on some literature (e.g., Giletycz 2015, NCU dissertation), the original work should be properly taken into account and cited.
P5 L26: Be consistent to use the shortened term "HeF": if this is used, it should appear on the former side of this manuscript and thereafter the use of "Hengchun Fault" should be avoided. However, I personally think "HeF" may not be necessarily introduced in the manuscript text (better to be in the Figures only). The term "Hengchun Fault” is not so long.
P6 L1: The methodological description of “GPS measurement” is missing.
P6 L28: “StaMPS” or “STAMPS”? Be consistent.
Figure 1 caption: “Figure 1a:” --> "(a)", also for b and c.
Figure 1 GPS station: The displacements of the HENC GPS station indicates an uplift in Figure 1, but why is that in Figure 8 negative? If Z component is positive (uplift), the LOS component should also be positive. Please clarify together with the methodological description of the GPS measurements as suggested above.
Figure 1 Area of Interest: The area of interest shown in Figure 1 seems to correspond to that of Figure 8, but in Figures 2 and 6 the study area is much wider including the southern coast. In particular, the mud volcano is located out of the range of the area of interest in Figure 1, and it is unclear whether this was investigated by the authors or derived from something else (see the comments for P4 L26). Moreover, the whole leveling line 2 and the eastern half of line 1 are apparently out of the extent of Figure 8, and it is unclear how the PS values were obtained for these areas. These inconsistencies should be clarified.
Figure 2: Put (a) and (b) in the panels. Avoid using “Right” or “Left” in the caption.
Figure 3: Put (a)-(i) in all the panels. The scale and north direction are missing.
Figure 4: Put (a)-(c) in the panels. Better to show the photo location and direction in Figure 2.
Figure 5: The red lines are too thick to prohibit viewing the cracks in the photo. Can they be thinned or set higher transparency?
Also, “Fang-Shan village” is not shown in Figure 1.
Figure 6: It would be better to show the rectangular extents of the example areas of Figure 3 (same as in Figure 1). Red (2) and pink (8) lines are hard to differentiate.
Figure 8: If the current A and B show the same displacements, the left one can be omitted. The schematic model of LOS (graphic description including satellite) should be placed in a separate panel, and the flight direction and LOS could be placed in the map panel (like Figure 1).
Figure 9: Put (a)-(c). Explain in caption what the pink area indicates.

Comments to the Author:

Dear Authors,

Your revised manuscript "Active tectonics of the onshore Hengchun Fault using UAS DTM combined with ALOS PS-InSAR time series (Southern Taiwan)" (nhess-2017-55) has been assessed. Following the reviewers’ comments, I would like to inform you that further essential revisions are necessary before being published in NHESS. Please carefully assess the comments by the reviewers and editor below.

Once you have made the necessary corrections, please submit a revised manuscript with point-by-point responses. Also, please highlight all changes made when revising the manuscript. If any, ensure you include a detailed rebuttal of any criticisms or requested revisions that you disagreed with. Please also ensure that your revised manuscript conforms to the journal style.

Please note that this editorial decision does not guarantee that your manuscript will be accepted for final publication in NHESS. A decision will be made after the revised version is submitted and evaluated by reviewers.

We look forward to receiving your revised manuscript soon.

Best regards,
yuichi hayakawa

****

Reviewer #1

1. The main two resulting products are newly interpreted Hengchun Fault in Fig. 6 and the offset of mean LoS velocities between eastern and western part from the Fault. And the authors make an assertion of the active inter-seismic tectonic deformation model of the Fault.

2. However, the newly interpreted Fault plays a minor role in the proposed tectonic deformation model. Even if detailed distribution of the Fault is revealed using UAS products, the authors do not explain how the distribution effectively works in order to propose the tectonic deformation model nor mention how the distribution differentiates the new model from the previous models. Relation between the detailed interpretation of the Fault and the proposed model is vague.

3. The authors made a crucial mistake that LoS change stands only for vertical component of deformation, i.e., uplift and depression. LoS changes include not only vertical component but also horizontal component of the deformation, however, the authors do not explain enough why vertical component should be paid attention and why horizontal component is not considered.

4. Fig. 4 infers left lateral movement and Fig. 5 infers EW compression, however, the reviewer could not catch the relation between the newly interpreted Fault and such the field observations. Furthermore, the authors did not mention how the horizontal component of the deformation is interpreted from the LoS change velocity to propose the new model.

5. Therefore, the reviewer thinks that it is difficult for the reviewer to judge the acceptance.


Reviewer #2

In this study, Deffontaines and others use the UAS derived DTM and geodetic measurements to investigate the morphology, crustal deformation pattern and fault creep/locking characteristics of the Hengchun area in the southernmost part of Taiwan. Their finding shows the trace and activities of the Hengchun fault, which is important for the purpose of natural hazard investigation especially due to the nearby nuclear power plant. The focus of this manuscript is clear, and I think that with moderate revision this manuscript should be publishable in this journal.


Comments:

Somewhere in discussion could you emphasize the improvement of using the UAS derived DTM than the 40m DEM? I cannot easily see what can only be resolved with using the new DTM.

Page 2
Line 10: I am not sure whether using exclamation point is the best choice of punctuation in this sentence.

Line 13: Indicate the power plant in Fig. 1.

Line 21: Write down the full name of InSAR when first mentioned it.

Page 3
Line 8: Delete “…”

Line 9: “Eighteen” instead of “18” in the beginning of a sentence.

Page 5
Line 12: “in” Figure 6

Line 21: Need a full citation of Chen’s report.

Section 4: Where is the reference point for the PS analysis? Please indicate the location in Fig. 8.

Page 6
Line 1: might be submitted to → might be subject to

Line 16: Dealing with the Kenting → “Regarding the Kenting” or “With regard to Kenting”

Lines 25-26: Do you mean that the GPS LOS velocity is converted from leveling measurements and GPS horizontal measurements? How about leveling measurements in Fig. 9? Is it showing leveling vertical or have you converted it into LOS as well? How?

Page 7
Lines 14 and 17: Please avoid using “…”

Lien 26: How is the creeping value estimated? If you refer to the difference of surface velocity between the west and east of the Hengchun fault (in stead of creeping along the fault), I will suggest saying “difference in interseismic velocity between west and east of the Hengchun fault with a value of 8 mm/yr”. Based on the figure it looks like 8 mm/yr instead of 0.8 mm/yr.

Page 8
Lines 6-8: I know this is a schematic model figure, but could you infer the dip angle along strike of the Hengchun fault? Is it a high or low angle fault?

Line 12: present both left-lateral strike-slip and thrust dip-slip components such as ...

Line 13: Could you provide more examples of faults with this oblique component property?

Line 14: Please avoid using both “cm” and “mm” in the same paper.

Lines 16-18: I think this comparison is a bit unfair, as the InSAR derived velocity is in LOS, whereas vertical from marine terrace dating results. If the authors know the fault dip angle they should try fault inversions using different datasets, and then compare the inferred slip in geologic and geodetic time scales. Also I suggest saying “geodetic slip rates” instead of “instantaneous slip rates”.

Page 9
Line 14: PS km-2

Line 16: the highly dipping Hengchun Fault → the Hengchun Fault with high dip angle

Line 16: Choose either “interseismic” or “inter-seismic” throughout the manuscript.

Line 23: due to (1) xxx, (2) xxx.

Line 23: to the low fault dip angle deduced from …

Line 27: Suggest using “Nevertheless” than “Anyway”

Figure 3:
Line 9: I cannot find NPP and MV in the figure.

Figure 8: Looks like the PS points in the southernmost part are not plotted, as they are shown in Fig. 9 in comparison with leveling measurements.

Figure 9: How the InSAR error bars were estimated?

Figure 10: Is the label (2) needed in this figure?

Figure 11: Is this figure showing offset between the hanging wall and the footwall? Where is the GPS measurement (HENC?) relative to?



Editor #1

As the Reviewer #1 suggests, the current paper does not fully demonstrate the relationships among the UAS-derived geological interpretation of the fault, independent InSAR LoS interpretation, and the inferred deformation model of the fault. I am not aware of the “classical geological way”, but the mixture of methods/results/interpretations for each topic in the current manuscript seems to make it difficult for readers to figure out what is the new point of this study. To avoid this, I would recommend to restructure the entire manuscript (as I originally suggested), or at least, make clear steps in each section of different methods.

Moreover, as listed below, there are too many issues that have not been correctly addressed in the authors' revision. It is necessary to clarify all the issues.

1) "we confirm herein our interest towork in the NHESS paper on the whole onshore Hengchun Fault area that is covered bythe UAV survey. For instance, the leveling lines 2 (Fig 9) confirm the LOS INSAR displacement of the Hengchun Fault in the southern part.”

>> This is not true, as the area of interest of InSAR shown in Fig. 1 is apparently different from the area of leveling survey shown in Fig. 9. Eastern half of both of the leveling survey lines are out of the range, but still values of LoS are given along the line (Fig. 9b, c).

2) P2 L10: Clarify or remove “by previous authors”. Also, use “e.g.,” instead of “; among others”
Done

>> When “e.g.,” is used, “etc.” is unnecessary.

3) P2 L11: Avoid using “…” (also for the other portions in the manuscript)
Done

>> Not corrected. It remains in many places throughout the manuscript.

4) P2 L20: Explain “PS-InSAR” here. Particularly, the definition of “PS” ismissing throughout the manuscript (c.f. P5 L21, 22).
Done

>> Still missing is the explanation of InSAR (at least, it should be spelled out).

5) P4 L5: "work in progress" This wording often appears in this manuscript, but it may not be suitable to regard it as something like a citation. Better to be removed and clarified as a future issue.
We removed the (only) two "work in progress" written in this paper…

>> Not corrected. There still remains this wording in the manuscript.

6) P6 L1: The methodological description of “GPS measurement” is missing.
We precise the GPS data used to validate our PS-InSAR results.

>> The details of the “GPS measurement” is still unclear. The authors seemed to use data from static GNSS stations for revealing displacements, as well as kinematic GNSS measurements for GCPs, but these details are not properly provided (some missing and some unclear). Also, detailed description of airborne LiDAR is missing. As noted above, clear descriptions of the methodologies, as well as their results and interpretations, are necessary to be provided separately.

7) Figure 1 caption: “Figure 1a:” --> "(a)", also for b and c.
Done

>> Not done.

8) Figure 1 Area of Interest: ... Moreover, the whole leveling line 2 and the eastern half of line 1 are apparently out of the extent of Figure 8, and it is unclear how the PS values were obtained for these areas. These inconsistencies should be clarified.
Our study area correspond to the onshore Hengchun Fault covered by the UAS survey acquired and shown in Fig. 2. Some figures present a smaller extension due to potential political conflicts with sensitive Taiwan infrastructures (Nuclear PowerPlant N°3).

>> This is not the point, as noted above at 1).

9) Figure 4: Put (a)-(c) in the panels. Better to show the photo location anddirection in Figure 2.
Done

>> Not corrected. Also, Figure 2 shows the photo location but the direction is unclear.

10) Figure 5: … Also, “Fang-Shan village” is not shown in Figure 1.
GPS data was and is still given in the legend.

>> It is never seen anywhere else in the manuscript.

11) Figure 6: It would be better to show the rectangular extents of the example areas of Figure 3 (same as in Figure 1). Red (2) and pink (8) lines are hard to differentiate.
This important figure 6 is difficult to read and we would like to avoid to add too many things on it not directly linked to the thematic... that is why we have chosen to draw the quadrangle on Fig. 2.

>> Still I cannot clearly identify the pink (8) lines.
I understand putting less information is better, but still do not understand the correspondence between the coverage by the UAS-derived data and that by the “morphostructural map”. Does the western margin of “9: Hengchun valley alluvial and marine deposits” overlaps with the area? If not, how was it mapped?

12) Figure 8: If the current A and B show the same displacements, the left one can be omitted. The schematic model of LOS (graphic description including satellite) should be placed in a separate panel, and the flight direction and LOS could be placed in the map panel (like Figure 1).
Ok we remove the Fig 8A, we redraw that figure

>> Panel A was removed but the other points were not addressed.

Dear Authors,

Your manuscript "Active tectonics of the onshore Hengchun Fault using UAS DTM combined with ALOS PS-InSAR time series (Southern Taiwan)" (nhess-2017-55) has been assessed by the reviewers. They raised several critical issues that need to be fixed before publication. Based on these comments, and my own assessment as Editor (comments attached below), I would like to inform you that it is potentially acceptable for publication in NHESS, provided that you carry out essential revisions suggested by the reviewers.

Once you have made the necessary corrections, please submit a revised manuscript with point-by-point responses to both reviewers, and highlight all changes made when revising the manuscript. Please ensure you include a detailed rebuttal of any criticisms or requested revisions that you disagreed with. Also, ensure that your revised manuscript conforms to the journal style.

Please note that this editorial decision does not guarantee that your manuscript will be accepted for final publication in NHESS. A decision will be made after the revised version is submitted and evaluated by the same or further reviewers.

We look forward to receiving your revised manuscript soon.

Best regards,
yuichi hayakawa

****

Comments by Editor

Response #1-3: Fig. 10 covers wider area than the areas of interest shown in Figs. 1, 2, 7, and 9. The eastern half in Fig. 10 could therefore be eliminated.

Response #1-8: Even if the focus of this paper is not on GPS (I would recommend this to rephrase as GNSS, a more generic term, if some other satellite data are used such as GLONASS) itself, the only one reference is insufficient to correctly represent the methodology. Not necessarily to be too detailed, but the authors can provide some more details for an objective validation.

Response #1-12,13: Fang-Shang (Figure 6 caption) or Feng-Shang (Figure 1 caption)?

Response #1-16: Please provide the satellite orbit path and the line of sight directions projected on the map.

Dear Authors,

Your revised manuscript has been assessed by the reviewers. Based on their reports, and my own assessment as Editor, I would like to inform you that it is potentially acceptable for publication in NHESS, provided that you carry out some essential revisions.

Once you have made the necessary corrections, please submit a revised manuscript with point-by-point responses to the comments, and highlight all changes made when revising the manuscript. Also, ensure that your revised manuscript conforms to the journal style.

Please note that this editorial decision does not guarantee that your manuscript will be accepted for final publication in NHESS. A decision will be made after the revised version is submitted and evaluated.
We look forward to receiving your revised manuscript soon.

Best regards,
yuichi hayakawa

----

The authors have provided their revised manuscript following the reviewers’ suggestions.
However, before being accepted, there are some reservations as listed below.

Further corrections needed for the proposed responses:

* #1-3, #1-10, and #1-11: There may be some misunderstandings. The problem has been the inconsistency among the coverage areas for the data provided by InSAR and leveling surveys. If the InSAR data is available for the eastern area as the authors suggest in their response (this was not clear in the manuscript), Figure 1 should show the entire extent of the area of target, including the eastern side (like the case for the current Figure 3a). It is also necessary to explicitly indicate the extent of available data for InSAR, like that for the UAS data area. Figure 9 should also be widened to include the eastern side, together with the PS-InSAR plots and leveling lines. If this is achieved, current Figure 10a becomes unnecessary (i.e., all the locational contents in Figure 10a can be integrated into Figure 9).

* #n1-8: I do agree with the authors that too many details are unnecessary for the cited work. However, one may not be able to instantly read the cited paper, and it should be helpful and more scientifically sound if some basic descriptions of the method (including measurement type (static I guess), accuracies, temporal frequencies, measurement periods, etc.) are provided.

* #n4-33: Please revise the newly added Figure 3 with regard to the better interpretation of the geological components (geological boundaries, fault lines, and terraces). It is still unclear how these high-resolution images contribute to the better interpretations of the geology in this area, although this is partly shown in the next Figure 4. Therefore, please provide some interpreted lines on these high-resolution maps in Figure 3.

Some other editorial comments:
1. Abstract: It is better to remove citations in Abstract (P. 1, L. 19).
2. P. 1, L. 23 and 33: Please spell out GPS.
3. P. 2, L. 1: Please provide the unit in mm/y.
4. P. 2, L. 19 and followings, on the terminology for DTM, DSM, and DEM: There seem mixed uses of these three words. In general, DEM (digital elevation model) is a generic term, including the filtered DTM (digital terrain model) showing bare land and surficial DSM (digital surface model) before filtering/removing ground objects. Photogrammetric approaches can usually provide only DSM (except some cases), while airborne lidar can provide both of DTM and DSM. In particular, UAS usually generates DSM only. If DTM is generated from UAS-derived photogrammetric data, there should be some specific algorithms to filter the raw point cloud. Anyway, please provide the definition of these terms when first appears in the text, and consistently use the appropriate ones throughout the manuscript.
5. P. 2, L. 26: “PI JAXA…” This information should better be provided in Acknowledgements with more details, not in the main text.
6. P. 2, L. 29: Please provide the webpage with URL in a citation format.
7. P. 3, L. 16: Remove “(18)” after “Eighteen”.
8. P. 3, L. 16-17: Please spell out “LiDAR”.
9. P. 3, L. 16-17: “dataset” should be more specific, such as “DTM with a grid size of 2 m”.
10. P. 3, L. 24-17: “the 5m grid DTM… by the authors.” This portion seems unnecessary if the 5-m DEM by such aerial photogrammetry has never used for this study. Please clarify and remove this part if applicable.
11. P. 4, L. 31: Please consider to split the section here. The former subsection (3.1) can be about the existing knowledge on geological facts, while the latter (3.2) is about the updates of the existing geological maps using the authors' methods.
12. P. 5, L. 23: Change “There western” to “Their western”.
13. P. 6, L. 4-6: This portion should be in the subsection 3.1 (previous knowledge) as noted above.
14. P. 6, L. 7-9: This portion seems better to be stated in the Conclusions section as a future issue.
15. P. 6, L. 14: Better to use double quotations for “Super Master”. Also, please provide some additional explanations on this term (e.g., by just adding “as a reference”).
16. P. 6, L. 20: “The method identifies PS pixels (more than… 20133 exactly)” can be rephrased as “The method identifies 20133 PS pixels”.
17. P. 6, L. 23: To avoid misunderstandings for readers, it would be recommended to add some notes such as “Note that this LOS data is not projected onto the vertical component.” after “through time series.”
18. P. 7, L. 24: To avoid misunderstandings, “projected on” could be rephrased with “compared with”.
19. P. 7, L. 30: “, see the colour scale” can be removed.
20. P. 8, L. 25: This section is too long can be separated into “Discussion” and “Conclusions”. The lines after P. 10 L. 13 can be an independent section for “Concluding remarks”.
21. P. 10, L. 1-4: The vertical component of the tectonic activity is provided by the leveling data. However, the expression “locally confirmed by … LOS” is somewhat misunderstanding. It may be better to rephrase, such as “consistent with the LOS displacement” or else.
22. P. 10, L. 12: “So, in order to conclude,” can be removed.
23. Figure 1: As noted above, the extent for Figure 1b could be expanded to cover the entire data area for InSAR as well. In the caption, replace “Fig. 1a” with “(a)”, also for b and c.
24. Figure 3: Re-order the panels as:
a b
c d
e f
g h
Also, add scales and north directions for all the panels.
25. Figure 7: Please indicate in the caption that the western margin of the geological unit (flat land) is out of the UAS data and derived from the other data sources (coarser DEMs).
26. Figure 10: Use a citation format to represent the website and URL.

Dear authors,
thank you for revising the manuscript. Your paper is almost ready for publication, subject to some technical corrections.
Best regards,
yuichi hayakawa

* Please spell out DSM and DTM when they appear for the first time (DSM: P2 L24; DTM: P2 L15).
* The paper title shows UAS DTM, but now DSM is explicitly defined as the product of UAS in the manuscript. Please change the title and any other "UAS DTM” (in the body text and figure captions) to "UAS DSM" to be consistent throughout the manuscript.
* Please add access date and year to the citations to webpages.
https://www.natural-hazards-and-earth-system-sciences.net/Copernicus_Publications_Reference_Types.pdf