Ground Penetrating Radar of Neotectonic Folds and Faults in South-Central Australia: Evolution of the Shallow Geophysical Structure of Fault-Propagation Folds with Increasing Strain
Round 1
Reviewer 1 Report
This research uses GPR to study inner structure of reverse fault systems and demonstrates various expression of the fault and fold deformation on the GPR images. The manuscript is well, but reviewer advices to do it shorter and leave only the most demonstrational pictures. It is better to show primary and interpreted radargrams together that reader could more trust author’s data. Other notes below:
Notes:
1. Some lettering in figures is too small (see, for example fig. 1-2) So it needs to be correct.
2. The word “reverse” is extra in line 35: “The surface manifestations of reverse faulting can vary significantly…” as further authors say about fault kinematics in the brackets.
3. Lines 89-90: Authors write: «Ground penetrating radar (GPR) is commonly used to investigate neotectonic faults in seismically active regions (e.g., [5], [23], [24])”. But there are already huge quantity of articles devoted to surface ruptures associated with earthquakes so it would be nice if authors to mention some of them to show that they known recent literatures.
4. Organizing of figures 1 and 2 is not comfortable for reader. Figure 3 repeats figure 1e.
5. Check caption in figure 4. Where is a black line in the GPR profiles?
6. In conclusion, authors twice say trivial outcomes about benefit of GPR but the fact is well-known and the world uses it in many researches. Therefore, I advise to single out the main things from this long and detail study and listed as 1, 2, 3…
As a whole after all, it is worth research to be publish.
Author Response
REVIEW 1
0) This research uses GPR to study inner structure of reverse fault systems and demonstrates various expression of the fault and fold deformation on the GPR images. The manuscript is well, but reviewer advices to do it shorter and leave only the most demonstrational pictures.
>> We thank the reviewer for their constructive review of our manuscript. Some effort has been made to tighten the manuscript however the strength of this paper is in its documentation of diverse geophysical expressions of near-fault structure and to do this properly we need to provide sufficient detail in the text.
It is better to show primary and interpreted radargrams together that reader could more trust author’s data.
>> We added figures of the uninterpreted transects in the supplementary material to increase this transparency without lengthening the manuscript.
1) Some lettering in figures is too small (see, for example fig. 1-2) So it needs to be correct.
>> Font and detail sizes were adjusted.
2) The word “reverse” is extra in line 35: “The surface manifestations of reverse faulting can vary significantly…” as further authors say about fault kinematics in the brackets.
>> Removed “reverse” from the text.
3) Lines 89-90: Authors write: «Ground penetrating radar (GPR) is commonly used to investigate neotectonic faults in seismically active regions (e.g., [5], [23], [24])”. But there are already huge quantity of articles devoted to surface ruptures associated with earthquakes so it would be nice if authors to mention some of them to show that they known recent literatures.
>> References are provided in brackets a the end of line 90. The cited references are appropriate and adding general references for surface ruptures is considered subjective in its value, as there is a huge volume of known research on this already and the objective of adding additional references here is unclear.
4) Organizing of figures 1 and 2 is not comfortable for reader.
>> It is unclear what is meant by this comment but we have reviewed these figures and find them appropriately organized and clear.
Figure 3 repeats figure 1e.
>> The purpose of Fig. 1e is to emphasize the locations of GPR transects on the property and in relation to faulting related features that are visible to the naked eye without the distraction by interpreted features. Adding all line work in the same Figure creates a very unclear figure and we consider it clearer to separate them.
5) Check caption in figure 4. Where is a black line in the GPR profiles?
>> We adjusted the figure caption.
6) In conclusion, authors twice say trivial outcomes about benefit of GPR but the fact is well-known and the world uses it in many researches. Therefore, I advise to single out the main things from this long and detail study and listed as 1, 2, 3…
>> Thank you for this constructive comment. We have completely rewritten the Conclusions section of the paper. We have shortened it and focus it on the key findings. It is much improved.
Reviewer 2 Report
1) The feild photos (ex Figure 4) are not so qualified in the generated pdf, and can't support well the GPR data!
2) although the presented MS is intresting but still could be improved by more feild data as well as even other geophysical surveing like as IP/RS in some part.
3) i think authors also confirm me that the MS in presented form, without any more comparation with parallel controller such as feild data or by using other indirect observing methods, some of done interpretation could be failed!
Author Response
REVIEW 2
1) The feild photos (ex Figure 4) are not so qualified in the generated pdf, and can't support well the GPR data!
>> Higher-quality figures are now embedded in the manuscript.
2) although the presented MS is intresting but still could be improved by more feild data as well as even other geophysical surveing like as IP/RS in some part.
>> The study area is located in a very remote region where geophysical surveys are difficult to conduct, both, in regards to execution and financial expense. There are ongoing studies by others in this region but this is beyond the scope of our paper.
3) i think authors also confirm me that the MS in presented form, without any more comparation with parallel controller such as feild data or by using other indirect observing methods, some of done interpretation could be failed!
>> All of the sites studied herein have been compared with field observations. The Willunga Fault, for example, was trenched in several locations and has been field mapped – we made an extensive effort to compare GPR with field data. All of the other locations were mapped in the field, but the critical point is that these are broad scarps with no discrete surface ruptures, so there is little to see there beyond the broad scarp. This necessitated the use of GPR. The research methodology is sound.
Reviewer 3 Report
The study is well performed. The manuscript is fluent, I had a good time reading it. Data are well presented although the figures need some work to be made a little more readable.
My opinion about this manuscript is generally positive even though some points need to be further discussed and some improved or corrected. I hope my suggestions (comments attached with the reviewed pdf) will be useful to improve this work. I consider the manuscript acceptable for publication with moderate revision.
Comments for author File: 
Comments.pdf
Author Response
REVIEW 3
1) Line 35 – 36: If the manifestations of the superface faulting depend on the kinematics (which is correct) then at the beginning of the sentence it is necessary to remove "reverse", so as to include all the kinematics.
I suggest rephrasing with: "The manifestations of surface faulting can vary significantly, depending on the characteristics of faulting (e.g., fault kinematics, geometry, slip) ".
>> adjusted as suggested
2) I also suggest adding some references of works that study the coseismic surface faulting so as to give immediate broad interest to the paper. They can be Fletcher et al. (2014), Brozzetti et al. (2019) and Bello et al. (2021), from different areas of the world.
Ref.
Brozzetti, F., Boncio, P., Cirillo, D., Ferrarini, F., de Nardis, R., Testa, A., et al. (2019). High ‐ resolution field mapping and analysis of the August – October 2016 coseismic surface faulting (central Italy earthquakes): Slip distribution, parameterization, and comparison with global earthquakes. Tectonics, 38. https://doi.org/10.1029/2018TC005305
Fletcher J. M., Teran O. J., Rockwell T. K. et al., “Assembly of a large earthquake from a complex fault system: surface rupture kinematics of the 4 April 2010 El Mayor – Cucapah (Mexico) Mw 7.2 earthquake, ”Geosphere, vol. 10, no. 4, pp. 797–827, 2014. https://doi.org/10.1130/GES00933.1
Bello S., Scott C. P., Ferrarini F., Brozzetti F., Scott T., Cirillo D., de Nardis R., Arrowsmith J. R., Lavecchia G.. "High-resolution surface faulting from the 1983 Idaho Lost River fault Mw 6.9 earthquake and previous events". Scientific Data, 2021, vol. 8 1 pg. 68 https://doi.org/10.1038/s41597-021-00838-6
>> We cited the suggested references in the text and added them in the reference list.
3) The authors started the manuscript in a great way and touching on interesting topics. I suggest keeping the first part of the introduction general, talking about the surface faulting without going into the detail of the kinematics.
For example, the topic of distributed deformation has become of great interest in recent years and could give power to the reading of the first part of the article (Ferrario and Livio, 2018, 2020; Oskin et al., 2012; Zinke et al., 2014 ; Bello et al., 2022).
Then we focus on the study area and therefore on its details.
>> We cited the suggested references in the text and added them in the reference list. The text is adjusted as follows: “[…] E.g., geophysical and field observations of cumulative slip indicate that up to two thirds of strain on thrust faults may be accommodated by distributed folding [7], [8]. The same can be seen at the scale of individual earthquakes; the Chi-Chi [9] El Asnam (e.g., [10], [11]) and Peterman Ranges earthquakes, for instance, all displayed distributed deformation at scales of 10 to >1000 times the vertical displacement. The presence of strong horizontal layering, material property contrasts and less cohesive near-surface materials may encourage distributed deformation that is greatly in excess of the displacement localized at the principal slip zone (e.g., [12], [13], [14], [15], [16])[…]”.
4) Figure 1: The texts are very small and difficult to read.
>> Font and detail sizes were adjusted.
5) Better close the introduction with the sentence "We aim .... progressive strain". Do not anticipate conclusions here.
Rather, add a sentence about why this study is important, trying to engage the potential reader in the continuation of the reading.
>> Adjusted as follows: “[…] We aim to diagnose neotectonic structural and sedimentological features in the GPR that provide insights into the evolution of near surface features with progressive strain. This can provide implications for the associated distributed deformation and, by extension, the fault displacement hazard in the affected area […].”
6) Although the photogrammetry methodology is now in common use, listing the steps and describing the characteristics of the method used, as well as the characteristics of the products obtained cannot be omitted. One solution to not lengthen the text if this is not a fundamental part of the work, is to cite the earliest and most recent works that have used these methodologies (e.g., Westoby et al., 2012; Johnson et al., 2014; Crosby et al., 2020; Cirillo et al., 2022).
Ref.
Westoby M. J., Brasington J., Glasser N. F., Hambrey M. J., Reynolds J. M., “'Structure-from-Motion' photogrammetry: A low-cost, effective tool for geoscience applications,” Geomorphology, vol. 179, pp. 300-314, 2012. https://doi.org/10.1016/j.geomorph.2012.08.021
Johnson K., Nissen E., Saripalli S., Arrowsmith J. R., McGarey P., Scharer K., Williams P., Blisniuk K. “Rapid mapping of ultrafine fault zone topography with structure from motion" Geosphere, vol. 10, no. 5, pp. 969–986, 2014. https://doi.org/10.1130/GES01017.1
Crosby C. J., Arrowsmith J R., Nandigam V., “Zero to a trillion: Advancing Earth surface process studies with open access to high-resolution topography,” Developments in Earth Surface Processes, vol. 23, pp. 317–338, 2020. https://doi.org/10.1016/B978-0-444-64177-9.00011-4
Cirillo, D., Cerritelli, F., Agostini, S., Bello, S., Lavecchia, G., Brozzetti, F. "Integrating Post-Processing Kinematic (PPK)–Structure-from-Motion (SfM) with Unmanned Aerial Vehicle (UAV) Photogrammetry and Digital Field Mapping for Structural Geological Analysis." ISPRS Int. J. Geo-Inf. 2022, 11, 437. https://doi.org/10.3390/ijgi11080437
>> We cited the suggested references in the text and added them in the reference list.
7) Lines 157-160, All these complications, together or separately, are widespread all over the world (with the exception of wombats, which are however replaced by coyotes, foxes, badgers, etc.). Just mention them as general complications.
>> Adjusted as follows: “[…] Additional factors that can influence GPR signals include extent and mineralogy of the weathered zone, low slip rates, climatic conditions that allow deep weathering of colluvial deposits, and an abundance of burrowing mammals such as rabbits and wombats[…].”
7) Line 187: Refer to figure
>> Adjusted
8) Figure 3: white roman numbers are difficult to see. Please, enlarge them.
>> adjusted.
9) Line 249: Despite the use of both terms, it is now commonly accepted to write them in the following way: "hanging wall" and "footwall". Uniform throughout the text.
>> adjusted.
10) The value of this figure cannot be appreciated as it is too condensed. As it is arranged, it is not possible to enlarge it further. I thinkit is a very important figure for this work, and therefore deserves to be clearly legible. I suggest separating the three panels into three distinct figures.
>> This figure was intended to be a full A4 page but following the provided Journal template we were not sure if that was accepted.
Enlarged and rotated figure so that is as big as possible.
11) Lines 324 – 330: What can these other features be? Specify it with examples: e.g., ...
>> “other features” refer to other definite, probable or possible surface traces.
Adjusted as follow: “[…] with other identified definite, probable, or possible surface features […].”
12) Figure 6: Please, put a loc map on h showing the area of g
>> adjusted
13) Please, as a general comment, I ask the authors to make the figures full page whenever possible to improve readability. Figures are the most important part of the work. While this should be the case, not all readers will read every part of your article. They will read a part of it, and then they will concentrate a lot on the figures. It is frustrating for the reader to only be able to glimpse the texts and the things the authors want to show.
>> All interpreted GPR transect figures are intended to be the full width of an A4 page but following the provided Journal template we were not sure if that was accepted.
Enlarged figures where possible.
14) The manuscript is extremely detailed and it was enjoyable to read. In these conclusions, however, I would expect to see, as well as a very brief summary in the form of, for example, a bulleted list of the main findings, of the general implications for your study. What does your study have a particular impact on? What are the implications for the study area? What are the general implications, what makes this study worth reading and interesting for an American or European geoscientist who is not involved in studying the Austrialian area?
Responding briefly to these points, which could also be minimally included in the abstract and intro, would make this work, already well done, more interesting.
>>We thank the reviewer for this comment and we agree that some more general implications would benefit the article. To this end, we revised the Conclusions extensively and focused on more high-level conclusions that would appeal to a broader audience.
Round 2
Reviewer 2 Report
Thanks for the answer to the proposed question (below N3) about the possibility of parallel comparison methods, which it is convincing enough for now!
However, care must still be taken with the sensitivity or weakness of GPR in clay materials!
Thus, to avoid any misunderstanding between secondary surficial scarps and active/seismogenic fault scarps in the active tectonic domain in order to have more robust and accurate data, we suggest to combine different geophysical methods together (not only GPR) in addition to field surveys.
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3) ...... more comparation with parallel controller such as feild data or by using other indirect observing methods....
>> All of the sites studied herein have been compared with field observations. The Willunga Fault, for example, was trenched in several locations and has been field mapped – we made an extensive effort to compare GPR with field data. All of the other locations were mapped in the field, but the critical point is that these are broad scarps with no discrete surface ruptures, so there is little to see there beyond the broad scarp. This necessitated the use of GPR. The research methodology is sound.
