Application of Controlled-Source Audio-Frequency Magnetotellurics (CSAMT) for Subsurface Structural Characterization of Wadi Rum, Southwest Jordan

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper focuses on the application of the Controlled Source Audio-frequency Magnetotelluric (CSAMT) method to investigate the subsurface structural features of the Wadi Rum region in southwestern Jordan. The study aims to provide foundational data to support urban sustainability and geohazard assessment in the area. By employing resistivity mapping, the research reveals the key stratigraphic distribution and fault structures, offering critical insights for future urban planning and resource development. However, the paper can be further improved in terms of the comprehensiveness of the background analysis, the clarity of the data processing and methodological details, and the depth of the discussion on practical implications. Below are specific suggestions for improvement:

1. Consider specifying the study region and application context more explicitly, e.g., "Application of Controlled Source Audio-frequency Magnetotelluric Method for Urban Sustainability in Wadi Rum, Jordan", to better highlight the geographical and research focus.

2. Include specific results in the abstract, such as the measured resistivity ranges, primary stratigraphic features, and the study’s direct contributions to urban sustainability. This will enhance the clarity and attractiveness of the abstract.

3. Expand the discussion of CSAMT applications in similar geological settings by referencing successful case studies from other regions.

4. Highlight the unique geological characteristics of the Wadi Rum area and their relevance to urban planning and geohazard assessments, emphasizing the scientific value of this research.

5. In the “Data and Methods” section, provide a detailed explanation of the assumptions made during CSAMT data collection (e.g., homogeneous layers, signal propagation models). Discuss the validity and limitations of these assumptions in the context of the study area.

6. Include detailed descriptions of data quality control measures, such as noise processing techniques and criteria for data filtering.

7. Ensure consistency in the color schemes of figures and provide clear annotations (e.g., depth slices, total resistivity maps) to emphasize key findings such as fault lines and stratigraphic features. This will make the results more accessible to readers.

8. Deepen the discussion on the practical implications of the results, such as how they can inform infrastructure development, disaster risk reduction, or sustainable resource utilization.

9. Include a cost-benefit analysis of using the CSAMT method, emphasizing its advantages in terms of time and financial efficiency.

Comments on the Quality of English Language

The English need to be improved.

Author Response

Comment 1: Consider specifying the study region and application context more explicitly, e.g., "Application of Controlled Source Audio-frequency Magnetotelluric Method for Urban Sustainability in Wadi Rum, Jordan", to better highlight the geographical and research focus.

Response 1: Thank you for the suggestion. We already changed the title to "Application of Controlled Source Audio-frequency Magnetotelluric (CSAMT) for Subsurface Structural Characterization of Wadi Rum, Jordan"

Comment 2: Include specific results in the abstract, such as the measured resistivity ranges, primary stratigraphic features, and the study’s direct contributions to urban sustainability. This will enhance the clarity and attractiveness of the abstract.

Response 2: Thank you for pointing that out. We have already explained those resistivity ranges and associated lithologies in the abstract. 

Comment 3: Expand the discussion of CSAMT applications in similar geological settings by referencing successful case studies from other regions.

Response 3: Thank you for this good suggestion. However, the authors believe this is not necessary and only stick to the paper's case study. 

Comment 4: Highlight the unique geological characteristics of the Wadi Rum area and their relevance to urban planning and geohazard assessments, emphasizing the scientific value of this research.

Response 4: Thank you for pointing that out. We highlighted those characteristics in the Conclusion section (lines 380 - 387)

Comment 5: In the “Data and Methods” section, provide a detailed explanation of the assumptions made during CSAMT data collection (e.g., homogeneous layers, signal propagation models). Discuss the validity and limitations of these assumptions in the context of the study area.

Response 5: Thank you for the suggestion. We provided some details about the assumptions (lines 210 - 215).

Comment 6: Include detailed descriptions of data quality control measures, such as noise processing techniques and criteria for data filtering.

Response 6: Thank you for the suggestion. We haven't delved deep into data noise removal as the data is considered very good. 

Comment 7: Ensure consistency in the color schemes of figures and provide clear annotations (e.g., depth slices, total resistivity maps) to emphasize key findings such as fault lines and stratigraphic features. This will make the results more accessible to readers

Response 7: Thank you for pointing that out. We used different color schemes for different resistivity maps as those best describe the structures. Also, the fault lines are shown clearly in the total resistivity map. 

Comment 8: Deepen the discussion on the practical implications of the results, such as how they can inform infrastructure development, disaster risk reduction, or sustainable resource utilization.

Response 8: Thank you for the suggestion. The authors believe this is unnecessary and could be deviated away from the main aim of the paper.  

Comment 9: Include a cost-benefit analysis of using the CSAMT method, emphasizing its advantages in terms of time and financial efficiency.

Response 9: Thank you for mentioning that. We think this is not necessary because the tool is used by a private company and might affect their privacy policy. 

Reviewer 2 Report

Comments and Suggestions for Authors

In this paper, the subsurface structure characteristics in Wadi Rum, Southwest Jordan, were mapped using Controlled Source Audio-Frequency Magnetotellurics (CSAMT). Firstly, sounding curves for each station and the generated apparent resistivity maps at fixed depths were employed to identify zones of lower resistivity. Thereafter, the analysis of resistivity maps was integrated with prior geological information to indicate the subsurface features, including the presence of fault system development within the study area. As a result of this study, it was shown that the CSAMT approach provides reliable information and critical insights into the subsurface structure characterization of Wadi Rum, which is needed for the detailed assessment of potential geohazards and the strategic planning of future urban development within Southwest Jordan and other protected areas.

The need for this investigation is well described based on a review of the associated literature on the topic. The methodologies are well explained. The figures and tables presented in the manuscript are necessary. However, the structure of the manuscript seems not to be very good, and about 21 of the references are too old and should be updated. 

Comments to the authors:

1. Although the language of the manuscript is generally understandable, some improvements seem necessary.
2. I kindly recommend that the authors improve the quality of the figures, particularly pictures with small letters and numbers that are difficult to read.
3. I recommend that the title be changed to “Application of Controlled Source Audio-Frequency Magnetotellurics (CSAMT) for Subsurface Structural Mapping of Wadi Rum, Southwest Jordan.”
4. The introduction is too long. I recommend that the authors shorten it. Lines 53-109 should be moved to section 2 (Geological and Tectonic Setting) as sub-section 2.1 (Regional Geology), and lines 174-199 should be moved to sub-section 2.2 (Local Geology).
5. Lines 139-164 should be summarized and moved to section 3 “Methods and Data Collection” as sub-section 3.1 (General Overview of CSAMT).
6. Using the resistivity curve, show the geological profile of the litholayers in relation to the depth of sounding.
7. Limitations and Future Research: The article should make the potential for future research more specific.

Comments on the Quality of English Language

Although the language of the manuscript is generally understandable, some improvements seem necessary

Author Response

Comment 1: Although the language of the manuscript is generally understandable, some improvements seem necessary.

Response 1: Thank you for pointing this out. We made minor language improvements throughout the paper. 

Comment 2: I kindly recommend that the authors improve the quality of the figures, particularly pictures with small letters and numbers that are difficult to read.

Response 2: Thank you for the comment. We tried to make it bigger but the journal guidelines for figures won't allow us to enlarge figures. 

Comment 3: I recommend that the title be changed to “Application of Controlled Source Audio-Frequency Magnetotellurics (CSAMT) for Subsurface Structural Mapping of Wadi Rum, Southwest Jordan.”

Response 3: Thank you for the title recommendation. We have accordingly changed the title to what the reviewer suggested. 

Comment 4: The introduction is too long. I recommend that the authors shorten it. Lines 53-109 should be moved to section 2 (Geological and Tectonic Setting) as sub-section 2.1 (Regional Geology), and lines 174-199 should be moved to sub-section 2.2 (Local Geology).

Comment 5: Lines 139-164 should be summarized and moved to section 3 “Methods and Data Collection” as sub-section 3.1 (General Overview of CSAMT).

Responses 4 and 5: Thank you for the suggestions. However, the authors believe that the current structure fits well the paper comprehension framework to be easier for the reader to understand. 

Comment 6: Using the resistivity curve, show the geological profile of the litholayers in relation to the depth of sounding.

Response 6: Thank you for pointing that out. We believe this is not necessary at the current stage of the paper. 

Comment 7: Limitations and Future Research: The article should make the potential for future research more specific.

Response 7: Thank you for the suggestion. We believe this should be included in a second paper I the future. 

Reviewer 3 Report

Comments and Suggestions for Authors

I did not indicate grammar corrections, because English is not my first language. But I am able to say that the reading of the manuscript was easy and I did not have any problem for understanding the writing. However, the following comments should be addressed for the revision.

1、Some figures are not very clear, such as Figure 1, Figure 2, Figure 5, and Figure 6..

2、Suggest providing a topographic map of the study area with contour lines in Figure 1.

3、The CSAMT survey was done very well, but the author did not explain the faults in the area. The author also did not provide geological interpretation of the resistivity inversion results, such as which geological layer the results reflect? It only described the distribution of resistivity.

Author Response

Thank you for your very informative comments and feedback. We highly appreciate such feedback. 

Comment 1: Some figures are not very clear, such as Figure 1, Figure 2, Figure 5, and Figure 6.

Response 1: Thank you for pointing this out. We enlarged some of those figures to fit within the regulations of the journal. 

Comment 2: Suggest providing a topographic map of the study area with contour lines in Figure 1.

Response 2: Thank you for the suggestion. Actually, the topographic map is included in Figure 1 (inset map) as we believe it is unnecessary to have a separate figure for topo map. 

Comment 3: The CSAMT survey was done very well, but the author did not explain the faults in the area. The author also did not provide geological interpretation of the resistivity inversion results, such as which geological layer the results reflect? It only described the distribution of resistivity.

Response 3: Thank you for pointing that out. We agree with your comment, but the distribution of the resistivity was associated with the faults and lineaments more into the regional scale which indeed led to the formation of the giant graben structure in the area. 

Reviewer 4 Report

Comments and Suggestions for Authors

The study applies the Controlled Source Audio-Frequency Magnetotelluric (CSAMT) method to map subsurface structures in Wadi Rum, southwest Jordan. A graben structure with NE-SW trending faults indicates central subsidence and uplifted edges. The study highlights tectonic activity and sedimentary deposition, with implications for urban planning and hazard mitigation. While CSAMT proves effective, the study acknowledges the need for additional geophysical methods, error analysis, and borehole validation to enhance the accuracy and robustness of interpretations. please find the following comments

1.      The study lacks borehole data or other direct geological information to validate the CSAMT-derived resistivity profiles. How were these interpretations cross-checked?

2.      There is insufficient discussion about the uncertainties in resistivity measurements, especially at deeper layers where attenuation could impact accuracy. Can the authors provide a quantitative uncertainty analysis?

3.      The study relies solely on CSAMT. Why were other geophysical methods, such as seismic reflection or magnetic surveys, not integrated to corroborate the results?

4.      The identified graben structure and faults suggest significant tectonic activity. How do the findings align with previous tectonic models of the Wadi Rum region?

5.      The limitations of frequency-dependent depth penetration are acknowledged. How were the resistivity values at deeper layers adjusted for potential signal attenuation?

6.      The study does not compare its findings with similar geophysical surveys in other tectonically active regions. Can the authors contextualize their results within the broader literature?

7.      How did lateral variations in resistivity affect the overall resolution, and what steps were taken to minimize these effects?

8.      The 3D model is valuable but limited in detail. Can the authors provide more detailed cross-sectional interpretations of key fault zones?

9.      How was noise interference mitigated during the CSAMT survey, particularly in the low-resistivity layers?

10.  Were specific criteria used to select the frequencies for depth slicing, and how do they impact the resolution?

11.  The second layer is identified as medium-grained sandstone. Could it be possible to distinguish between different sandstone formations using CSAMT alone?

12.  What criteria were used to identify the NE-SW trending faults, and how confident are the authors in their lateral and vertical extents?

13.  Do the authors plan to integrate direct geological data or alternative geophysical methods in future studies to validate and enhance the interpretations?

14.  How can the findings be translated into practical guidelines for urban planning and hazard mitigation in the Wadi Rum area?

Comments on the Quality of English Language

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

Author Response

Thank you for your invaluable comments and feedback. I have to say these are some of the most informative comments directed at the topic of the paper we have received. We greatly appreciate those comments. 

Comment 1: The study lacks borehole data or other direct geological information to validate the CSAMT-derived resistivity profiles. How were these interpretations cross-checked?

Response 1: Thank you for pointing that out. Indeed, this CSAMT study was done qualitatively with the absence of borehole data and we pointed that out in the paper. The main goal is to test the ability of the CSAMT to map the resistivity distribution and content it to the geological information we have from prior resources. 

Comment 2: There is insufficient discussion about the uncertainties in resistivity measurements, especially at deeper layers where attenuation could impact accuracy. Can the authors provide a quantitative uncertainty analysis?

Response 2: Thank you for pointing this out. We agree that there are some uncertainties which is the main issue in all geophysical methods, but this paper discussed the qualitative approach of the CSAMT and the quantitative approach would be another project for a second paper. 

Comment 3: The study relies solely on CSAMT. Why were other geophysical methods, such as seismic reflection or magnetic surveys, not integrated to corroborate the results?

Response 3: Thank you for mentioning this. Unfortunately, there are no local-scale geophysical methods done in the area. There are big regional-scale surveys (thousands of km) done like magnetic surveys, which are explained briefly in Figure 2. 

Comment 4: The identified graben structure and faults suggest significant tectonic activity. How do the findings align with previous tectonic models of the Wadi Rum region?

Response 4: Thank you for pointing this out. We explained the relation between the fault structures and the prior geological and large-scale tectonic information (previous studies) in the region although the Wadi Rum region lacks local-scale tectonic models.  

Comment 5: The limitations of frequency-dependent depth penetration are acknowledged. How were the resistivity values at deeper layers adjusted for potential signal attenuation?

Response 5: Thank you for clarifying that. We explained such an attenuation technique through the skin-depth attenuation equation (line 281)

Comment 6: The study does not compare its findings with similar geophysical surveys in other tectonically active regions. Can the authors contextualize their results within the broader literature?

Response 6: Thank you for mentioning this point. We believe that the Gulf of Aqaba is unique and different in terms of its tectonic structure and geological framework, hence we couldn't directly articulate the use of geophysical methods to other tectonic regions. Perhaps this could be discussed in future work in the area. 

 Comment 7: How did lateral variations in resistivity affect the overall resolution, and what steps were taken to minimize these effects?

Response 7: Thank you for pointing that out. However, we used the 1-D inversion results from the sounding curves of Resistivity vs Frequency and Phase vs Frequency to obtain a broader distribution of resistivity. 

Comment 8: The 3D model is valuable but limited in detail. Can the authors provide more detailed cross-sectional interpretations of key fault zones?

Response 8: Thank you for the suggestion. We explained the key fault zones in the total resistivity map. Also, we believe the 3D model from resistivity profiling provides enough information for the reader to understand the fault structures from the previous total resistivity map.

Comment 9: How was noise interference mitigated during the CSAMT survey, particularly in the low-resistivity layers?

Response 9: Thank you for your question. To mitigate the noise, we increased the spacing between receiving electrodes to amplify the electric field strength, and also utilized high-current transmission to strengthen the effective signal.

Comment 10: Were specific criteria used to select the frequencies for depth slicing, and how do they impact the resolution?

Response 10: Thank you for mentioning this point. In fact, the selected frequencies help create a better visualization of the contrast in the resistivity profiles representing shallower and deeper structures. The measured electrical properties of the subsurface layers notably transitioned from lower resistivity zones to medium, and from medium to higher resistivity as depth increases.

Comment 11: The second layer is identified as medium-grained sandstone. Could it be possible to distinguish between different sandstone formations using CSAMT alone?

Response 11: Thank you for pointing this out. Using CSAMT alone might not give a detailed explanation of the lithologies, but the integration of geological, tectonic, and geophysical (CSAMT) data is a powerful approach that we adopted for better subsurface characterization.

Comment 12: What criteria were used to identify the NE-SW trending faults, and how confident are the authors in their lateral and vertical extents?

Response 12: Thank you for your question. The two faults are already discussed in the area's geological map. From CSAMT data, it is clearly shown that at shallow depths (high frequencies), the area is mainly dominated by sediments with relatively low resistivity values. In addition to its large thickness, the penetration of these layers is small which can be inferred that this area is exposed to subsidence allowing the sediments to accumulate in large amounts there. Also, the total resistivity map shows the resistivity contrast from the CSAMT stations, and the two suspected faults run in the directions of northeast (NE) and southwest (SW).

Comment 13: Do the authors plan to integrate direct geological data or alternative geophysical methods in future studies to validate and enhance the interpretations?

Response 13: Thank you for pointing this out. Indeed, we are trying to obtain some borehole data from authorities near the study area. Also, there is a possible research project that could involve using the new advanced towed-Transient Electromagnetic (tTEM) instrument from Aarhus University in Denmark.

Comment 14: How can the findings be translated into practical guidelines for urban planning and hazard mitigation in the Wadi Rum area?

Response 14: Thank you for mentioning this point. The authors believe that the findings of this paper contributed to the identification of faults and structural features through CSAMT surveys. This provides critical information to decision-makers, aiding in the selection of areas for future hazard assessment and urban developmental planning. 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The research content of the entire paper is innovative, and the data and methods used are rigorous. The qualitative interpretation of CSAMT data has been proven to be an effective tool for mapping structural features, despite the lack of direct geological information about the study area.

Comments on the Quality of English Language

The English proficiency of this article is generally good, with clear and coherent sentence structures.. However, there are occasional issues with word choice and phrasing that could be polished for smoother readability and greater academic precision

Author Response

Comment 1: The research content of the entire paper is innovative, and the data and methods used are rigorous. The qualitative interpretation of CSAMT data has been proven to be an effective tool for mapping structural features, despite the lack of direct geological information about the study area.

Response 1: Thank you for your kind comment. We agree that the SAMT method has been qualitatively effective for mapping structural features.  

Reviewer 3 Report

Comments and Suggestions for Authors

Although the author has made revisions to the manuscript, it is still not comprehensive enough. The following comments should be addressed for the revision.

It's still a matter of fault interpretation. For example, in Figure 7, the dashed lines represent two north-south faults, but it cannot be seen from Figure 7 that these two faults are related to the distribution of electrical resistivity. This should be explained in detail.

In addition, this article mainly focuses on qualitative explanations, which leads to insufficient research depth. The author should invert the resistivity data and then interpret faults, strata, etc.

Author Response

Comment 1: It's still a matter of fault interpretation. For example, in Figure 7, the dashed lines represent two north-south faults, but it cannot be seen from Figure 7 that these two faults are related to the distribution of electrical resistivity. This should be explained in detail. 

Response 1: Thank you for your comment. Figure 7 visualization is related to Figure 6 which shows the different distribution values of resistivity as we go deeper, as well as the geological map in Figure 3. The Electrical Resistivity Contrast (sediments/basement rocks) here is associated with faults and fractures. CSAMT data can differentiate between these zones based on resistivity contrasts. This is governed by the two faults that run northeast (NE) and southwest (SW), not only north-south direction. We modified the manuscript by adding some details from previous studies in yellow in the revised manuscript. 

Comment 2: In addition, this article mainly focuses on qualitative explanations, which leads to insufficient research depth. The author should invert the resistivity data and then interpret faults, strata, etc.

Response 2: Thank you for the comment. We inverted the CSAMT data from the 1D VES-sounding curves and interpreted it qualitatively to test the ability of CSAMT method for qualitative results, which is the main scope of this article. Indeed, the full quantitative invesion might be needed in the future for other research work

Reviewer 4 Report

Comments and Suggestions for Authors

Thank you for your detailed and thoughtful responses to my comments. Your clarifications have provided valuable insight into the scope, limitations, and methodologies of your study. Below, I give a few additional reflections and suggestions based on your replies.

1. While I understand that the study aimed to qualitatively test CSAMT capabilities in mapping resistivity distributions, the lack of borehole data remains a significant limitation.
2. I recognize that uncertainty quantification is outside the scope of this qualitative study. However, even a qualitative discussion on potential errors and their implications in the interpretation would strengthen the paper. If possible, a brief mention of how future studies might approach a quantitative uncertainty assessment could be beneficial.
3. Your explanation regarding the absence of local-scale geophysical surveys is understandable. However, given the availability of large-scale magnetic surveys, a discussion on how those regional findings correlate with your CSAMT results might enhance the study’s impact.
4. Your reasoning for not directly comparing with other tectonic regions is noted. However, even a brief mention of how CSAMT has been used in other similar settings, with any key differences highlighted, would provide helpful context for readers.
5. 1D inversion from resistivity versus frequency and phase versus frequency data is a good approach. If possible, a discussion of its limitations in capturing lateral variations would be beneficial.
6. Your response highlights the importance of selected frequencies in resolving subsurface features. Clarifying how frequency choices influence resolution at various depths will be useful for readers unfamiliar with the method.
7. I appreciate your response regarding CSAMT's limitations in distinguishing between different sandstone formations. If available, referencing prior studies that have attempted this distinction using geophysics could provide additional depth to your discussion.

Comments on the Quality of English Language

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

Author Response

Comment 1: While I understand that the study aimed to qualitatively test CSAMT capabilities in mapping resistivity distributions, the lack of borehole data remains a significant limitation.

Response 1: Thank you for the comment. Indeed, the absence of direct borehole data is one of the main challenges in the area.

Comment 2: I recognize that uncertainty quantification is outside the scope of this qualitative study. However, even a qualitative discussion on potential errors and their implications in the interpretation would strengthen the paper. If possible, a brief mention of how future studies might approach a quantitative uncertainty assessment could be beneficial.

Comment 3: Your explanation regarding the absence of local-scale geophysical surveys is understandable. However, given the availability of large-scale magnetic surveys, a discussion on how those regional findings correlate with your CSAMT results might enhance the study’s impact.

Responses 2 and 3: Thank you for the comment. Indeed, a quantitative assessment of subsurface uncertainty by using inverted 2D and 3D resistivity maps as well as drilling borehole data (new data) would be very beneficial for a full structural assessment in the area. We added some information to the manuscript and highlighted this explanation in yellow in the conclusion section (lines 409- 411).

Comment 4: Your reasoning for not directly comparing with other tectonic regions is noted. However, even a brief mention of how CSAMT has been used in other similar settings, with any key differences highlighted, would provide helpful context for readers.

Response 4: Thank you for your nice suggestion. We added some similar case studies highlighted in yellow (lines 143-146) per your suggestions. 

Comment 5: 1D inversion from resistivity versus frequency and phase versus frequency data is a good approach. If possible, a discussion of its limitations in capturing lateral variations would be beneficial. 

Response 5: Thank you for your comment. 1D inversion from resistivity versus frequency and phase versus frequency is a common step toward resistivity vs depth inversion maps. We feel that such discussion is not necessary here.

Comment 6: Your response highlights the importance of selected frequencies in resolving subsurface features. Clarifying how frequency choices influence resolution at various depths will be useful for readers unfamiliar with the method.

Response 6: Thank you for your comment. The selected frequencies help create a better visualization of the contrast in the resistivity profiles representing shallower and deeper structures. The measured electrical properties of the subsurface layers notably transitioned from lower resistivity zones to medium, and from medium to higher resistivity as depth increases. We highlighted this comment in (lines 341-343).

Comment 7: I appreciate your response regarding CSAMT's limitations in distinguishing between different sandstone formations. If available, referencing prior studies that have attempted this distinction using geophysics could provide additional depth to your discussion.

Response 7: Thank you for your comment. Unfortunately, we couldn't find similar studies available in the meantime. 

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

No modifications or explanations were found by the author regarding the fault interpretation and the inversion mentioned last time.

Author Response

Comment 1: No modifications or explanations were found by the author regarding the fault interpretation and the inversion mentioned last time.

Resounse1: Thank you for pointing that out. Regarding the inversion method, we used equation (1) (line 269) to obtain resistivity information from the electrical field and magnetic field; and used equation (2) (line 287). We highlighted that in the revised manuscript. Regarding fault interpretation, we have already added some details (lines 361- 366) with similar case studies.