Reply of the authors of

Popigai and Chicxulub craters: multiple impacts and their associated grabens

RC1: 'Comment on egusphere-2024-866', Anonymous Referee #1, 28 May 2024.

Thank you for the detailed review. We are ready to account your critical comments and if possible further comments based on other suggestions. We can make deep changes in the manuscript. We are not experts on the impact craters; these results are only one example of our applications of the gravity aspects to test various features on the Earth, the Moon, and Mars (see references in our manuscript). It is well possible that we missed some important references from really a great amount of them, so we would be happy if you are more specific in your review and would recommend what is missing and should be newly mentioned.

The manuscript could be significantly changed if we get a chance to publish it.

• We guarantee our computations of the gravity aspects, but we cannot be sure about our new interpretations. You are expert, we cannot compete.

• You wrote: …a fatal flaw of not constraining their results with other available data that would allow for additional constraints and in this case refute their ideas of multiple impacts in the region of either of these craters.  Based on the seismic profiles, you conclude (a majority opinion) that the gravity low NE of Chicxulub or the southern tail are pre-impact structures. It looks like we did not explain well our results, namely those following from the strike angles. In a big contrast to the gravity anomalies, showing simply a gravity low for NE of Chicxulub or the tail, the strike angles react with a halo as for any other impact crater, not an arbitrary circular-like gravity low.

     We know majority opinion that the gravity low NE of the main Chicxulub crater and the southern anomaly (the tail) are pre-impact structures. It would be naive to base our hypothesis that there is more than one crater only on gravity anomalies. But also the strike angles behave as expected for the impact crater (see above and Figs. 2b–e).

• We do not work only with the gravity anomalies but with the gravity aspects, a set of functions of the disturbing gravitational field potential. May we recommend the reader to read the theory of the gravity aspects in Klokočník al (2017) and (2020) or in Supplement S1 (which was submitted to SE EGU Discussion together with the main text)? The difference between the gravity anomalies and the gravity aspects is like the difference between a bicycle and a Cadillac.

• Although we now drive a Cadillac and not a bicycle, we are aware that the gravity data alone cannot solve the inverse task in a unique way. We always need additional data. It is emphasized in our text.

We agree with the following critics and would change our text accordingly:

…Additionally, the discussions of both craters is a strange combination of specific details that are not really important to their regional story and missing other papers and data that could test their proposed ideas…  

We need, however, a more specific review. We would be happy for recommendations of missing papers, not only for a general, critical remarks like … in both the case of Popagai and Chicxulub the authors have not used their new data to examine exciting details of impact structure and processes where we know there are impacts to study and instead have gone down the proverbial rabbit hole to chase circular gravity lows arguing for impacts where the geologic data in both locations do not show any evidence.

Would it be possible to take our hypothesis about Chicxulub and Popigai as a working hypothesis, a minority opinion, and test it with a new look? If you assume that a crater is a double/multiple crater, you probably will conduct your research in another way/style than if you stick to the traditional, majority view. We know that against an impact origin of Chicxulub II speak the seismic profiles. But we found only 1-2 such profiles NE of the main Chicxulub crater roughly in the direction where we predict the second crater (the profiles from e.g. Gullick et al 2008, 2016). We do not know about any seismic profile crossing the southern tail. In a big contrast to this, the network of seismic profiles crossing the main Chicxulub crater is dense. For the case of Popigai, we did not find any seismic profile at all. The magnetic field over the Popigai region is based (probably till now) on data from a 2.5 km grid compilation of the former Soviet Union.

Kind regards: the authors.

Status: this preprint is open for discussion.

Popigai and Chicxulub craters: multiple impacts and their associated grabens

Jaroslav Klokocnik, Vaclav Cilek, Jan Kostelecky, and Ales Bezdek

Status: open (until 21 Jun 2024)                                                                                                         RC1: 'Comment on egusphere-2024-866', Anonymous Referee #1, 28 May 2024.

I was excited to read a paper discussing both Popagai and Chicxulub given these are two of the largest preserved impact basins on Earth.  The authors are experts in gravity methods and do a very nice job laying out the efforts to provide update gravity anomaly maps for each of the two impact structures.   However, the inferences the authors go on to make about both structures include a fatal flaw of not constraining their results with other available data that would allow for additional constraints and in this case refute their ideas of multiple impacts in the region of either of these craters.  Additionally the discussions of both craters is a strange combination of specific details that are not really important to their regional story and missing other papers and data that could test their proposed ideas.  For instance at Popagai the whole discussion about diamonds as a shock indicator is unneeded and instead a discussion of the structural geology, erosion depth, drilling results, etc should have been included to allow for aspects like interrogating the new gravity map for what it represents in terms of Popagai's structure.  You should a very interesting low gravity ring that could represent the annualar trough for instance or could represent a highly shocked peak ring (an exciting possibility!)...yet instead of diving into such intriguing results, the authors focus on other features in the region that can be explained tectonically and do not have any evidence of an impact origin.  For Chicxulub, the authors similarly focus on a detail that is not resolvable in their gravity map (the Holocene aged karst feature the ring of cenotes, which exist due to caves formed within the inner ring of the crater), but then do not detail the ways in which their new gravity map differs from previous ones that might be illustrative of the crater heterogeneities. For instance its a cool opportunity to consider the relative contributions from impact trajectory versus target heterogeneity.  Instead they suggest the pre-existing sedimentary basin to the NE of the crater might be a second impact despite seismic images across this feature which show no structure evidence for any kind of impact (no rim faults, terrace zone, central uplift, etc- see the papers already referenced for plenty of evidence its not an impact).   Just because it is a gravity low does not mean it's an impact...it usually just means it's a sedimentary basin.  Moreover the authors then try to attribute the pre-existing rift that lies south of the crater and likely continued through the area the impact formed as somehow caused by the impact.  This structure has been drilled and imaged on seismic data is a known tectonic graben of Jurassic to Cretaceous age, not made by the Cretaceous-Paleogene impact.  In effect the features being highlighted adjacent to Chicxulub are well studied in other papers and do not correlated in age and have data specifically demonstrating these are not of impact origin.  Thus in both the case of Popagai and Chicxulub the authors have not used their new data to examine exciting details of impact structure and processes where we know there are impacts to study and instead have gone down the proverbial rabbit hole to chase circular gravity lows arguing for impacts where the geologic data in both locations do not show any evidence.  I suggest to reject this paper as it stands and recommend to the authors to rebuild their paper using these gravity anomaly maps to improve our knowledge of Chicxulub and Popagai instead.

Thank you for your support. There are two important factors in the gravity field investigation: better data and a better method. Data: the EIGEN 6C4 gravity model with the GOCE gradiometry data represents improvement over its predecessor EGM2008 by about one order in the ground resolution and precision, namely for the polar areas. Method: the gravity aspects describe the density anomalies (causative bodies) more completely than only the gravity anomalies can do. Combined together, with the improved data and the method, we can come with new results (namely with the combed gravity strike angles). They require a revision of existing interpretations. This is exactly what we do.

Rebuttal letter. Reply of the authors to the second review to:

Popigai and Chicxulub craters: multiple impacts and their associated grabens

Jaroslav Klokocnik, Vaclav Cilek, Jan Kostelecky, and Ales Bezdek

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor |

• RC1: 'Comment on egusphere-2024-866', Anonymous Referee #1, 28 May 2024 
• AC1: 'Reply on RC1', Jaroslav Klokocnik, 06 Jun 2024  
• CC1: 'Comment on egusphere-2024-866', Lev Eppelbaum, 07 Jul 2024 
• AC2: 'Reply on CC1', Jaroslav Klokocnik, 08 Jul 2024 
• RC2: 'Comment on egusphere-2024-866', Anonymous Referee #2, 25 Sep 2024.

Thank you for your careful review. We improved our manuscript accordingly. Technical note: Here as well as in the revised manuscript, the replies, comments and corrections are in blue colour and in italics.

-----------------------------------

The manuscript entitled “Popigai and Chicxulub craters: 2 multiple impacts and their associated grabens” discusses the possibility of Popigai and Chicxulub impact craters being double or multiple craters and the possible reactivation of weak planes in the vicinity of the impact zone resulting in the formation of graben. The authors have conducted a thorough gravitational analysis of the impact craters in great detail using gravity field model EIGEN 6C4 with GOCE gradiometry data. Overall, the volume of work is impressive and the gravitation data expressed in the figures are easily comprehensible.  Thank you.

However, there are quite a few issues with the discussion and interpretation that needs to be addressed before publication.  Sure, done, the revised text is sent to be posted.



Major Comments



1.    There is a lack of convincing arguments on why the craters are being interpreted as double or multiple craters.

In the case of Popigai, we guess, our arguments are strong enough (3-4 craters lined-up in ES-NW line). It is not so robust for Chicxulub. Principally, it cannot be decisive only  with the aid of the gravity data. More below.

The authors have very briefly touched upon how double or multiple craters form, which needs to be explained further.

We guess it is correct to introduce the recent discussion about this topic shortly. Our gravity aspects can, however, say nearly nothing about the formation, meaning whether one or two impact craters will be created by the forthcoming impactor(s). We observe their final gravity record as evolved in long time.

Our text has been extended:

The gravity aspects cannot themselves decide whether the impactor was a single body or a binary asteroid before its impact on the Earth. Both is possible. As noted above (Sect. 5.1.), there is possibility of break-up of one body (a single asteroid) in the atmosphere or a “flying cluster” of bodies encountering the atmosphere. To create a double crater, components of a binary asteroid should have a big distance (hundred kilometres) because velocity of asteroids in the Solar system is much higher than velocity of a point rotating on the Earth’s surface. Thus, close binaries can hit on one and the same place and create one crater only. The binaries with a big distance of their components are difficult to be observed. We do not refer to the relevant literature (e.g., Durda et al., Polishook et al., Pravec et al), because it is out of our main focus.

There needs to be a discussion on why the smaller craters are not secondary craters but rather formed due to binary asteroids or breakup of asteroids into smaller fragments in the atmosphere.

Our opinion:

On the Earth, with a higher gravity than on the Moon, the situation differs from the Moon. On the Earth, catena is a rare feature. On the Moon, catenae (belts of secondary craters, ejecta) are not exceptional.

The ejecta (smaller secondary craters) on the Earth would be formed in another direction than a series of the impact craters originating along-track of the impacting body (bodies). It is always such a „fan“ from the impact crater roughly into the opposite direction of the falling asteroid(s).

There is an example of Steinheim-Ries double craters in Germany (double crater in a majority of opinions). Flying roughly from W, two craters were generated (the smaller Steinheim first of all and then the bigger Ries) and finally the ejecta (green glass known as moldavits, vltavins) – it can still be found mainly on the territory of SW part of Czech Republic.

Figures: The strike angles at Steinheim-Ries craters (Germany) together with the gravity anomalies computed with the gravity field model EIGEN6C4 (left) and with ETOPO 1 topography (right). Their trend is from ~W to ~E, with a fragmented halo around Ries.

Link to Supplement SM2:https://www.asu.cas.cz/~jklokocn//CHIC-POP24_supplements/

Our text has been modified and extended.

There is also a lack of explanation pertaining to how the authors are interpreting the impact direction. I feel it is important to address and correlate all these points for a more holistic interpretation on the gravity data and its usefulness in deciphering impact phenomenon in planetary bodies. 

As for the direction of the impactor: sometime we can deduce this direction from the direction of the gravity strike angles (Klokočník et al., 2020b). As a good guide, we offer Steinheim-Ries (S2:18). Geologists know that the impactor(s) came roughly from west, creating first the smaller Steinheim, than the bigger Ries. We can verify it independently using the strike angles; they are combed in the ~WE direction, they are skirting around both craters, creating a halo around Ries (see the figure above). For Popigai, in an analogy, we can expect the impactor coming in ES-NW, producing the small(er) crater(s) first, and the biggest, already proven one, as the last, final (Figs. 1b-d, S3:6-21).

A general geological note:

Our interpretation is based mainly on the experience with the formation of impact craters on the Moon. In "Atlas of the Gravity and Magnetic Fields on the Moon" (Klokočník et al., 2022), we have studied the gravity characteristics of dozens of impact craters distributed over the lunar surface. Needless to say, lunar craters are not only numerous, but, except for the oldest mascon-type structures, little altered by later processes, whereas on Earth, erosion often results in root-like structures several kilometres deep or, as in the case of Chicxulub, in phenomena buried beneath younger sediments. This means that we have worked mainly with analogies that are additionally obscured by erosional processes on Earth, and the original gravity signal may be overprinted by other processes such as tectonic activity or selective erosion. Therefore, the aim of this paper is not to provide unequivocal evidence for the existence of additional craters, but probability that they exist and that further field research should tell more.

In the case of the Popigai impact, the gravitational anomalies are arranged roughly in a single line, which in our opinion best corresponds to lunar catenae. These structures will be difficult to prove on Earth because the smaller craters in particular were formed with much lower impact energy. Thus, we can expect that the impact structures were of varying depths and the shallower ones were more affected by erosion. They will therefore appear in the gravimetric record with different intensities, or they may have disappeared completely. The uniqueness of Popigai Crater, in our opinion, is that the entire linear structure most closely resembles a catena as we know it on the Moon.

The situation at Chicxulub Crater is far from clear. Our data suggest the existence of another crater with some non-negligible probability, but it is fair to say that any interpretation is speculative at this stage of the research. However, if field, i.e. borehole, exploration proves its existence and at least partially clarifies the conditions of its formation, we will have more basis for speculating on the nature of the impact. We have already pointed out in the article that the gravity aspects indicate possible presence of the second structure.

1.    The authors’ use of trend and azimuth information is confusing. Some of the trends in the text are hyphenated while others are not. I suggest making all the trend information hyphenated (e.g., N-S, E-W) and azimuth (direction) information non hyphenated (e.g., SE of crater). In that note, I am confused about the SW-SE fault orientation mentioned in the manuscript (pages 8, 14, 19).

Hopefully improved. Not everywhere clear.



Minor Comments

Shortly speaking: we have no objection against these comments, thus we follow your suggestions to correct our text. Thank you.

Page 1



Abstract



Increase the line spacing



Line 19: Rewrite “here the impact craters Chicxulub and Popigai.” as “The improved techniques were applied to study the impact craters Chicxulub and Popigai in this present research.”



Line 21: Both craters are interpreted to be double or multiple craters.



Line 22: Rewrite ‘The both crater formations’ as ‘Formation of both the craters”



Motivation



Line 28: Instead of writing ‘In this journal’ it is better to refer the paper



Lines 28-31: Complex sentence; break the sentence to simpler sentences for better readability



Lines 32-33: Brief description of double and multiple craters needs to be added with references



Page 2



Line 15: Remove ‘indeed’



Line 16: shook → shock



Line 23: If magnetic intensities have not been studied in this paper, please refer publications where it has been studied



Notes on Theoretical Preliminaries



29: remove ’gravity’



Page 3



Lines 8-12: Complex sentence; break the sentence into simpler sentences for better readability



Line 24: Put (Comb) within parenthesis



Line 25: “not combed”



Line 29: Rewrite ‘can shape a halo’ as ‘can take the shape of a halo’



Page 4



Data, computation, and figures



Line 4-5: Refer the theory



Line 10: Rewrite ‘have not access to’ as ‘did not have access to’



Line 14: Rewrite ‘not only a general figure 10 mGal’ as ‘and not only for a general figure of 10 mGal’



Line 16: Mention how worse



Line 19: Mention couple of other measurements within brackets



Line 20:  heights → height



Line 21: Bedmap 2 → Bedmap2



Line 26: Remove the exclamation mark



Page 5



Line 4: ‘corresponding to the ground resolution of 9 km’



Line 19: Any significance of plotting θ in black and white?



Page 6



Artefacts



Lines 12-13: Rewrite ‘correct interpreting the’ as ‘the correct interpretation of’



Line 17: with → has



Line 19: unbelievable → unrealistic



Line 22: Rewrite ‘how well by the data is covered the area of our interest’ as ‘how well the data has covered the area of our interest’



Line 30: he → the



Page 7



Line 1: Moons’ → Moon’s



Line 9: “hidden”



Line 16: “lurk”



Line 17: attack and distort → hamper



Popigai



Line 27: Remove ‘it was’



Page 8



Line 6: Please clarify whether ‘it is’ is referring the crater or the shield



Page 9



Lines 6-7: Please add references



Line 10: Rewrite ‘their fig. 3a’ as ‘(cf. Fig. 3a in Pilkington et al., 2002)’



Line15: Section 6.1 does not have any “notes” on binary asteroids, only a brief mention



Line 17: quite remotely area → remote area 



Line 19-22: Complex sentence, break the sentence into simpler sentences for better readability



Line 24-25: Why mention beforehand what the authors will argue for?



Page 11



Line 24: Rewrite ‘fragmented now due probably to’ as ‘which is presently fragmented, possibly due to’



Line 25: Rewrite ‘not too intensive’ as ‘not with too much intensity’



Line 27: mark → signature



Line 30: lined → aligned



Page 12



Line 4: Rewrite ‘we had not’ as ‘did not have’



Line 5: Begin a new sentence from “With them now……”



Chicxulub



Lines 14-15: Please clarify ‘external forcing event’



Line 27-28: Add references



Page 13



Line 2: “The impact…….”



Line 8: Rewrite “The literature about the Chicxulub crater is really rich: from Alvarez……” as “The literature about the Chicxulub crater is really rich. To mention a few: Alvarez……”



Line 9: Remove …



Line 11: Remove “This is not a review paper to mention all.”



Line 12: Rewrite “in its study” as “in the study of Chicxulub crater”



Line 14: Rewrite “they did not know” as “they were not aware”



Page 14



Line 3: Remove the



Line 21: Clarify ‘strong on land’



Page 15



Fig. 2a: Point to the semi-circular shadows



Page 17



Line 5: Remove ‘reviving’



Page 19



Discussion



Line 30: “basin”



Page 20



Line 9: “trench modified by impact”



Line 12: Refer the following papers-



Wichman, R. W. (1993). Post-impact modification of craters and multi-ring basins on the Earth and Moon by volcanism and crustal failure. Brown University.



Dasgupta, D., Kundu, A., De, K., & Dasgupta, N. (2019). Polygonal impact craters in the Thaumasia Minor, Mars: role of pre-existing faults in their formation. Journal of the Indian Society of Remote Sensing, 47, 257-265.



Zhang, F., Pizzi, A., Ruj, T., Komatsu, G., Yin, A., Dang, Y., ... & Zou, Y. (2023). Evidence for structural control of mare volcanism in lunar compressional tectonic settings. Nature communications, 14(1), 2892.



Line 30: central peak as the first ring



Page 21 

Line 16: Meantime → In the meantime

Citation: https://doi.org/10.5194/egusphere-2024-866-RC2

The End of rebuttal letter.

Jaroslav Klokočník with co-authors

The End of message

Rebuttal letter. Reply of the authors to the second review to:

Popigai and Chicxulub craters: multiple impacts and their associated grabens

Jaroslav Klokocnik, Vaclav Cilek, Jan Kostelecky, and Ales Bezdek

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor |

• RC1: 'Comment on egusphere-2024-866', Anonymous Referee #1, 28 May 2024 
• AC1: 'Reply on RC1', Jaroslav Klokocnik, 06 Jun 2024  
• CC1: 'Comment on egusphere-2024-866', Lev Eppelbaum, 07 Jul 2024 
• AC2: 'Reply on CC1', Jaroslav Klokocnik, 08 Jul 2024 
• RC2: 'Comment on egusphere-2024-866', Anonymous Referee #2, 25 Sep 2024.

Thank you for your careful review. We improved our manuscript accordingly. Technical note: Here as well as in the revised manuscript, the replies, comments and corrections are in blue colour and in italics.

-----------------------------------

The manuscript entitled “Popigai and Chicxulub craters: 2 multiple impacts and their associated grabens” discusses the possibility of Popigai and Chicxulub impact craters being double or multiple craters and the possible reactivation of weak planes in the vicinity of the impact zone resulting in the formation of graben. The authors have conducted a thorough gravitational analysis of the impact craters in great detail using gravity field model EIGEN 6C4 with GOCE gradiometry data. Overall, the volume of work is impressive and the gravitation data expressed in the figures are easily comprehensible.  Thank you.

However, there are quite a few issues with the discussion and interpretation that needs to be addressed before publication.  Sure, done, the revised text is sent to be posted.



Major Comments



1.    There is a lack of convincing arguments on why the craters are being interpreted as double or multiple craters.

In the case of Popigai, we guess, our arguments are strong enough (3-4 craters lined-up in ES-NW line). It is not so robust for Chicxulub. Principally, it cannot be decisive only  with the aid of the gravity data. More below.

The authors have very briefly touched upon how double or multiple craters form, which needs to be explained further.

We guess it is correct to introduce the recent discussion about this topic shortly. Our gravity aspects can, however, say nearly nothing about the formation, meaning whether one or two impact craters will be created by the forthcoming impactor(s). We observe their final gravity record as evolved in long time.

Our text has been extended:

The gravity aspects cannot themselves decide whether the impactor was a single body or a binary asteroid before its impact on the Earth. Both is possible. As noted above (Sect. 5.1.), there is possibility of break-up of one body (a single asteroid) in the atmosphere or a “flying cluster” of bodies encountering the atmosphere. To create a double crater, components of a binary asteroid should have a big distance (hundred kilometres) because velocity of asteroids in the Solar system is much higher than velocity of a point rotating on the Earth’s surface. Thus, close binaries can hit on one and the same place and create one crater only. The binaries with a big distance of their components are difficult to be observed. We do not refer to the relevant literature (e.g., Durda et al., Polishook et al., Pravec et al), because it is out of our main focus.

There needs to be a discussion on why the smaller craters are not secondary craters but rather formed due to binary asteroids or breakup of asteroids into smaller fragments in the atmosphere.

Our opinion:

On the Earth, with a higher gravity than on the Moon, the situation differs from the Moon. On the Earth, catena is a rare feature. On the Moon, catenae (belts of secondary craters, ejecta) are not exceptional.

The ejecta (smaller secondary craters) on the Earth would be formed in another direction than a series of the impact craters originating along-track of the impacting body (bodies). It is always such a „fan“ from the impact crater roughly into the opposite direction of the falling asteroid(s).

There is an example of Steinheim-Ries double craters in Germany (double crater in a majority of opinions). Flying roughly from W, two craters were generated (the smaller Steinheim first of all and then the bigger Ries) and finally the ejecta (green glass known as moldavits, vltavins) – it can still be found mainly on the territory of SW part of Czech Republic.

Figures: The strike angles at Steinheim-Ries craters (Germany) together with the gravity anomalies computed with the gravity field model EIGEN6C4 (left) and with ETOPO 1 topography (right). Their trend is from ~W to ~E, with a fragmented halo around Ries.

Link to Supplement SM2:https://www.asu.cas.cz/~jklokocn//CHIC-POP24_supplements/

Our text has been modified and extended.

There is also a lack of explanation pertaining to how the authors are interpreting the impact direction. I feel it is important to address and correlate all these points for a more holistic interpretation on the gravity data and its usefulness in deciphering impact phenomenon in planetary bodies. 

As for the direction of the impactor: sometime we can deduce this direction from the direction of the gravity strike angles (Klokočník et al., 2020b). As a good guide, we offer Steinheim-Ries (S2:18). Geologists know that the impactor(s) came roughly from west, creating first the smaller Steinheim, than the bigger Ries. We can verify it independently using the strike angles; they are combed in the ~WE direction, they are skirting around both craters, creating a halo around Ries (see the figure above). For Popigai, in an analogy, we can expect the impactor coming in ES-NW, producing the small(er) crater(s) first, and the biggest, already proven one, as the last, final (Figs. 1b-d, S3:6-21).

A general geological note:

Our interpretation is based mainly on the experience with the formation of impact craters on the Moon. In "Atlas of the Gravity and Magnetic Fields on the Moon" (Klokočník et al., 2022), we have studied the gravity characteristics of dozens of impact craters distributed over the lunar surface. Needless to say, lunar craters are not only numerous, but, except for the oldest mascon-type structures, little altered by later processes, whereas on Earth, erosion often results in root-like structures several kilometres deep or, as in the case of Chicxulub, in phenomena buried beneath younger sediments. This means that we have worked mainly with analogies that are additionally obscured by erosional processes on Earth, and the original gravity signal may be overprinted by other processes such as tectonic activity or selective erosion. Therefore, the aim of this paper is not to provide unequivocal evidence for the existence of additional craters, but probability that they exist and that further field research should tell more.

In the case of the Popigai impact, the gravitational anomalies are arranged roughly in a single line, which in our opinion best corresponds to lunar catenae. These structures will be difficult to prove on Earth because the smaller craters in particular were formed with much lower impact energy. Thus, we can expect that the impact structures were of varying depths and the shallower ones were more affected by erosion. They will therefore appear in the gravimetric record with different intensities, or they may have disappeared completely. The uniqueness of Popigai Crater, in our opinion, is that the entire linear structure most closely resembles a catena as we know it on the Moon.

The situation at Chicxulub Crater is far from clear. Our data suggest the existence of another crater with some non-negligible probability, but it is fair to say that any interpretation is speculative at this stage of the research. However, if field, i.e. borehole, exploration proves its existence and at least partially clarifies the conditions of its formation, we will have more basis for speculating on the nature of the impact. We have already pointed out in the article that the gravity aspects indicate possible presence of the second structure.

1.    The authors’ use of trend and azimuth information is confusing. Some of the trends in the text are hyphenated while others are not. I suggest making all the trend information hyphenated (e.g., N-S, E-W) and azimuth (direction) information non hyphenated (e.g., SE of crater). In that note, I am confused about the SW-SE fault orientation mentioned in the manuscript (pages 8, 14, 19).

Hopefully improved. Not everywhere clear.



Minor Comments

Shortly speaking: we have no objection against these comments, thus we follow your suggestions to correct our text. Thank you.

Page 1



Abstract



Increase the line spacing



Line 19: Rewrite “here the impact craters Chicxulub and Popigai.” as “The improved techniques were applied to study the impact craters Chicxulub and Popigai in this present research.”



Line 21: Both craters are interpreted to be double or multiple craters.



Line 22: Rewrite ‘The both crater formations’ as ‘Formation of both the craters”



Motivation



Line 28: Instead of writing ‘In this journal’ it is better to refer the paper



Lines 28-31: Complex sentence; break the sentence to simpler sentences for better readability



Lines 32-33: Brief description of double and multiple craters needs to be added with references



Page 2



Line 15: Remove ‘indeed’



Line 16: shook → shock



Line 23: If magnetic intensities have not been studied in this paper, please refer publications where it has been studied



Notes on Theoretical Preliminaries



29: remove ’gravity’



Page 3



Lines 8-12: Complex sentence; break the sentence into simpler sentences for better readability



Line 24: Put (Comb) within parenthesis



Line 25: “not combed”



Line 29: Rewrite ‘can shape a halo’ as ‘can take the shape of a halo’



Page 4



Data, computation, and figures



Line 4-5: Refer the theory



Line 10: Rewrite ‘have not access to’ as ‘did not have access to’



Line 14: Rewrite ‘not only a general figure 10 mGal’ as ‘and not only for a general figure of 10 mGal’



Line 16: Mention how worse



Line 19: Mention couple of other measurements within brackets



Line 20:  heights → height



Line 21: Bedmap 2 → Bedmap2



Line 26: Remove the exclamation mark



Page 5



Line 4: ‘corresponding to the ground resolution of 9 km’



Line 19: Any significance of plotting θ in black and white?



Page 6



Artefacts



Lines 12-13: Rewrite ‘correct interpreting the’ as ‘the correct interpretation of’



Line 17: with → has



Line 19: unbelievable → unrealistic



Line 22: Rewrite ‘how well by the data is covered the area of our interest’ as ‘how well the data has covered the area of our interest’



Line 30: he → the



Page 7



Line 1: Moons’ → Moon’s



Line 9: “hidden”



Line 16: “lurk”



Line 17: attack and distort → hamper



Popigai



Line 27: Remove ‘it was’



Page 8



Line 6: Please clarify whether ‘it is’ is referring the crater or the shield



Page 9



Lines 6-7: Please add references



Line 10: Rewrite ‘their fig. 3a’ as ‘(cf. Fig. 3a in Pilkington et al., 2002)’



Line15: Section 6.1 does not have any “notes” on binary asteroids, only a brief mention



Line 17: quite remotely area → remote area 



Line 19-22: Complex sentence, break the sentence into simpler sentences for better readability



Line 24-25: Why mention beforehand what the authors will argue for?



Page 11



Line 24: Rewrite ‘fragmented now due probably to’ as ‘which is presently fragmented, possibly due to’



Line 25: Rewrite ‘not too intensive’ as ‘not with too much intensity’



Line 27: mark → signature



Line 30: lined → aligned



Page 12



Line 4: Rewrite ‘we had not’ as ‘did not have’



Line 5: Begin a new sentence from “With them now……”



Chicxulub



Lines 14-15: Please clarify ‘external forcing event’



Line 27-28: Add references



Page 13



Line 2: “The impact…….”



Line 8: Rewrite “The literature about the Chicxulub crater is really rich: from Alvarez……” as “The literature about the Chicxulub crater is really rich. To mention a few: Alvarez……”



Line 9: Remove …



Line 11: Remove “This is not a review paper to mention all.”



Line 12: Rewrite “in its study” as “in the study of Chicxulub crater”



Line 14: Rewrite “they did not know” as “they were not aware”



Page 14



Line 3: Remove the



Line 21: Clarify ‘strong on land’



Page 15



Fig. 2a: Point to the semi-circular shadows



Page 17



Line 5: Remove ‘reviving’



Page 19



Discussion



Line 30: “basin”



Page 20



Line 9: “trench modified by impact”



Line 12: Refer the following papers-



Wichman, R. W. (1993). Post-impact modification of craters and multi-ring basins on the Earth and Moon by volcanism and crustal failure. Brown University.



Dasgupta, D., Kundu, A., De, K., & Dasgupta, N. (2019). Polygonal impact craters in the Thaumasia Minor, Mars: role of pre-existing faults in their formation. Journal of the Indian Society of Remote Sensing, 47, 257-265.



Zhang, F., Pizzi, A., Ruj, T., Komatsu, G., Yin, A., Dang, Y., ... & Zou, Y. (2023). Evidence for structural control of mare volcanism in lunar compressional tectonic settings. Nature communications, 14(1), 2892.



Line 30: central peak as the first ring



Page 21 

Line 16: Meantime → In the meantime

Citation: https://doi.org/10.5194/egusphere-2024-866-RC2

The End of rebuttal letter.

Jaroslav Klokočník with co-authors

The End of message