Morphotectonic Structures along the Southwestern Margin of Lesvos Island, and Their Interrelation with the Southern Strand of the North Anatolian Fault, Aegean Sea, Greece

Round 1

Reviewer 1 Report

Thibault CAVAILHES                                                                                                        Manuscript number 1468034

UMR CNRS 5805 EPOC - OASU
Université de Bordeaux
Site de Talence - Bâtiment B18N
Allée Geoffroy Saint-Hilaire
CS 50023
33615 PESSAC CEDEX
FRANCE

Dear authors,

I read your manuscript entitled “Morphotectonic structures long the southwestern margin of Lesvos Island, and their interrelation with the southern strand of the North Anatolian fault, Aegean Sea, Greece” with great interest. The offshore structural morphologies you describe are intriguing and clearly deserve publication. However, three main points should be addressed before publishing these data. I wish all the best to the authors to slightly revise their manuscript.

1 – BATHYMETRY AND MAPPING

5. The fault trace related to the fault scarp is remarkably sinuous ( 6). This fault trace can be explained by low angle dipping normal fault as you suggest, but how about its segmentation? The fault ramp (relay, fig. 5c) seems close to the Mw 5.2 earthquake for instance, therefore showing that fault segmentation has strong implications on potential earthquake magnitudes. Could you better address the fault segmentation, providing quantitative graphics on fault length for instance?
6. How do you interpret the high density of northward dipping normal faults at 25.50.0°E and 39°00? This architectural change in structural style would reflect a change in underlying mechanics, thermal regime, fault connectivity to the main dipping southward normal fault? Are they antithetic/conjugate normal faults of the main fault?
7. Could you provide accurate stereoplot (rose diagrams) of the structural lineaments you have mapped?

2 – RELATIONS WITH ONSHORE GEOLOGY

1. The onshore geology of the Lesvos Island is almost completely missing. The ages of fault activity, the ages of reactivation, the fault strikes, the faults dips, the chronologies between the different fault sets have to be stated and compared to the offshore data (rose diagram and stereoplot).
2. I am not really used with the local geology but I am surprised that the NE-SW active strike-slip fault (onshore Kalloni-Aghia-Paraskevi dextral fault) does not have any expression in southern offshore areas. Why this structure is limited to the island? Usually, tectonics does not stopped at the shoreline. I have added a comment to the figure 4a where at least two NE-SW lineaments clearly modify the shape of the NW-SE normal faults sets in offshore areas. Please, could you double-check this?

Examples of onshore structural lineaments mapping in Lesvos island (Novak and Soulakellis, 2000, Geomorphology): “Lineaments detected in this study were coincident with: 1 mapped contacts or faults, 2 extensions of previously mapped faults or 3 previously undetected geologic features including faults, tectonic contacts or formational contacts”. The structural lineaments strikes in the studied offshore areas seem similar to this… Please, double-check.

The authors should better contextualize their work with onshore previous structural works. Two examples are given below.

Vacchi et al., 2012, Geomorphology

Novak and Soulakellis, 2000, Geomorphology

3- VERTICAL CROSS-SECTION ANALYSIS

6. I am surprised that the authors do not provide a qualitative NE-SW cross-section of the area. I think that this can be sketched on figure 6.
7. I assume that regional seismic profiles are not available.

4 – REGIONAL GEOLOGY

1. I agree, the northern part of the Lesvos island is into a pull-apart. However, the southern part of the Lesvos Island (Lesvos basin) would not be into a pull-apart because this area is clearly out of the extensional relays of the strike-slip system. I would call this an “extensional quadrant” or “wing structure”, or a extensional quadrant related to strike-slip curvature (curvature deformation). This latter case could be relevant if the deformation is quicker on the Skyros fault rather than the Edremit fault (differential movement).
2. The missing point to me is the chronology between the faults sets at the geological time scale using onshore data. Normal faults have to be synchronous with strike-slip deformation at the geolocical time scale (long-term), at not only the main shock and the aftershocks timescale (short-term: the aftershocks using the mechanical discontinuities that are available in the area).

Again, all the best to the authors to modify the manuscript. I have downloaded the manuscript with my comments (pdf).

Kindest regards,

Comments for author File: Comments.zip

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Overall, I find the manuscript interesting, well written and with nice illustrations. However, it is not clear what is new in this study and what it is already published in another recent work by the same authors, so I recommend a moderate revision of the work before acceptance. This revision should clearly state what is new in this study in comparison to their recently published paper, and it should result in a significantly shorter version of the paper by removing the results and interpretations that have already presented in their other paper (referencing the other paper more regularly is also strongly recommended).

Please see below for more specific comments:

1) Are the data publicly available and, if yes, how someone can access them? Could you please provide a statement about data availability?

2) In most of the figures the basin axes are highlighted. Could you please provide a definition of what is the basin axis? Could you also please clarify on which data the interpretation of the basin axes is based and why is it important to included it in most of the maps? For example some of the maps include only the basin axes but not the faults that are responsible for the formation of the basins.

3) Please make sure that the North arrow is included in all maps. Please indicate the locations of the basins in figs 4, 6 and 7 as it is done in fig. 3.

4) lines 15-21 (in abstract and the corresponding ones in the full-text): What is the difference between this and the following paper? 
Nomikou, P., Papanikolaou, D., Lampridou, D., Blum, M. and Hübscher, C., 2021. The active tectonic structures along the southern margin of Lesvos Island, related to the seismic activity of July 2017, Aegean Sea, Greece. Geo-Marine Letters, 41(4), pp.1-11.

5) lines 27-28 (in abstract and the corresponding ones in the full-text): This is an overstatement. The fact that borders the western end of the Lesvos Basin doesn't mean that it controls all the structures, and therefore, the geometry of the southern Lesvos margin as a whole.  

6) lines 29-30 (in abstract and the corresponding ones in the full-text): What is the difference between this and the following paper? 
Nomikou, P., Papanikolaou, D., Lampridou, D., Blum, M. and Hübscher, C., 2021. The active tectonic structures along the southern margin of Lesvos Island, related to the seismic activity of July 2017, Aegean Sea, Greece. Geo-Marine Letters, 41(4), pp.1-11.

7) line 29: the NW-SW disrupting channel --> SE

8) lines 94-96: What about the data presented at the following paper? Please talk about them.
Nomikou, P., Papanikolaou, D., Lampridou, D., Blum, M. and Hübscher, C., 2021. The active tectonic structures along the southern margin of Lesvos Island, related to the seismic activity of July 2017, Aegean Sea, Greece. Geo-Marine Letters, 41(4), pp.1-11.

9) line 223: There are more faults onshore, at the footwall of this fault, that should also be considered in the throw calculations. 
Furthermore and most importantly, before considering the maximum altitude of Olympus mt. as a result of footwall uplift, and therefore, including it in the calculations of the overall throw, I suggest to generate a topographic profile perpendicular to the fault from the Olympus mt to the SM of Lesvos Basin. The shape of this topographic profile will help you to distinguish footwall uplift and hangingwall subsidence from other structures unrelated to the studied normal fault. For example, the shape of the topographic profile from the studied fault to the SM of Lesvos Basin (Fig. 3) is an excellent example of how the hangingwall subsidence should look like, but I am not sure that this is also the case for the topographic profile from the Olympus mt to the studied fault. Please revise your estimates, figures and text accordingly.  

10) line 225 ('which is estimated at several hundred m'): On which data this estimation is based?

Hope this comments are useful.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Having seen the replies to my comments and the revised version of the ms, I would be happy to recommend acceptance and publication in the present form.