The Mw = 5.6 Kanallaki Earthquake of 21 March 2020 in West Epirus, Greece: Reverse Fault Model from InSAR Data and Seismotectonic Implications for Apulia-Eurasia Collision

Round 1

Reviewer 1 Report

I saw that the Authors skipped almost all the important points of my concern.

• Geological and structural setting: is almost lacking. no reliable geological sections are presented. this is subtracting meaning to the findings of the Authors. they replied that no geological maps boreholes etc are available and thus did not considered this point.
• I still think that the fixed parameters ofr the inversion process are too many and this choice is not necessarily justified by external data. e.g., the Authors choose the low angle nodal plane beacause: i) the other one is steeply dipping, and ii) no backthrusts are traced in geological maps. but this is contradictory: i) backthrusts are usually more steep than forethrusts and ii) the Athors stated that no reliable geological maps are available - thus making assumptions on not reliable data is a shortcoming.

many minor points were fixed but the importt ones still remain over there...

I'm suggesting minor revisions at this round but I think that now the decision should be on the Editor's shoulder considering that my doubts were not faced in the Authors' answer.

best regards.

Author Response

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Geological and structural setting: is almost lacking. no reliable geological sections are presented. this is subtracting meaning to the findings of the Authors. they replied that no geological maps boreholes etc are available and thus did not considered this point.

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We understand the point of view of the reviewer however, we have taken into account published geological maps, dozens of papers, our own findings and other literature (see references section of the paper; especially references 1-17) so that we can document our geological interpretation and suggest the Margariti thrust fault as the host structure of the March 21, 2020 earthquake. In our first response letter we also stated that during the month of September 2020 we made a search with oil companies that are currently investigating the subsurface of Epirus, however, we did not manage to find new data (cross-sections or drilling data).

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I still think that the fixed parameters ofr the inversion process are too many and this choice is not necessarily justified by external data.

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Indeed, we fixed several of the fault parameters for the inversion. This is because of the amplitude of the deformation and the « rhomb » shape of the fringe pattern that does not allow to retrieve well the azimuth and dip angle of the fault from the geodetic data.

We agree with the reviewer that the most critical parameter is the choice of the fault plane.

Concerning the hypothesis of the antithetic plane, in our paper this hypothesis is not rejected primarily on the basis of the interferograms but on the basis of geological & seismological considerations. As the fault is not very shallow, the magnitude is only M=5.6 and the dip angle not very different from 45°, the two conjugate planes produce modeled interferograms that are very similar to each other, and therefore InSAR does not have the capability to discriminate.

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the Authors choose the low angle nodal plane beacause: i) the other one is steeply dipping

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Yes, there is a difference of 14 degrees in the mean dip-angle between the two planes according to seismology (see Table 3 in the revised manuscript).

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and ii) no backthrusts are traced in geological maps.

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Yes, this is the main reason (based on geology). However, please note that the InSAR data and all other data of that earthquake do not bring new elements that contradict this vision.

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but this is contradictory: i) backthrusts are usually more steep than forethrusts and ii)

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Yes, we agree, but anyway in the particular case of Kanallaki the two angles are not very different (see reply above).

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the Athors stated that no reliable geological maps are available - thus making assumptions on not reliable data is a shortcoming.

No, we said that all geological maps in western Epirus show west-verging thrusts as the main structures! We did not say that the maps are unreliable.

TBD (Sotiris & Thanassis)

Author Response File: Author Response.doc

Reviewer 2 Report

I am now satisfied with the author's responses and happy to suggest it being published. 

Author Response

Many thanks for your review comments

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Valkaniotis et al. Discuss geodetic and seismological data for a sector hit by the Mw 5.6 2020 earthquake. I appreciated the integrated approach, but I found some major shortcomings on this work that I’m summarizing below:

• Paper structure should be revised providing a Methods and a Discussion section.
• Most of the methods are mostly clearly described but details are lacking for some of the (e.g., on the GPS processing);  the different  InSAR inversions should be described.
• The authors assume many of the variables for InSAR inversion from seismological analysis or from regional geology. This resulted in strongly limiting the possible output from inversion. The obtained result is an odd square fault (5 x 5 km), almost blind, with too much displacement obtained if compared to empirical regression laws. Fault shape should be discussed from the structural point of view and compared with other known faults. Probably alternative faults solutions should be considered. The supposed correlation with the Margariti fault is questionable but a reliable geologic cross-section with the structure projected upon is lacking.
• GPS data analysis puts the earthquake in a zone of relatively low strain rate. But this and other previous events hit as far as 80 km from the deformation zone. A discussion of these apparently contradictory evidence should be provided.

You’ll find attached a manuscript with many notes and other minor points.

Comments for author File: Comments.pdf

Reviewer 2 Report

Very interesting paper!

My comments and proposed editing are found in the attached file.

In the supplementary doc, I found only the need to correct table S3 (Easting and Northing instead of Long and Lat) and to add degrees and meters in table S4

Comments for author File: Comments.pdf

Reviewer 3 Report

The paper entitled “The Mw = 5.6 Kanallaki earthquake of March 21, 2020 in west Epirus, Greece: reverse fault model from InSAR data and seismotectonic implications for Apulia-Eurasia collision” analysed the Kanallaki earthquake in great detail using a combination of geodetic and seismological datasets. The paper is well structured, and the result is convincing. It is worth publishing if the author can address the following questions:

Line 38: indicate where is Apulian continental block and where is the Eurasian plate in Figure 1.

Line 60-64: you don’t have to list your results in the Introduction, instead you should spend more text on the background of this earthquake.

Line 82: I would not say a Mw 3.8 earthquake is a moderate sized earthquake. It is only a small aftershock.

Line 190-191: the tropospheric effect is hardly a decorrelation factor. In most cases the tropospheric delay will not result in decorrelation. Please address this properly and include appropriate references.

Line 196: How can you be sure that the tropospheric effect is low?

Line 197: “is also good.” Good of what? Same for Line 199.

Line 205: to be clear, they are not in opposite directions.

Line 204-210: given that the co-seismic signal on interferograms is relatively small for this event, the tropospheric effect may contribute a lot. Therefore, how is the tropospheric effect being dealt with? Have you applied any corrections or remove some empirical-based phase contributions?

Line 214: weak magnitude -> small magnitude

Line 315: how is the upper edge of the fault being defined? The co-seismic geodetic observation won’t tell you the whole fault geometry, only the portion that slipped during the mainshock is revealed by them. This event may not necessarily rupture the whole segment of the fault.