Geodetic Upper Crust Deformation Based on Primary GNSS and INSAR Data in the Strymon Basin, Northern Greece—Correlation with Active Faults

Round 1

Reviewer 1 Report

This is an interesting paper and is overall well written.

My major concern is with the chapter 4 which has to be considerably improved. In this chapter there is several connection to basic 2D mechanics. However, the reader can't comprehend this.

All deformations in the plane can be expressed by strain tensor (in 2D, this consist of two normal components and one shear component). The tensor can be transformed by the rotation of the coordinate system to obtain the principle values i.e. max and. min strains. In this orientation the shear component is equal zero. There is a number of basic textbooks describing this. In the paper some very basic things are explaind in detail (the use of Pitagorean Theorem) whereas some basic notaions of basic linea mechanics is missing. 

The term "Area strain" is unusual. This is just the change of area.

The term "total velocity" is missleading, this is just basic velocity, nothing more.

The terms shear (or lack of shear) is connected to ductile properties which have nothing to do with shear. You can have shear in ductile or brittle material. Irrelevant!

The unit "nano-strain" is used throughout the paper. This is not a unit. Nano is just a prefix for 10^-9, strain is a mechanical variable not a unit. There should be just a notiation, that the values should be multiplied by 10^-9 to obtain the actual strain.

There are som minor suggestions included in the attached file.

Comments for author File: Comments.pdf

Author Response

Reviewer 1#

This is an interesting paper and is overall well written.

My major concern is with the chapter 4 which has to be considerably improved. In this chapter there is several connection to basic 2D mechanics. However, the reader can't comprehend this.

All deformations in the plane can be expressed by strain tensor (in 2D, this consist of two normal components and one shear component). The tensor can be transformed by the rotation of the coordinate system to obtain the principle values i.e. max and. min strains. In this orientation the shear component is equal zero. There is a number of basic textbooks describing this. In the paper some very basic things are explaind in detail (the use of Pitagorean Theorem) whereas some basic notaions of basic linea mechanics is missing.

The term "Area strain" is unusual. This is just the change of area.

The term "total velocity" is missleading, this is just basic velocity, nothing more.

The terms shear (or lack of shear) is connected to ductile properties which have nothing to do with shear. You can have shear in ductile or brittle material. Irrelevant!

The unit "nano-strain" is used throughout the paper. This is not a unit. Nano is just a prefix for 10^-9, strain is a mechanical variable not a unit. There should be just a notiation, that the values should be multiplied by 10^-9 to obtain the actual strain.

There are som minor suggestions included in the attached file.

Answer to Reviewer 1#

We would like to thank Reviewer 1# for the fruitful, well-aimed comments which definitely improved the manuscript. We addressed to each and every comment following the reviewer’s suggestions. In particular:

Comment 1: “All deformations in the plane can be expressed by strain tensor (in 2D, this consist of two normal components and one shear component). The tensor can be transformed by the rotation of the coordinate system to obtain the principle values i.e. max and. min strains. In this orientation the shear component is equal zero. There is a number of basic textbooks describing this. In the paper some very basic things are explaind in detail (the use of Pitagorean Theorem) whereas some basic notaions of basic linea mechanics is missing.”

Answer to Comment 1: Chapter 4 was modified, considering the Reviewer 1# comments, included in the pdf file. In particular, the mathematical equations were clarified, while additional details (Pythagorean Theorem) were removed.

Comment 2: “The term "Area strain" is unusual. This is just the change of area.”

Answer to Comment 2: The "Area strain" term is proposed by the software package, so we should maintain it. An alternative term, which describes this strain parameter in other papers, is “Dilatation”. However, Dilatation is one type of Area Strain (positive Area Strain); Compaction is the second type (negative Area Strain). Both Dilatation and Compaction are described in detail in our manuscript.

Comment 3: “The term "total velocity" is missleading, this is just basic velocity, nothing more.”

Answer to Comment 3: The term “Total Velocity” was replaced with the term “Velocity” throughout the manuscript.

Comment 4: “The terms shear (or lack of shear) is connected to ductile properties which have nothing to do with shear. You can have shear in ductile or brittle material. Irrelevant!”

Answer to Comment 4: This part was removed. In particular, the phrase “…are mainly associated with ductile (or semi-ductile) compressional tectonic activity.” was modified into “…are mainly associated with compressional tectonic activity.”

Comment 5: “The unit "nano-strain" is used throughout the paper. This is not a unit. Nano is just a prefix for 10^-9, strain is a mechanical variable not a unit. There should be just a notiation, that the values should be multiplied by 10^-9 to obtain the actual strain.”

Answer to Comment 5: The unit “nano-strain” is not an SI unknit, as you mentioned in the text. We removed it throughout the manuscript, adding “  10^-9” after each value.

Comment 6: “There are som minor suggestions included in the attached file.”

Answer to Comment 6: We took into consideration almost the total of your suggestions, included in the manuscript. In particular, we did not include a Triangulation Figure, as the great number of triangles (216 triangles) result in a confusing and a blur image. If you track any unintentional omissions, we will be glad to consider them.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript describes the seismo-tectonics and crustal deformations of an area located in Central-Eastern Macedonia (Greece). The analysis is mainly based on GNSS and PS InSAR observations joined with the knowledge of faults and seismicity.

General Remarks: Although the manuscript is well organized as sections, the text goes too far in in some parts while it neglects others, moreover some references are nowadays outdated by more recent ones. The time span of GNSS observations is dated (8 years ago !) and does not coincide with the PS time interval, thus preventing any direct comparison. It is not clear whether the authors processed the data by themselves or not, if so the results from GNSS analysis is completely missing. Suggestions:   1)      Clarify the GNSS processing explaining the way to obtain the daily solutions, the frame realization and the velocities with their errors. Are the velocities obtained from a joint solution of all the sites and whole covariance matrices? Please, provide a table with velocities and uncertainties. Add a figure with the velocities of all the sites with error ellipses. 2)      The triangulation methodology to estimate strain/ strain rate is rather classical and already explained in other works of the same first author, therefore it should be reduced drastically by providing only the appropriate references. 3)      It is more important to add the errors of the total velocity to the map, and in the text as average value. The total velocity represents the translation velocity of the triangle centroid, so pay attention to use strain rate instead of strain, to avoid confusion with displacements and strain. The software provided by UNAVCO is able to give also the uncertainties of the computed strain, strain rate components, pleas add them at least as maximum and minimum or average value. 4)      Compare the strain rate results with those obtained in recent papers like Kreemer C., G. Blewitt, and E. C. Klein (2014), A geodetic plate motion and Global Strain Rate Model, Geochem. Geophys. Geosyst.,15, 3849–3889,doi:10.1002/2014GC005407, and others. 5)      If the authors processed the GNSS data, they can project the coordinate components along the LoS of PS time series, to try to compare the two time series, even if during different time intervals. 6)      Remove all the references which have been overcome by more recent papers, they make the paper hard to read and not updated. Many of the references published before 2010 have been already mentioned by more recent papers already in the list, so it is not useful to include them again.  Final comment: The manuscript has a good chance of reaching a very good level if the authors feel like it. At present, the paper needs in my opinion major revisions, but it can be easily improved if the authors have processed all the data by themselves.

Author Response

Reviewer 2#

The manuscript describes the seismo-tectonics and crustal deformations of an area located in Central-Eastern Macedonia (Greece). The analysis is mainly based on GNSS and PS InSAR observations joined with the knowledge of faults and seismicity.

General Remarks: Although the manuscript is well organized as sections, the text goes too far in in some parts while it neglects others, moreover some references are nowadays outdated by more recent ones. The time span of GNSS observations is dated (8 years ago !) and does not coincide with the PS time interval, thus preventing any direct comparison. It is not clear whether the authors processed the data by themselves or not, if so the results from GNSS analysis is completely missing. Suggestions:   1)      Clarify the GNSS processing explaining the way to obtain the daily solutions, the frame realization and the velocities with their errors. Are the velocities obtained from a joint solution of all the sites and whole covariance matrices? Please, provide a table with velocities and uncertainties. Add a figure with the velocities of all the sites with error ellipses. 2)      The triangulation methodology to estimate strain/ strain rate is rather classical and already explained in other works of the same first author, therefore it should be reduced drastically by providing only the appropriate references. 3)      It is more important to add the errors of the total velocity to the map, and in the text as average value. The total velocity represents the translation velocity of the triangle centroid, so pay attention to use strain rate instead of strain, to avoid confusion with displacements and strain. The software provided by UNAVCO is able to give also the uncertainties of the computed strain, strain rate components, pleas add them at least as maximum and minimum or average value. 4)      Compare the strain rate results with those obtained in recent papers like Kreemer C., G. Blewitt, and E. C. Klein (2014), A geodetic plate motion and Global Strain Rate Model, Geochem. Geophys. Geosyst.,15, 3849–3889,doi:10.1002/2014GC005407, and others. 5)      If the authors processed the GNSS data, they can project the coordinate components along the LoS of PS time series, to try to compare the two time series, even if during different time intervals. 6)      Remove all the references which have been overcome by more recent papers, they make the paper hard to read and not updated. Many of the references published before 2010 have been already mentioned by more recent papers already in the list, so it is not useful to include them again.  Final comment: The manuscript has a good chance of reaching a very good level if the authors feel like it. At present, the paper needs in my opinion major revisions, but it can be easily improved if the authors have processed all the data by themselves.

Answer to Reviewer 2#

We would like to thank Reviewer 2# for the fruitful, well-aimed comments which definitely improved the manuscript. We addressed to each and every comment following the reviewer’s suggestions. In particular:

Comment 1: “Clarify the GNSS processing explaining the way to obtain the daily solutions, the frame realization and the velocities with their errors. Are the velocities obtained from a joint solution of all the sites and whole covariance matrices? Please, provide a table with velocities and uncertainties. Add a figure with the velocities of all the sites with error ellipses.”

Answer to Comment 1: Done. The GNSS processing and the explanation of the way to obtain the daily solutions are analyzed. In particular, we added the paragraph “Regarding the geodetic velocity calculation, a 7-year (2008 - 2014) interval was analyzed, while the data recording…. velocities of the processed permanent GNSS sites relative to ETRF2000.”, which also includes the mathematical background. Moreover, we added a table (Table 1) with the velocities and the uncertainties. However, we did not add a Figure with the velocities and error ellipses, as a similar Figure has already been included in the manuscript (Figure 5).

Comment 2: “The triangulation methodology to estimate strain/ strain rate is rather classical and already explained in other works of the same first author, therefore it should be reduced drastically by providing only the appropriate references.”

Answer to Comment 2: Done. The triangulation methodology description was reduced drastically in the manuscript, while the appropriate references are included. The analytical description was moved in the Supplementary Materials.

Comment 3: “It is more important to add the errors of the total velocity to the map, and in the text as average value. The total velocity represents the translation velocity of the triangle centroid, so pay attention to use strain rate instead of strain, to avoid confusion with displacements and strain. The software provided by UNAVCO is able to give also the uncertainties of the computed strain, strain rate components, pleas add them at least as maximum and minimum or average value.”

Answer to Comment 3: We totally understand the importance of errors of the total velocity (renamed velocity, according to Reviewer 1# comments) and we would already have added it in the manuscript. However, the GPS triangular Calculator software, provided by UNAVCO does not provide the ability of calculating the error of the total velocity. The E and N velocity components (and the corresponding uncertainties) can be calculated for each triangle; however, we do not include them, as we have already provided the recorded E and N velocity components (and the corresponding uncertainties), based on your comments (Comment 1). Regarding the computed strain components (e_xx, e_xy, e_yy) and the corresponding uncertainties, a table (Table 2) was added, including the maximum, minimum and average values, as you proposed.

Comment 4: “Compare the strain rate results with those obtained in recent papers like Kreemer C., G. Blewitt, and E. C. Klein (2014), A geodetic plate motion and Global Strain Rate Model, Geochem. Geophys. Geosyst.,15, 3849–3889,doi:10.1002/2014GC005407, and others.”

Answer to Comment 4: Done. We have already included a comparison with the strain rate results, obtained in recent papers in the “Discussion” section. However, the paper by Kreemer et al. (2014) was not initially included; it was fixed by citing the aforementioned reference.

Comment 5: “If the authors processed the GNSS data, they can project the coordinate components along the LoS of PS time series, to try to compare the two time series, even if during different time intervals.”

Answer to Comment 5: Done. An additional Figure is included in the Supplementary Materials, showing the Intercomparison between GNSS and InSAR annual motion rates (vertical component), for GNSS sites located over the InSAR processing extend.

Comment 6: “Remove all the references which have been overcome by more recent papers, they make the paper hard to read and not updated. Many of the references published before 2010 have been already mentioned by more recent papers already in the list, so it is not useful to include them again.”

Answer to Comment 6: We agree that numerous references have been included in the manuscript, as well as the fact that the paper may be harder to read; however, all references are relative to the subject of our paper. Regardless of the fact that many of the references published before 2010 have already been mentioned by more recent papers, included in the list, we believe that these papers should also be cited, acknowledging the previous studies, related to our work. We would be glad to include additional, more recent references, related to our paper, which are probably missing.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Ok, all the major requested improvements were done. Please check Table 2: one of the value missed the decimal dot.

About uncertainties of total velocities they are not hard to compute from the uncertainties of velocity components through the propagation error formula.

 After these last considerations, in my opinion the manuscript can be accepted in the present form, the text editing can be done on the proofs