Investigation of the Pre- and Co-Seismic Ionospheric Effects from the 6 February 2023 M7.8 Turkey Earthquake by a Doppler Ionosonde

Round 1

Reviewer 1 Report

I have read the manuscript with great interest and found that the manuscript is a significant contribution to the topic only after major revision. There are so many unanswered questions that need to be addressed before it is ready for publishing.

Comments for author File: Comments.pdf

Minor editing of English language required

Author Response

QUESTION #1
Line 32: ‘For the far earthquakes with large epicenter distance... ’ What is the meaning of large epicenter distance? It should be a large preparation zone.

++++ ANSWER:
After an earthquake, the seismic Rayleigh wave moves up to large distance and generates acoustic waves. As the Rayleigh wave achieves the sub-ionospheric point of a Doppler ionosonde, the acoustic waves propagate
by the law of infrasonic wave and reach the height of the ionosphere. The distance between the earthquake epicenter and the sub-ionospheric point may be great. For example, as shown in references [12,13,47], the ionospheric disturbances excited by the 2011 Tohoku earthquake and 2015 Nepal earthquake were registered by a Doppler ionosonde  over the Czech Republic at a distance of the order of 9000km.

QUESTION #2
In the third paragraph of the introduction the authors mentioned TEC anomalies observed before large earthquakes and gave references related to it. But before TEC observations several authors have observed anomalies related to earthquakes using Ionosonde, Very Low Frequency receiver, and Ultra Low frequency receiver. The most prominent anomaly related to VLF wave propagation during and before the earthquake was
observed by Hayakawa et al. (1996a, b) for the famous Kobe earthquake. Biagi et al. (2004) presented the first result from the European VLF network and pointed out the decrease in the intensity of the signal for the IT-Bari propagation path (IT = 54 kHz) for two earthquakes with magnitude 4.3 and 5.6 respectively. In recent years, Chakraborty et al.
(2017) studied VLF anomalies during the 2015 Nepal earthquakes and regenerate the signal amplitude using LWPC and compute electron density before the main shock. Politis et al. (2023) study anomalies possibly related to very recent strong (M > 5.5) earthquakes (EQs) that occurred in the southeastern Mediterranean in September-October 2021 and January 2022. Authors have used the signal transmitted from the Negev in
Israel (29.7 kHz) and received by three VLF/LF receivers installed, at a close distance to each other, in Athens (Greece) to find significant changes in the ionosphere using different types of methods. As the authors are presenting a short review of seismo-ionospheric coupling in the introduction section and presenting ionosonde observations, they should have mentioned not only TEC anomalies but also references related to VLF, ULF, and ionosonde.

++++ ANSWER: 
We took into account your wishes and added the references to the recommended works on VLF and ULF investigation before and in the time of earthquake.

 

QUESTION #3
The authors are dealing with anomalies observed before the M7.8 Turkey earthquake using ionosonde data. In this context, I would suggest the authors include two more references in the introduction part. Instead of presenting Critical frequency (f0F2) directly obtained from ionosonde observations, Ghosh et al. (2017) presented a new parameter computed from Barbier’s airglow equation and contains f0F2 and h’F values to study the possible disturbance in the ionosphere. Later Pulinets et al. (2022) used the same parameter and found that the newly derived parameter is much more efficient for the interpretation of the ionospheric behavior prior to the earthquake.

++++ ANSWER: 
In our present work we did not use the Barbier's parameter $\delta$ for the analysis of ionospheric disturbances an searching for the ionospheric earthquake precursors. Nevertheless, with account of the effectiveness od this method described in Ghosh et al. (2017) и Pulinets, S.A. et al. (2022), it seems interesting to apply the method in our further studies. Much thanks for the recommendation.

QUESTION #4
The authors have mentioned that the first hop point is within the earthquake preparation zone and the related Seismo-acoustic effect in the ionosphere. The second hop point is outside the earthquake preparation zone. How it is affecting the obtained results and playing a role in the seismic acoustic effects?

++++ ANSWER:
The effect in the ionosphere detected by the Doppler ionosonde has appeared as a result of penetration in the ionosphere of the acoustic (infrasonic) waves which were generated by the surface seismic Rayleigh wave. The appearance of such seismo-acoustic effect does not depend on position of the sub-ionospheric point within or outside the Dobrovolsky circle.

As for the sub-ionospheric point of the second hop, an effect from penetration into the ionosphere of the acoustic waves originated from vertical movement of the earth's surface by the passage of the Rayleigh wave was registered there too. We do not include these data into the article, since in the second point it was more complicated to select the seismo-ionospheric effect because of interferences which have appeared at that time. Possibly, we return to this question later using an additional operation method of the Doppler signal.

QUESTION #5 
In Figure 8, the authors have presented the Doppler shift of ionospheric signal in comparison with the seismogram taken at the KBL seismological station. The distance of the epicenter from the Kabul station is 2890 km, whereas the distance of the Trialeti station is only 785 km. Why it is coinciding with the station far from the epicenter? What type of anomalies are observed within the earthquake preparation zone?

++++ ANSWER:
In fact, most close to the sub-ionospheric point were the seismological stations TRLT in Trialeti, Georgia; MV06 in Guzdek, Azerbaijan; SIMI in Simiganj, Tajikistan; and KBL in Kabul, Afghanistan (see Table 1). Looking from the epicenter, the azimuth of the sub-ionospheric point was $A=100^\circ$.  The azimuth, relative to the epicenter, of the nearest to the sub-ionospheric point seismological stations TRLT and MV06 is, correspondingly, $49^\circ$ and $68^\circ$. The azimuth of the more distant seismological stations, SIMI,  $77^\circ$, and KBL, $86^\circ$, is closer to the direction $A=100^\circ$. The surface Rayleigh wave was propagating from the epicenter to the sub-ionospheric point of the first hop in the direction with $A=100^\circ$. For determination of the arrival moment of the surface seismic wave to the sub-ionospheric point the stations SIMI and KBL were selected as those which have the most close azimuth to the $A=100^\circ$ direction.

This explanation is placed in the text.

QUESTION #6
The Simiganj station which is also 2801 km away from the epicenter and receives the seismic wave almost at the same time as Kabul. The authors presented the
correlation coefficient in Table 2. The authors have also mentioned that it should not be expected any good coincidence between the waveforms of the Doppler frequency variation measured at a prolonged inclined radio pass and the seismic wave, since the sounding radio wave, travels considerable distance at its reflection in the ionosphere. What is the scenario within the preparation zone and at the nearest stations?

++++ ANSWER:
Indeed, the seismological stations SIMI and KBL are situated at an approximately same distance from the epicenter, and the correlation coefficients for these stations practically coincide (see Table 2). Even visually, it can be seen, that the seismogram waveforms registered at the stations SIMI and KBL are much similar to the variation of the Doppler frequency shift of ionospheric signal.

In the article, we made a correction, and the corresponding discussion fragment presently looks as the following:
"Such a close correlation of the first two wave packets confirms that the observed ionospheric disturbances were initiated by the passage of Rayleigh seismic waves. As the number of compared periods increases, the correlation coefficient drops down. Acoustic waves generated by a surface seismic wave affect vast areas of the ionosphere. The exact coincidence of the shapes of all DFS wave packets with a seismic wave should not be expected, since the radio path is inclined, and the probing radio wave, when reflected, travels a fairly long way in the ionosphere. The absence of correlation (r <0.25) was recorded at the points TRLT: Trialeti, Georgia and MV 06: Guzdek, Azerbaijan."

QUESTION #7
In Figure 10, authors have presented the variation of critical frequency f0F2 according to the ionosonde data, and before 8 days of the main shock, the maximum fluctuation of f0F2 was observed. But the overall variation of f0F2 increased from the observed values of 2021-2022 obtained from Nicosia station during seismically quiet years. How authors are distinguishing the anomaly for seismic activities if the overall value of the data increased? Just getting a fluctuation of 0.089 MHz and 0.315 MHz in the data is not that significant, the author should have calculated the anomaly of critical frequency variation from the quiet periods.

++++ ANSWERS:
> But the overall variation of f0F2 increased from the observed values of 2021-2022 obtained from Nicosia station during seismically quiet years. How authors are distinguishing the anomaly for seismic activities if the overall value of the data increased?

Indeed, because of the rise of solar activity, in 2023 it was observed an essential growth of the critical frequency f0F2, relative to 2021-2022. Correspondingly, the data for 2021-2022 are presented  only for illustration of the general variation trend of f0F2. Any detailed comparison of the 2021-2022 data with those for 2022-2023 is not the subject of the task connected with selection of the pre-seismic effect. In the current version of the Figure the plot of the 2021-2022 data was eliminated.

The essence of the pre-seismic effect selection was in comparison of the f0F2 variations registered by the ionosonde in Nicosia (Cyprus) and El Arenosillo (Spain) located, correspondingly, at the distances of 422km and 3887km form the epicenter. Also, it was taken into account, that both points are situated at close latitudes, and the Nicosia ionosonde falls into the Dobrovolsky circle, while the El Arenosillo occurs outside it.

> the author should have calculated the anomaly of critical frequency variation from the quiet periods.

It is seen in the plot, that during the seismically quite period between 1 December 2022 and 10 January 2023 the f0F2 variation measured at both considered ionosonde stations was small. Then, the dynamics of the critical frequency f0F2 has changed, and a most prominent effect was observed 8 days before the earthquake. The amplitude of the f0F2 change at the closer to the epicenter Nicosia station was 3.5 time higher than in El Arenosillo. This is why the prevailing lowering of the f0F2 frequency at Nicosia station, which had the minimum at 29 January, we suggest to consider as a pre-seismic response of the ionosphere to preparation of the earthquake.

> Just getting a fluctuation of 0.089 MHz and 0.315 MHz in the data is not that significant.

You are right, the values are small. This was the reason why, to reveal the effect, it was applied the daily averaging of the foF2 measurements data with subsequent smoothing by the running average filter over 20 points (i.e. days). Only with such intensive averaging it succeeded to reveal the prevailing reaction of the ionosphere in Nicosia point, though the absolute amplitudes of the decrease were only 0.089 and 0.315 MHz. 

QUESTION #8
In Figure 11, the authors presented the 4 points running average of the Doppler frequency shift. The maximum value of shift is observed after the main shock. Also, two preceding rises of the Doppler frequency are observed 8 and 3 days before the earthquake. The authors explained the entire shift as a result of the processes in the lithosphere within the area of earthquake preparation. What type of mechanism is observed and causing this enhancement is not clearly described. A clear explanation of the observed results is required.

++++ ANSWER:
The maximum value of the Doppler shift was observed after the main shock, in the period of the high aftershock activity. This question demands a separate discussion. In the article, we consider only the  effects which appeared before the main shock on 6 February 2023. As for a probable generation mechanism of pre-seismic ionospheric disturbances, we consider the concept of lithospheric-atmospheric-ionospheric coupling. The possible mechanisms of ionospheric anomalies are widely discussed in literature, where the connection between the lithosphere, atmosphere, and ionosphere  is treated in the frames of the Global Electric Circuit. The process of radon exhalation resulting in ionization of lower atmosphere is supposed to be one of the leading factors of the lithospheric-atmospheric-ionospheric coupling. In turn, the conductivity change of the atmosphere because of the ionization results in modification of the ionosphere through the medium of the atmospheric electric field. Such processes encompass considerable volume in the ionosphere above the region of earthquake preparation.

With account to your remark, the above explanation was added to the text of the article.

QUESTION #9
What is the novelty of this study in the aspect of the LAIC mechanism? The electromagnetic, acoustic, and thermal channels are well known in the LAIC mechanism and scientists are observing anomalous behavior of different parameters starting from the
1964 Great Alaskan earthquake. So many papers are published on case studies and multi-parametric approaches (Pulinets et al. 2016, De Santis et al. 2020) How this study is contributing in understanding the percolation of lithospheric anomalies into the ionospheric region?

++++ ANSWER:
The next summarizing paragraph was added to Conclusion section:

"With development of instruments and methods, new facts come to light on appearance of seismogenic disturbances in the various regions of the lithosphere, atmosphere, and ionosphere during the short-time period of earthquake preparation. New experimental data are necessary for further understanding the penetration of lithospheric disturbances into the ionosphere and of the mechanism of lithospheric-atmospheric-ionospheric coupling. Some advantages, from the view point of short-time earthquake forecast, belong to the ground-based investigation methods, one of which is the method of the Doppler ionosphere sounding with continuous emittance of the carrier radio wave. The method of Doppler measurements applied in this work not only permits to perform continuous monitoring of the ionosphere, but provides possibility to select the various radio paths in the direction of the sources of large earthquakes, and also to commit the measurements at large distance from earthquake sources. These advantages were realized in the present work, where it succeeded to detect the seismogenic effects in the ionosphere from the February 6, 2023 $M7.8$ earthquake in Turkey at a distance of about 3000\,km. It was confirmed the acoustic propagation mechanism of the disturbances from the lithosphere up to the ionosphere height, and, in agreement with the concept of lithospheric-atmospheric-ionospheric coupling, it was considered an appearance of pre-seismic disturbances in the ionosphere 8 and 3\,days before the main shock."

Reviewer 2 Report

The manuscript: Investigation of the pre-and co-seismic ionospheric effects from the February 6, 2023 M7.8 Turkey earthquake by a Doppler ionosonde, written by Nazyf Salikhov, Alexander Shepetov, Galina Pak, Serik Nurakynov, Azamat Kaldybayev, Vladimir Ryabov, and Valery Zhukov, reports observations which should be of interest for the scientific community and so should be sustained at my modest advice.

At the same time, however, such reports should satisfy a rigor level to be at the standard level for publication. In fact, some sentence is not demonstrated several themes should be discussed more extensively. Finally, Sun, geomagnetic, and meteorological activities are not analyzed in this manuscript, particularly on February 6. Please, respond to the following questions. In this case, an improvement in the English language is also necessary and I suggest using a native speaker to correct the entire manuscript.

Abstract

It is succinct and the kind of analysis is not described, Authors should better describe what they made and how they obtained the results.

Given the dimensions of the seismic source (and looking at English), the distances of 1591, 3010, 422, and 3887 km should be replaced by 1,500, 3,000, 400, and 3,800 km, respectively.

Introduction

Before the sentence of lines 18-20, please describe in deep the earthquake and the tectonic region where it occurred.

The English should be completely reviewed and more particulars added to the cited works.

Material and Methods

The sentence in lines 76-79 is too long and should be divided in two.

Lines 80-90, please describe the functioning principle, the parts of the system, and the method of analysis. Divide into more sentences, English should be revised.

Line 99, I don't understand how it is possible to consider such a precise distance when the dimensions of the fault itself is hundreds of km, please explain better. Same observation at lines 106 and 111.

There is no description of Figure 2 in the text. Please, describe how it was obtained and what it means.

Ionospheric effects of the earthquake

Lines 115-119 rewrite the sentences.

Lines 120-156 the English should be completely revised.

Line 147, Figure 4 alone is not a demonstration, please explain better.

Line 164, for the first time Authors speak about Figure 2, without describing it, and after Figures 3 and 4... Is it a true seismogenic disturbance? How to exclude that it was not an effect of the Sun and geomagnetic influence? The authors reported the possibility that Sun and geomagnetic activity are able to disturb the ionosphere in the Introduction. However, here they didn't describe the Sun and geomagnetic activities on February 6. Furthermore, also intense meteorological activity should be reported. Please describe in deep.

Line 165, please describe IRI2016.

Line 178, please describe IGRF12, why don't use the most recent IGRF13?

Lines 193-212, review the English.

Pre-seismic ionosphere effects

How to compare lines 1 and 2 with 3 of Figure 10? It seems not statistically significant to consider the same period of only one year.

Lines 272-273, please, report ap, kp, and Dst indexes.

Lines 293-296, there is no discussion of the statistical significance of this variation to affirm that it is an anomaly.

Affirmation at lines 298-299 is not demonstrated.

Lines 300-306, the discussion should be deeply extended.

Conclusions

Only points 1, 2, and 3 seem to be considerable after the Sun and geomagnetic activities report on February 6. Also, meteorological activity lacks to be described on February 6, 2023.

I suggest using a native speaker to correct the entire manuscript.

Author Response

QUESTION #1
Abstract
It is succinct and the kind of analysis is not described, Authors should better describe what they made and how they obtained the results.

++++ ANSWER: the abstract is enlarged, according to the recommendation.

QUESTION #2
Abstract
Given the dimensions of the seismic source (and looking at English), the distances of 1591, 3010, 422, and 3887 km should be replaced by 1,500, 3,000, 400, and 3,800 km, respectively.

++++ ANSWER: 
In the article, we define the distance to the sub-ionospheric point at the first hop of the radio path not from the source of the earthquake, but from the epicenter. This is why, for example, the value 1591km is the distance from the epicenter to the sub-ionospheric point. The epicenter has the strict geographic coordinates N37.23, E37.02, which was taken from the earthquakes catalog IRIS (www.iris.edu). The coordinates of the sub-ionospheric point, N33.543, E54.003, were determined by calculation of the trajectory of the sounding radio wave. Thus, the distances 1591, 3010, 422, and 3887km mentioned in the article were defined according to the geographic coordinates of corresponding points using the program Garmin MapSource, which provides the accuracy of distance determination about ~0.1km. In the article these values are rounded up to 1km.

QUESTION #3
Introduction
Before the sentence of lines 18-20, please describe in deep the earthquake and the tectonic region where it occurred.

++++ ANSWER: 
A description of the characteristics of the main earthquake shock, which had the magnitude M=7.8 and occurred at 01:17:34\,UTC on February~6, 2023, was added in the beginning of the Introduction section. As for the next powerful shock at 10:24:48\,UTC, it is not mentioned in the article, since at that time the radio receiver of the Doppler ionosonde has switched to other frequency according to its schedule, and was operating with the radio path ''Urumqi--Institute of Ionosphere  (Almaty)''

QUESTION #4
Introduction
The English should be completely reviewed and more particulars added to the cited works.

++++ ANSWER:
The Introduction section was reconsidered, and some details of the mentioned studies were added to it.

QUESTIONS #5 and #6
Material and Methods
The sentence in lines 76-79 is too long and should be divided in two.

Lines 80-90, please describe the functioning principle, the parts of the system, and the method of analysis. Divide into more sentences, English should be revised.

++++ ANSWER:
The text fragments are corrected with account to the remarks.

QUESTION #7
Line 99, I don't understand how it is possible to consider such a precise distance when the dimensions of the fault itself is hundreds of km, please explain better. Same observation at lines 106 and 111.

++++ ANSWER:
The explanation is given above in the answer to Question #2.

QUESTION #8
There is no description of Figure 2 in the text. Please, describe how it was obtained and what it means.

++++ ANSWER:
The reference to Figure 2 and the corresponding description were added to the text in the proper place. Much thanks for this correction.

QUESTIONS #9 and #10
Lines 115-119 rewrite the sentences.
Lines 120-156 the English should be completely revised.

++++ ANSWER:
The mentioned fragments in the text were rewritten.

QUESTION #11
Line 147, Figure 4 alone is not a demonstration, please explain better.

++++ ANSWER:
We agree that the sentence "From the time diagram of Figure 6 it is evident, that the ionospheric disturbances were caused by the acoustic waves originating from the vertical movement of the earth's surface by propagation of the Rayleigh wave" is premature, indeed, in this place, since the calculation of the propagation of acoustic wave is made later in the text. Presently this phrase is removed.

QUESTION #12
Line 164, for the first time Authors speak about Figure 2, without describing it, and after Figures 3 and 4... Is it a true seismogenic disturbance? How to exclude that it was not an effect of the Sun and geomagnetic influence? The authors reported the possibility that Sun and geomagnetic activity are able to disturb the ionosphere in the Introduction. However, here they didn't describe the Sun and geomagnetic activities on February 6. Furthermore, also intense meteorological activity should be reported. Please describe in deep.

++++ ANSWER:
As mentioned above, the fault with the reference to Figure 2 is presently corrected.

To answer the question on reality of the discussed seismogenic disturbance in the ionosphere and possibility of its imitation by the processes of solar or geomagnetic activity, a paragraph 'Geomagnetic conditions' with proper discussion was added into Section 2 'Material and methods'.

QUESTION #13
Line 165, please describe IRI2016.

++++ ANSWER:
The sentence "The international etalon model of the ionosphere IRI2016, together with the set of coefficients IGRF13, permits to deduce various parameters of the ionosphere for specific combination of the geographical location, date, and time." was added to the text.

QUESTION #14
Line 178, please describe IGRF12, why don't use the most recent IGRF13?

++++ ANSWER:
There was a mistake in the text with the erroneous 'IGRF12' designation. Actually, we use the IGRF13 model everywhere. Thanks for the correction.

QUESTION #15
Lines 193-212, review the English.

++++ ANSWER:
The text fragment was corrected.

QUESTION #16
How to compare lines 1 and 2 with 3 of Figure 10? It seems not statistically significant to consider the same period of only one year.

++++ ANSWER:
The f0F2 frequencies for the previous 2022 year in this figure are plotted only for comparison with the current 2023 data. It was not supposed to present any statistical data for many years.

QUESTION #17
Lines 272-273, please, report ap, kp, and Dst indexes.

++++ ANSWER:
These data are presented in the new paragraph 'Geomagnetic conditions' in Section 2.

QUESTION #18
Lines 293-296, there is no discussion of the statistical significance of this variation to affirm that it is an anomaly.

++++ ANSWER:
The limits of the confidence interval were implicitly plotted in Figure 12, and also some explanation of statistical aspects was added to the main text.

QUESTION #19 (20)
Affirmation at lines 298-299 is not demonstrated.

++++ ANSWER:
This sentence was changed to a more conservative sentence:

It should be noted a remarkable coincidence in the time, of approximately 8~days before the earthquake, in appearance of pre-seismic anomalous effects among variations of both the critical frequency f0F2, and of the Doppler frequency shift of ionospheric signal in the limits of Dobrovolsky radius...

QUESTION #20 (21)
Lines 300-306, the discussion should be deeply extended.

++++ ANSWER:
The discussion of the results presented in the article was enlarged by a review of more literature sources.

QUESTION #21 (22)
Only points 1, 2, and 3 seem to be considerable after the Sun and geomagnetic activities report on February 6. Also, meteorological activity lacks to be described on February 6, 2023.

++++ ANSWER:
The statements of the points 4-6 were clarified. The geomagnetic conditions in the period of the earthquake  are considered in the paragraph added to Section 2.

Reviewer 3 Report

See the attached PDF entitled revision.pdf file 

Comments for author File: Comments.pdf

Author Response

QUESTION #1
Can we expect differences between anomalies related to one large earthquake instead of two or more large earthquake close in space?

++++ ANSWER:
By the earthquake in Turkey there were two main shocks with the magnitudes of M7.8 and M7.5, and with close epicenters within the Dobrovolsky circle. Presently by our means we can not select the pre-seismic response to each separate shock.

QUESTION #2
Have you correlated the ionospheric anomalies with the surface deformation due to the earthquakes? See figure below this question.

++++ ANSWER: 
We did not intend to do such correlation in the present work, but this is undoubtedly an interesting proposal for future development of the methods for reveling earthquake precursors.

QUESTION #2b
How do you explain the ionospheric anomaly related to aseismic anisotropy surface deformation. Note that south land of the East Anatolian Fault goes down almost 4 m along 350 km of fault plane and 25 km wide.

++++ ANSWER: 
In explaining the appearance of ionospheric anomalies before earthquake we rely on the concept of lithospheric-atmospheric-ionospheric coupling which remains under active development during last 50 years. According to this concept, one of the basic initialization factors is the exhalation of radioactive gases, such as radon and the products of its decay, because of the changes in the stressed-deformed state of the earth's crust in the period of earthquake preparation. This process results in anomalous ionization in the lower atmosphere, with subsequent change of the conductivity of the atmosphere. In turn, the conductivity change leads to modification of the ionosphere through the medium of the atmospheric electric field. Such processes encompass considerable volume in the ionosphere above the region of earthquake preparation. Realization of the mechanism of lithospheric-atmospheric-ionospheric coupling was demonstrated in our publication [11].

QUESTION #3
In fact, the maximum slip along the fault plane from the slip modelling of the USGS was estimated in 11 meters, approximately. The estimated depth of the earthquake was between 7 and 10 km. This parameter is quite important to stimulate neighbours active faults by changing the Coulomb static stress and charging these secondary faults. For the Turkiye sequence, the
modelling carried out by the USGS is the following:

What I am trying to explain is that earthquakes are not points in a map. Earthquakes are complex fault movements along km-sized fault planes which generates seismic acoustic waves in a huge wave front. If you put the Dobrovolsky radius of 2,259 km from the official epicenter, you are missing the 350 km of oriented rupture NE-SW as you can see in the macroseismic map intensity (shake map) of the Mw 7.8 main shock (source USGS https://earthquake.usgs.gov/earthquakes/eventpage/us6000jllz/shakemap/intensity)

++++ ANSWER:
Unfortunately, in present time it seems impossible to select the radio broadcast stations, which are  necessary for sounding the ionosphere along the additional radio paths by the method used.

QUESTION #4
Can you correlate the disturbance with the estimated ground deformation from INSAR data?

++++ ANSWER:
This is an interesting but very difficult task, which is not yet considered as a target of our investigations.

QUESTION #5
The only problem that I observe in the use of the Doppler anomaly as a seismic precursor is how to establish the epicenter and foresee the fault which is near the rupture to trigger a large earthquake. If you make an inverse Dobrovolsky radius from the anomaly point, you first need to know the magnitude of the earthquake. Then, you have to fit the master fault in a 360o circle and estimate the depth of the earthquake for modeling the shake map and the potential losses. I suppose that this is another stage of this work.

++++ ANSWER:
You are right, the nest step of the work can be developing in that direction. But, as it is said above, presently it is impossible to select the additional radio paths necessary for Doppler measurements in any arbitrary way.

QUESTION #6
Detected anomalies, 8 and 3 days before the main shock, almost one week Have you any idea about why 8 and 3 days?

++++ ANSWER:
This is again a very difficult question. Supposedly, it is connected with many parameters of an earthquake source, such as  stress deformation characteristics, the properties of the rocks, etc. Emergence of seismo-ionospheric anomalies 3-16 days before the large earthquakes was reported in many studies, such as [24-28,55], which were using the different methods for their measurement.

Reviewer 4 Report

The manuscript shows that acoustic waves can be triggered by Rayleigh waves and propagate upwards, causing changes in the records of the Doppler sounder. The manuscript is quite interesting. However, there are some scientific problems that need to be addressed before it can be published.

 

The seismic stations and ionosodes used in this study should be indicated in Figure 1.

 

What types of seismic data were used in this study? The authors compare the Doppler data with the seismic data and find high correlation coefficient values. The authors need to explain whether the high correlation coefficient values are attributed to displacement, velocity, or acceleration seismic data. Additionally, the authors should explain why these high correlation coefficient values are specifically associated with a particular seismic data.

 

If the displacement data used in this study are not available, the authors may need to recalculate the propagation time from the epicenter to the sub-ionosphere point at the surface and from the surface to the sub-ionosphere point above the surface.

 

Since the shifts in Doppler frequency are considered to be primarily caused by acoustic waves triggered by Rayleigh waves, the radius of the Dobrovolsky circle should be unrelated to the shifts in Doppler frequency.

 

It should be noted that two sub-ionospheric points can be identified. The authors have suggested that the shifts are related to Rayleigh waves, so why do they only present data from the first sub-ionospheric point and not the second one?

 

The closest station to the first sub-ionospheric point is MV06. Why did the authors not use seismic data from MV06, but instead use data from the KBL station?

 

Please explain the reasons for choosing the SIMI and KBL stations instead of the two stations near the sub-ionospheric point.

 

How do you know that the signals are not from the second sub-ionospheric point, but rather from the first one?

 

Was a filter used to process the data shown in Figure 8?

 

Pre-seismic ionospheric effects are not convincing. Significant differences are often observed between Line 1 and Line 2 in Figure 10. Since there is a certain distance between these two stations, differences between them would be normal. Additionally, it is confusing to compare the changes in Line 1 and Line 2 with Line 3 in Figure 10, as the changes at different times should also be different.

 

Could you provide an extension of the data in Figure 11? How was the determination made to use a 4-point running average as a filter?

non

Author Response

QUESTION #1
The seismic stations and ionosodes used in this study should be indicated in Figure1.

++++ ANSWER:
The geographical location of all measurement sites mentioned in the article is presently marked in the map of Figure 1.

QUESTION #2
What types of seismic data were used in this study? The authors compare the Doppler data with the seismic data and find high correlation coefficient values. The authors need to explain whether the high correlation coefficient values are attributed to displacement, velocity, or acceleration seismic data. Additionally, the authors should explain why these high correlation coefficient values are specifically associated with a particular seismic data.

++++ ANSWERS: 
> What types of seismic data were used in this study? 

The parameters of the earthquake and the seismograms were taken from the site "SAGE—Seismological Facility for the Advancement of Geoscience" of the IRIS consortium (https://ds.iris.edu), the ionograms of the Nicosia and El Arenosillo stations---from the site of the Global Ionosphere Radio Observatory (https://giro.uml.edu). The references to the all data sources used are placed in the text.

> The authors compare the Doppler data with the seismic data and find high correlation coefficient values. Additionally, the authors should explain why these high correlation coefficient values are specifically associated with a particular seismic data.

The high correlation coefficients, $r\ge 0.9$,  between the ionospheric and seismic measurements were mentioned as well in the publications cited in the text as [50] and [51]. These observations were confirmed by the model calculation [51].

> The authors need to explain whether the high correlation coefficient values are attributed to displacement, velocity, or acceleration seismic data.

By calculation of the correlation coefficient the variation of the Doppler signal, measured in Hz, was compared with the velocity of the ground movement by the passage of the Rayleigh wave. The raw data taken from the SAGE database, are expressed in 'counts', i.e. in the units of the analog-to-digital converter used by the measurements. The velocity of the ground expressed in m/s can be obtained by division of 'counts' to a calibration coefficient 3.27508e9 (https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data). For convenience of comparison, on the plots of Figures 6, 9, and 10 the data on the ground velocity were additionally normalized and expressed as 'signal amplitude' in arbitrary units.

QUESTION #3
If the displacement data used in this study are not available, the authors may need to recalculate the propagation time from the epicenter to the sub-ionosphere point at the surface and from the surface to the sub-ionosphere point above the surface.

++++ ANSWER: 
One of the tasks of the considered study was determination of the arrival moment of the seismic Rayleigh wave to the sub-ionospheric point. It was quite sufficient for this purpose to use seismograms taken from the SAGE site (https://ds.iris.edu)

QUESTION #4
Since the shifts in Doppler frequency are considered to be primarily caused by acoustic waves triggered by Rayleigh waves, the radius of the Dobrovolsky circle should be unrelated to the shifts in Doppler frequency.

++++ ANSWER:
Yes, you are right. The Doppler frequency shift is caused by penetration of the acoustic waves generated by the Rayleigh wave, and there is no connection with the Dobrovolsky radius in this process. We have corrected the inaccuracy of the sentence in the text.

QUESTION #5 
It should be noted that two sub-ionospheric points can be identified. The authors have suggested that the shifts are related to Rayleigh waves, so why do they only present data from the first sub-ionospheric point and not the second one?

++++ ANSWER:
In the sub-ionospheric point of the second hop it was also registered an effect from penetration into the ionosphere of the acoustic waves by the passage of the surface Rayleigh wave. We do not present these data in the article, since it is more complicated task to identify the effect in the second sub-ionospheric point because of the interferences which had appeared at that time. Possibly, we return to this question later using an additional operation method of the Doppler signal.

QUESTION #6
The closest station to the first sub-ionospheric point is MV06. Why did the authors not use seismic data from MV06, but instead use data from the KBL station?

++++ ANSWER:
In fact, most close to the sub-ionospheric point were the seismological stations TRLT in Trialeti, Georgia; MV06 in Guzdek, Azerbaijan; SIMI in Simiganj, Tajikistan; and KBL in Kabul, Afghanistan (see Table 1). Looking from the epicenter, the azimuth of the sub-ionospheric point was $A=100^\circ$.  The azimuth, relative to the epicenter, of the nearest to the sub-ionospheric point seismological stations TRLT and MV06 is, correspondingly, $49^\circ$ and $68^\circ$. The azimuth of the more distant seismological stations, SIMI,  $77^\circ$, and KBL, $86^\circ$, is closer to the direction $A=100^\circ$. The surface Rayleigh wave was propagating from the epicenter to the sub-ionospheric point of the first hop in the direction with $A=100^\circ$. For determination of the arrival moment of the surface seismic wave to the sub-ionospheric point the stations SIMI and KBL were selected as those which have the most close azimuth to the $A=100^\circ$ direction.

This explanation is placed in the text.

QUESTION #7
Please explain the reasons for choosing the SIMI and KBL stations instead of the two stations near the sub-ionospheric point.

++++ ANSWER:
The main criterion by selection of the SIMI and KBL points was the direction (azimuth) of the Rayleigh wave propagation from the epicenter to the sub-ionospheric point. The SIMI and KBL stations are most acceptable for the condition of azimuth closeness. 

QUESTION #8
How do you know that the signals are not from the second sub-ionospheric point, but rather from the first one?

++++ ANSWER:
Knowing the moment of the Rayleigh wave arrival in the first sub-ionospheric point and the appearance time of the ionospheric disturbance, we can estimate the time, in which the acoustic wave could reach the reflection point of the sounding radio wave (see Figures 7 and 8). The distance to the second sub-ionospheric point is essentially larger (see Figure 5), so the disturbance in the ionosphere should appear much later, which does not agree with the experimental data.

QUESTION #9
Was a filter used to process the data shown in Figure 8?

++++ ANSWER:
The time series of seismic data shown there is not filtered, and the variation of the Doppler shift signal was filtered by the 10-points running average filter. 

This explanation was added in the text.

QUESTION #10
Pre-seismic ionospheric effects are not convincing. Significant differences are often observed between Line 1 and Line 2 in Figure 10. Since there is a certain distance between these two stations, differences between them would be normal. Additionally, it is confusing to compare the changes in Line 1 and Line 2 with Line 3 in Figure 10, as the changes at different times should also be different.

++++ ANSWER:
With account of your remark, we decided to eliminate the line '3' (the plot of the 2021-2022 data) from the current version of Figure 10 (presently, it is Figure 11). Earlier, this plot was shown there for comparison: it was supposed, that if any response to the earthquake is absent, the variation records of the critical frequency f0F2 in both ionosonde stations would be nearly similar.

It should be stressed, that we operate with the records of the daily averaged f0F2 values. When the significant, of 3.5 times, difference was revealed between the f0F2 amplitudes at the near (422km) and far (3887km) ionosonde stations, we supposed that this effect can be considered as a pre-seismic disturbance in the ionosphere. Moreover, the appearance of the effect in the variation of critical frequency 8 days before the main shock coincided in time with the anomaly in the records of the Doppler frequency shift (see Figure 12).

QUESTION #11
Could you provide an extension of the data in Figure 11? How was the determination made to use a 4-point running average as a filter?

++++ ANSWER:
It was a magnetic storm observed on 15-16 January 2023, this is why the data in Figure 11 (presently, Figure 12) are presented starting since 18 January.

By filtration, we tried to apply a number of filters with the different kernel length; the 4 points running average filter was chosen as an optimal one.

Round 2

Reviewer 1 Report

The authors have addressed inquiries raised and incorporated points and citations in the paper. Furthermore, they have revised the introduction, the discussion and the conclusion part by adding a few sentences that have enhanced the manuscript. They have explained the possible mechanisms of ionospheric anomalies in the frames of the Global Electric Circuit. The process of radon exhalation resulting in ionization of lower atmosphere is supposed to be one of the leading factors of the lithospheric-atmospheric-ionospheric coupling. In turn, the conductivity change of the atmosphere because of the ionization results in modification of the ionosphere through the medium of the atmospheric electric field. I still have few questions related to the entire mechanism:

1) How cluster hydration is impacting the local electric fields?
2) What is the observational evidence of the lower atmospheric electric field to validate the claim? The authors should provide further clarification regarding the tropospheric ionization processes that result in the intrinsic electric field causing a potential difference within the lower atmosphere.

3) The authors have found anomalies one week before the mainshock. Previously, several authors found perturbations related to the electromagnetic channel and generation of anomalous electric fields few hours before the mainshock of the earthquakes from ground and satellite based observations. Can the authors shed light on that for this particular case?

Author Response

The authors have addressed inquiries raised and incorporated points and citations in the paper. Furthermore, they have revised the introduction, the discussion and the conclusion part by adding a few sentences that have enhanced the manuscript. They have explained the possible mechanisms of ionospheric anomalies in the frames of the Global Electric Circuit. The process of radon exhalation resulting in ionization of lower atmosphere is supposed to be one of the leading factors of the lithospheric-atmospheric-ionospheric coupling. In turn, the conductivity change of the atmosphere because of the ionization results in modification of the ionosphere through the medium of the atmospheric electric field. I still have few questions related to the entire mechanism:

1) How cluster hydration is impacting the local electric fields?

++++ ANSWER:
The sequence of lithospheric-atmospheric-ionospheric coupling supposes that after ionization of the air caused by the alpha-particles from radon decay there proceeds formation of clustered ions in the atmosphere. With this process it is connected changing of the conductivity of the atmosphere border layer and of the atmosphere electricity, which facilitates the generation of anomalous electric fields in the ionosphere. These mechanisms are discussed in the literature during more than half a century.

2) What is the observational evidence of the lower atmospheric electric field to validate the claim? The authors should provide further clarification regarding the tropospheric ionization processes that result in the intrinsic electric field causing a potential difference within the lower atmosphere.

++++ ANSWER:
Electric measurements within the Dobrovolsky circle were not planned in our work, so there are absent here any observations of the changes of atmospheric electric field, which could reinforce, indeed, interpretation of the anomalous effects detected in the ionosphere during the preparation period of the Turkey earthquake. Undoubtedly, thorough consideration of the ionization process in the troposphere is a separate very interesting problem, which is widely discussed in modern scientific literature. This is why we supposed it sufficient to give some references to the concept of lithospheric-atmospheric-ionospheric coupling, where these questions are discussed in detail.

3) The authors have found anomalies one week before the mainshock. Previously, several authors found perturbations related to the electromagnetic channel and generation of anomalous electric fields few hours before the mainshock of the earthquakes from ground and satellite based observations. Can the authors shed light on that for this particular case?

++++ ANSWER:
In fact, it is a very interesting result which confirms experimentally both the concept of lithospheric-atmospheric-ionospheric coupling and the possibility to register the seismogenic disturbances before a earthquake. We have also detected, though by other methods, the ionospheric anomalies 8 days before the earthquake in Turkey.

Reviewer 2 Report

The manuscript titled "Investigation of the pre-and co-seismic ionospheric effects from the February 6, 2023 M7.8 Turkey earthquake by a Doppler ionosonde" by Nazyf Salikhov, Alexander Shepetov, Galina Pak, Serik Nurakynov, Azamat Kaldybayev, Vladimir Ryabov, and Valery Zhukov has been significantly improved with respect to the previous version. I'm always convinced that this kind of study regarding earthquake-associated phenomena would be sustained. However, the manuscript is at my modest advice still not at the standard level for publication in a scientific journal. The motivations are that: 1) Authors lasted some strong sentences about their results without lasting a possibility of doubt; 2) the level of fluctuations cannot be deduced in an implicit way from a picture, they must be calculated. Being so, I strongly suggest to solve the following points: Abstract Lines 6-7: rewrite the sentence introducing the possibility of doubt ",which suggested... "; Lines 9-12: rewrite the sentence introducing the possibility of doubt... I do not agree with the chosen number of digits for distances because the earthquake epicenter is not identificable with such precision. Introduction A geological description of the area should be included. Dip, Rake, Strike, and quake duration are not included as well as fault dimensions. The tectonics of the region is not described. Materials Put the true dimensions of the earthquake fault and points for stations in Figure 1, and put the coordinates along the borders. The earthquake time is not well positioned with respect to the geomagnetic indexes in Figure 2, delimit 00:00:00 of every day with vertical grey lines. One or more references that defines the threshold under which the geomagnetic activity does not influence the ionosphere should be introduced. Ionospheric Effects of the EQ The background level is not calculated and it cannot be deduced by seeing a picture. A distribution of the fluctuations in a sufficiently long period of observation would be fitted and, after discovering what is the type of distribution, the correct number of sigmas should be deduced to obtain a low probability that the fluctuation is not due to chance. 2 sigmas are referred to a Gaussian distribution but in this manuscript is not demonstrated that the distribution of the fluctuations is a Gaussian. Lines 324-329 in the Conclusions. IRI2016 was not described in the Materials. In lines 353-354, you must motivate with a discussion and references. It is not true for me. Lines 362-364 "The difference in the amplitudes" should be compared with a set of observations to affirm that "gives a ground to suppose...". Lines 394-397 "±2sigmas" have no sense if a distribution of the fluctuations is not studied. It seems to me that a period of 12 days is too short for a statistical calculus. Consequently, the sentence in lines 397-401 is not correct. Please, delete lines 430-432, are pathetic. Conclusions must be completely rewritten. In particular, points 4-6 strongly changed.  

A native English speaker should correct the entire manuscript

Author Response

The manuscript titled "Investigation of the pre-and co-seismic ionospheric effects from the February 6, 2023 M7.8 Turkey earthquake by a Doppler ionosonde" by Nazyf Salikhov, Alexander Shepetov, Galina Pak, Serik Nurakynov, Azamat Kaldybayev, Vladimir Ryabov, and Valery Zhukov has been significantly improved with respect to the previous version. I'm always convinced that this kind of study regarding earthquake-associated phenomena would be sustained.

However, the manuscript is at my modest advice still not at the standard level for publication in a scientific journal. The motivations are that: 1) Authors lasted some strong sentences about their results without lasting a possibility of doubt; 2) the level of fluctuations cannot be deduced in an implicit way from a picture, they must be calculated.

Being so, I strongly suggest to solve the following points:

Abstract
Lines 6-7: rewrite the sentence introducing the possibility of doubt ",which suggested... ";

Lines 9-12: rewrite the sentence introducing the possibility of doubt...

I do not agree with the chosen number of digits for distances because the earthquake epicenter is not identificable with such precision.

++++ ANSWER:
The abstract was rewritten and presently it looks as the next:

During the catastrophic M7.8 earthquake in Turkey on February 6, 2023, the anomalous effects were revealed in the ionosphere, which are connected with various propagation mechanisms of seismogenic disturbance from the lithosphere up to the heights of the ionosphere. 17 minutes after the main shock, a co-seismic disturbance was detected by a Doppler ionosonde operating on an inclined, 3010 km long, two-hop radio path “Kuwait—Institute of Ionosphere (Almaty)”. An appearance of acoustic waves at the height of 232 km in the ionosphere was fixed 568 s after arrival of the surface Rayleigh wave to the sub-ionospheric point, and such delay agrees with the calculated propagation time of a vertically moving acoustic wave. The disturbance lasted 160 s, and its double amplitude was above 2 Hz, which noticeably exceeds the background fluctuation of Doppler frequency. Best coincidence between the records of the Doppler signal and of the surface seismic wave was observed over duration of the two leading waveform periods, with correlation coefficients 0.86 and 0.79 correspondingly. Pre-seismic effects in the ionosphere were revealed 8 days before the main shock both in the variations of the Doppler frequency and of the critical frequency f0F2. The probable origination mechanism of the pre-seismic ionospheric anomalies within the limits of Dobrovolsky radius may be considered in accordance with the concept of lithospheric-atmospheric-ionospheric coupling.

 

Introduction
A geological description of the area should be included. Dip, Rake, Strike, and quake duration are not included as well as fault dimensions. The tectonics of the region is not described.

++++ ANSWER:
Main properties of the earthquake, including its magnitude, geographical coordinates, the tectonic region, etc are presently provided in Introduction.

The goals of our work did not anticipate any investigation of the relationship between the parameters of the earthquake and appearance of ionospheric disturbance, though this is a separate interesting question. Nevertheless, we have such data:
date/time    2023-02-06 01:17:35
magnitude, Mw      7.8
seismic moment, Nm 5.39e20
latitude, deg.     37.17N
longitude, deg.    37.04E
depth, km          10
strike, deg.       318 228
dip, deg.          89 89
rake, deg.         -179 -1

It was important for us, that the first sub-ionospheric point at the radio path used by Doppler sounding, as well as the ionosonde at Cyprus island fall into the Dobrovolsky circle which limits the area of deformations in the lithosphere by earthquake preparation (Dobrovolsky, I. P.; Zubkov, S. I.; Miachkin, V. I. Estimation of the size of earthquake preparation zones. Pure and Applied Geophysics 1979, 117, 1025–1044. https://doi.org/10.1007/BF00876083). This circumstance permits to consider, with some degree of confidence, the anomalies revealed in the ionosphere as the effects connected with the preparation process of the earthquake. In our consideration we proceed from the concept of lithospheric-atmospheric-ionospheric coupling, which is widely discussed in modern scientific literature.

 

Materials
Put the true dimensions of the earthquake fault and points for stations in Figure 1, and put the coordinates along the borders.

++++ ANSWER:
Any precise geological particulars seem to be excessive for interpretation of the results acquired in present study. The only information necessary for calculation of the arrival time of acoustic wave into the reflection point of the sounding radio wave, of the velocity profiles, etc are the geographical coordinates of the earthquake epicenter and of the sub-ionospheric point at the first hop of the radio path, as well as the magnitude of the earthquake and the corresponding Dobrovolsky radius. True size of the earthquake source and location of its borders are not essential for the task considered in the article.

We took into account your remark concerning Figure 1 and made corresponding correction of the chart presented there.

 

2.2. Geomagnetic conditions
The earthquake time is not well positioned with respect to the geomagnetic indexes in Figure 2, delimit 00:00:00 of every day with vertical gray lines.

++++ ANSWER:
The plots of geomagnetic indices were modified according to your remark.

One or more references that defines the threshold under which the geomagnetic activity does not influence the ionosphere should be introduced.

++++ ANSWER:
The references [43-45] were added in Section 2.2, as well as discussion of the relevant threshold conditions of a geomagnetically quite environment.

 

Ionospheric Effects of the EQ
The background level is not calculated and it cannot be deduced by seeing a picture. A distribution of the fluctuations in a sufficiently long period of observation would be fitted and, after discovering what is the type of distribution, the correct number of sigmas should be deduced to obtain a low probability that the fluctuation is not due to chance.

2 sigmas are referred to a Gaussian distribution but in this manuscript is not demonstrated that the distribution of the fluctuations is a Gaussian.

++++ ANSWER:
With account of your remark, we changed the method to estimate the significance of the difference between the  time series of the data measured on 17-29 January (the background data set) and between 29 January and the date of the earthquake on 6 February. For the purpose, the mean values and standard deviations were defined for each data set. Then, based on a calculated Student criterion t=5.61, it was obtained the confidence level of the difference between the two time series p<0.001 (p=0.000026), which means that the difference is statistically significant. The calculations were made using the Excel program.

Lines 324-329 in the Conclusions. IRI2016 was not described in the Materials.

++++ ANSWER:
Since the International Reference Ionosphere model (IRI) is an international project sponsored by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI), we did not provide any detailed description of this model but contented with a reference to the official site [47] (https://ccms.gsfc.nasa.gov). The calculation of the electron concentration in the ionosphere Ne was made immediately at this site.

 

In lines 353-354, you must motivate with a discussion and references. It is not true for me.

++++ ANSWER:
Thanks for your remark, it was our mistake which is presently corrected. We intended to say that the geomagnetic environment remained quite since 17~January until 14~February, and any geomagnetic storms were absent in that time.

Lines 362-364 "The difference in the amplitudes" should be compared with a set of observations to affirm that "gives a ground to suppose...".

++++ ANSWER:
You are right, it is prematurely to make resolute conclusion on seismogenic origin of the drop in f0F2 frequency with a minimum on 29 January 2023. We changed this sentence to a more cautious supposition.

In the article we compare the data of the two ionosonde stations located at different distances from the earthquake epicenter: the station in Nicosia is situated at a distance of 420\,km, within the limits of the Dobrovolsky circle, while the El~Arenosillo one is at a much larger distance of $\sim$3880\,km, and outside the earthquake preparation zone defined by the Dobrovolsky radius. Nevertheless, a coincidence in the time was revealed between appearance of the anomalous pre-seismic effects detected in the ionosphere by the two independent methods, the Doppler and ionogram ones. These were the only anomalies which took place during the whole observable time interval before the Turkey earthquake, and under quiet geomagnetic conditions.

If another similar catastrophic events would happen, with some ionospheric stations falling inside the Dobrovolsky circle, it would be possible to draw more detailed comparative analysis. Nevertheless, the results presented in current study will not loose their actuality and can be a ground for further work.

 

Lines 394-397 "±2sigmas" have no sense if a distribution of the fluctuations is not studied. It seems to me that a period of 12 days is too short for a statistical calculus. Consequently, the sentence in lines 397-401 is not correct.

++++ ANSWER:
As explained above, presently the statistical significance of the difference in distributions is evaluated using the Student criterion.

 

Please, delete lines 430-432, are pathetic.

++++ ANSWER:
This phrase was more related with the direction of our experimental investigation and formerly published works, primarily [11], where the connection between the lithosphere and ionosphere was studied at preparation and in the time of earthquakes. Presently the sentence is rewritten in other variant.

 

Conclusions must be completely rewritten. In particular, points 4-6 strongly changed.

++++ ANSWER:
The content of the Conclusion section was considerably modified.

Reviewer 4 Report

I have carefully read the manuscript and the authors’ responses. They have made additions and substantial revisions to the manuscript. However, the revisions only partially address the comments raised. A significant scientific issue remains unresolved. Specifically, the authors should specify the types of seismic data (acceleration, velocity, and displacements) used in the manuscript. It is important to note that when converting seismic data from one type to another, the phase and shape of the waves can change, which could impact the results presented in the manuscript. Therefore, I recommend that the authors thoroughly examine the seismic data and provide comprehensive information in the manuscript.

Additionally, the authors should provide a valid justification for selecting a specific duration for constructing criteria, such as using the average plus two standard deviations. Different criteria may be obtained depending on the chosen duration. A short-duration dataset may also affect the accuracy of assessing pre-earthquake effects. Therefore, I suggest that the authors either reduce or remove the pre-earthquake effects from the manuscript.

non

Author Response

I have carefully read the manuscript and the authors’ responses. They have made additions and substantial revisions to the manuscript. However, the revisions only partially address the comments raised.

1. A significant scientific issue remains unresolved. Specifically, the authors should specify the types of seismic data (acceleration, velocity, and displacements) used in the manuscript.

++++ ANSWER:
An explanation concerning the seismological data presented was taken from the IRIS site (https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data) and copied into the text:

"In the Y-axis in the plot of Figure 6 are the values of analog-to–digital converter. The ground movement in units of m/s can be obtained by dividing 'count' by a calibration number equal to $3.27508\cdot 10^{9}$. On the graph, the seismic data 'count' is normalized into relative units for ease of viewing."

2. It is important to note that when converting seismic data from one type to another, the phase and shape of the waves can change, which could impact the results presented in the manuscript. Therefore, I recommend that the authors thoroughly examine the seismic data and provide comprehensive information in the manuscript.

++++ ANSWER:
Of course, both the shape and phase of a waveform can be changed by transformation of seismological data. But it was not the purpose of the article to study how the phase of a seismic wave influences its shape. By calculation of  correlation coefficients, only the shape of the Doppler frequency signal was compared against the shape of the seismogram of Z-component, which reflects the velocity of ground displacement by passage of the Rayleigh wave. Sufficiently high values of the correlation coefficients acquired by comparison of both waveforms confirm the conclusion on an acoustic origination mechanism of the detected ionospheric response.

3. Additionally, the authors should provide a valid justification for selecting a specific duration for constructing criteria, such as using the average plus two standard deviations. Different criteria may be obtained depending on the chosen duration. A short-duration dataset may also affect the accuracy of assessing pre-earthquake effects. Therefore, I suggest that the authors either reduce or remove the pre-earthquake effects from the manuscript.

++++ ANSWER:
You are right, limiting of dataset can influence the determination accuracy of the effects observed prior to the earthquake, and the correctness of conclusions depends on duration of the measurement time series: the longer the better. Unfortunately, we were rather restricted in selection of the time interval for searching for the ionospheric pre-seismic effects. On 15 and in the morning of 16 January 2023 it was observed a magnetic storm; this is why the interval between 17-29 January was chosen for an analysis of the background variation of the Doppler signal.

As discussed in the paragraph 2.2, the geomagnetic conditions remained relatively quiet between 17 January and the earthquake date 6 February (Кр<3, Dst<23nT, ap<18nT). This circumstance stipulated the selection of the interval for calculation of the mean and standard deviation parameters of the background variation of Doppler signal.

We hope that the said arguments permit to leave Figure 12 in the article, and to interpret as a probable response to the earthquake preparation the revealed rise of the Doppler shift frequency which took place since 29 January until 6 February.