Preseismic Groundwater Ion Content Variations: Observational Data in Flowing Wells of the Kamchatka Peninsula and Conceptual Model

Round 1

Reviewer 1 Report

The paper at first shows some variations in groundwater ions content observed in Kamchatka before the strongest earhquakes (Mw = 6.5 - 7.8) occurred in period 1986-1998. Then a model able to justify these anomalies is presented and applied to one of these earthquakes (1992, Mw=6.9). This application is the main new result reported in the paper; the anomalies and the model have been presented previously in other papers of the Authors and here are reported for showing in an  exhaustive way the background situation. Personally I agree with this setting. 

The experimental data are well reported and clearly presented. The model consider the cause of the variations in the ions content related to a mixing of waters with different chemical composition produced by the processes occurring during the preparatory phase of the forthcoming earthquake. In the paper it is shown as a such mixing can to give a good justification of the variations observed on the occasion of the 1992 earthquake.

Personally I think that the previous model is realistic and it is able to justify the preseismic variations in groundwater ions content but probably the variations observed in many cases in the groundwater gases content could be better justified with some influx of underground gases in the acquifer. This process could be indipendent by the previous mixing.

On the basis of the previous last statement I suggest that the title of the paper should be : "Preseismic groundwater ions content variations ....." and not "Hydrogeochemical earthquake precursors......" and this modification should be adopted also in the text. I am not a native english speaker but according to my opinion the language of the paper should be revised.

Author Response

1. I suggest that the title of the paper should be : "Preseismic groundwater ions content variations ....." and not "Hydrogeochemical earthquake precursors......" and this modification should be adopted also in the text. I am not a native english speaker but according to my opinion the language of the paper should be revised.

The title of the article has been changed to "Preseismic groundwater ion content variations: observational data in flowing wells of the Kamchatka Peninsula and conceptual model";

substantial editing of the text and captions has been performed.

2. “Personally I think that the previous model is realistic and it is able to justify the preseismic variations in groundwater ions content but probably the variations observed in many cases in the groundwater gases content could be better justified with some influx of underground gases in the aquifer. This process could be indipendent by the previous mixing.”

The issue of the relationship between anomalies in changes in the ionic composition of groundwater and the composition of free gas from the same well is important. At the same time, there is no model for such a relationship, primarily due to the small number of observational data for such a phenomenon. Therefore, we have given in the updated text an addition with the describing a single case of anomalous changes in the composition of free gas from well GK-1 before the earthquake on March 2, 1992 (lines 103-108).

Author Response File: Author Response.pdf

Reviewer 2 Report

The Authors present example of approach to describe earthquake precursors base on hydrogeochemical data. The aim of the work is worth because the authors have comprehensively and accurately summarized the current state of research. They also logically justified the relevance and topicality of the subject matter However, I have some suggestions that would allow some clarifications to be made:

1. In key words, authors should specify what type of modeling is meant.
2. The data used for the analysis and modeling seem to be outdated (1986-1998). Is it not possible to develop the subject of the article on the basis of current data? Certainly, this issue must be justified.
3. In lines 67-69 the analyzed chemical indicators should be precisely mentioned.
4. The information in lines 202-207 is well known to any person dealing with hydrogeochemistry. Nevertheless, they should be supported by biographies.
5. In point 3.3 (line 234) it is worth considering determining the correlation between the selected indicators. An example of such correlations can be found in other works about hydrogeochemistry proccesses controlling the formation of the chemical composition. Examples of such correlations can be found, for example, in these publications: https://doi.org/10.1007/s00484-020-01871-7 https://doi.org/10.3390/en13215584 https://doi.org/10.1016/j.apgeochem.2017.11.011 https://doi.org/10.1007/s11631-021-00481-3 https://doi.org/10.1016/j.scitotenv.2015.05.038 https://doi.org/10.1016/j.wsj.2017.05.002
6. In line 291 correct the numbering of the point
7. There are many self-citations in the bibliography, which is understandable and justified to present the history of research in this area. However, it would be worth referring to the study of similar cases in the world and the research of other scientists In my opinion, the manuscript could be accepted for the publication in the Minerals Journal after minor revision.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 2 Comments

1. «In key words, authors should specify what type of modeling is meant.»

In updated version of article, the term "modeling" has been removed from keywords.

2. “The data used for the analysis and modeling seem to be outdated (1986-1998). Is it not possible to develop the subject of the article on the basis of current data? Certainly, this issue must be justified.”

An explanation of the reasons for the change in well observation after 1998 has been added in the updated text (lines 68-73). Note also that anomalous changes in the chemical composition of water from a well before earthquakes are rare phenomena. At the same time, there is practically no data on such phenomena in wells operating under conditions of natural self-flowing, as the cases presented in the work.

3. In lines 67-69 the analyzed chemical indicators should be precisely mentioned.

Clarification is made on lines 66-67 of the updated version of the text «... concentration of anions Cl^-, HCO₃^-, SO₄^2-and cations Na⁺, K⁺, Ca²⁺, Mg²⁺…»

4. The information in lines 202-207 is well known to any person dealing with hydrogeochemistry. Nevertheless, they should be supported by biographies.

Reference No. 28 (line 209) to the manual on groundwater chemistry (Handbook of a hydrogeologist) was added to the References. The information in lines 197-209 is necessary in the further description of the model under consideration, especially for seismologists and geophysicists who also observe the groundwater chemical composition in wells.

5. In point 3.3 (line 234) it is worth considering determining the correlation between the selected indicators. An example of such correlations can be found in other works about hydrogeochemistry proccesses controlling the formation of the chemical composition.

Examples of such correlations can be found, for example, in these publications: https://doi.org/10.1007/s00484-020-01871-7 https://doi.org/10.3390/en13215584 https://doi.org/10.1016/j.apgeochem.2017.11.011 https://doi.org/10.1007/s11631-021-00481-3 https://doi.org/10.1016/j.scitotenv.2015.05.038 https://doi.org/10.1016/j.wsj.2017.05.002

We did not quite understand what kind of correlation is being discussed in the reviewer's question. Apparently, the reviewer had in mind line 334 in section 3.3 (?).

In addition, we express our gratitude for the references to the indicated highly professional works in the field of regional hydrogeochemistry. We also note that the features of the groundwater hydrogeochemistry in the wells under consideration, as well as of in other regime water vents of the Petropavlovsk-Kamchatsky polygon, are discussed in detail in publication No. 27 in References:

Kopylova, G.N. et al. The Chemical Composition of Ground Water in Observational Water Vents in the Petropavlovsk Geodynamic Test Site: The Classification and Effects of Large Earthquakes. Journal of Volcanology and Seismology 2018, 12, 268-286. https://doi.org/10.1134/S0742046318040048.

We believe that there is potential in the reviewer's commentary for further investigation of the hydrogeochemical anomaly in the water composition from well M-1 when constructing correlations between individual indicators of water composition over time. Since our work evaluates the state of the hydrogeochemical system at the extreme stage of the recorded anomaly before the earthquake.

6. In line 291 correct the numbering of the point

Thank you! Made a fix.

7. There are many self-citations in the bibliography, which is understandable and justified to present the history of research in this area. However, it would be worth referring to the study of similar cases in the world and the research of other scientists.

Unfortunately, we are not aware of any work on the registration of a complete set of macrocomponents in the water composition in self-flowing wells operating for a long time in undisturbed conditions, with an observation frequency of three days or less. The data on hydrogeochemical observations in other regions, cited in the introductory part (No. 4-13 in References), do not satisfy these conditions. Therefore, we are considering the prospects for searching for the effects of seismicity in changing the groundwater chemical composition with the automation of observations and the use of integral indicators of the chemical composition of water, such as the electrical conductivity of water.

Author Response File: Author Response.pdf