Response Analysis of Multi-Layered Volcanic Aquifers in Jeju Island to the 2011 M9.0 Tohoku-Oki Earthquake
, Kue-Young Kim 1, Kyoochul Ha 1, Jehyun Shin 1, Seho Hwang 1 and Soo-Hyoung Lee 1,*
Patrick Lachassagne
Round 1
Reviewer 1 Report
The paper reports the monitoring (hydraulic head, temperature, electrical conductivity) and interpretation of the impacts of seismic waves from the large M 9.0 2011 Japan earthquake observed in piezometers drilled in a coastal volcanic aquifer from Jeju island (South Korea).
The English language is of good quality. I only detected a few sentences that must be revised or typographical errors (see minor remarks below).
I think that this paper is worth to be published but only after a major revision as either the presentation of the results, or the interpretations, or both must be improved.
I found also several very minor issues in the paper that are listed as “minor remarks” and will need to be scrupulously addressed. However, they don’t fundamentally challenge the quality of the paper. The authors may provide a MSWord file with changes apparent in order that the associate editor checks.
Then, the quality of the paper must particularly be strengthened as regards:
1. better physically explaining and decomposing the various observed processes:
- wave transmission from the earthquake to the aquifer (observation wells). The fact that this is this kind of process that is really observed must also be a bit more discussed to convince the reader;
- better explain and justify the physical processes that explain piezometric changes, and their relative amplitudes from one piezometer to the other;
- and mainly (see below) the processes occurring in the obs. wells and explaining EC and T° profiles;
2. better interpreting the temperature and EC logs presented at Fig. 2. Interpreting T° and EC logs in unpumped wells is not straightforward as it must take into account possible vertical flow in the well that depend on the hydraulic head in each permeable level crosscut by the well (that may here be strongly influenced by density effects). Logs can also be influenced by previous pumpings performed in the well. Then, the interpretation proposed in section 4.2. is not detailed enough to be convincing.
A scrupulous demonstration should be provided, well by well, taking into account the knowledge about the location of pervious and impervious levels, what was done (pumping) in the wells previously, location of screen, etc.. If the authors did several logs, it may help. If they also did some logs while pumping, it may be much simpler to interpret. If possible, semi quantitative interpretations can be provided for mixings of water of various EC (ex.: upwards discharge Q1 with EC1 in the well below a Q2, EC2 water inflow from the aquifer to the well mixes and gives Q3 = Q1+Q2 and EC3 = Q1*EC1 + Q2*EC2). Additionally, the T° log may qualitatively help to check the performed hypotheses (mixings of cold and hot water, increase with depth with a gradient similar to geothermal may suggest no vertical flow in the well, and so on). The interpretation should begin either from the top or the bottom of the well, or both, as there are surely no flow area in the wells at the top and/or bottom if it faces on impervious zone.
For instance, at SS3, depending if the flow in the well is ascending or descending, one may interpret what happens at about 60 m either as an inflow of salter water or as an inflow of fresher water. The same at about 110 m, but in an opposite way. This is just an example.
Moreover, it should be explained when the logs were performed as they seem to be influenced by the tides. Comparison of logs performed at high and low tide may surely bring lots of additional information.
3. better interpreting and describing the changes observed after the earthquake.
Ex: p. 7, section 4.3, it must be said when these EC measurements where performed.
The deeper interpretation proposed in §2. Above, and knowledge is mandatory to be able to interpret the impact of tides, and also the impact of the earthquake.
4. Then, to my opinion, Figs. 10 a and b must be revised.
They must particularly show, if any, the vertical flow vectors within the wells, and the relationships with the aquifers (inflow or outflow), that should explain EC, mixings, and so on, and finally the EC (and T) profiles in the wells.
For instance, one cannot draw 2 arrows facing one each other (“Fresh Water” and “Saline water”). If there are only 2 aquifers, inflows or outflows to the well can only occur at the places the well crosses the aquifers.
This must be done for before and after the earthquake.
Minor remarks (numbers, and line numbers refer to the annotated manuscript):
- a detail for next submission: please number lines; it will ease the review
- p. 1, Introduction, paragraph 1, line 4: earthquakes not only provoke compression or expansion of aquifers (that are of course linked to their hydrodynamical parameters – line 7); they may also provoke changes of the hydrodynamic parameters, notably permeability (see for instance Lachassagne et al., 2011). Overall, the recent paper from Petitta et al. may also be cited.
- p. 2, Introduction, line 6: “in” is missing before “coastal”.
- p. 2, Introduction, line 8: “complex structure and hydro…”.
- p. 2, Table 1: it would be nice to also have a column with piezometric level in masl, and to explain that DTW and piezo are mean values. Well radius: indicate if drilling radius or tube radius
- p. 2, section 2.1., line 7, cite Fig 2 for location of probes.
- p. 2, section 2.1., line 11 and following, cite Fig 2, indicate exact location of Divers, as well as on figure 2. Indicate also the part of the well that is screened. Homogeneize text with figure: “transition zone” vs “mixing zone”. It would be nice to complete this section and fig 2 with a table summarizing all metrological parameters: location, type, measurement interval, etc..
- p. 3, section 2.2., line 1: “from bottom to top”.
- p. 3, section 2.2., lines 4, 5: please rewrite it is not clear: from pumping tests, from time series, specific capacity = Q/s? Diffusivity = T/S
- p. 3, section 2.2., line 7: indicate also which lithological facies are of low permeability.
- p. 3, section 2.2., line 9: “permissive” = “permeability”? You mean due to weathering? Please precise.
- p. 4, section 2.2., line 1: really neutron log, not gamma ray? Please check.
- p. 4, section 2.2., line 3: “mud” = “clay”? Please modify here if you agree, and elsewhere in the paper (same page line 6 for instance, Fig. 10).
- p. 4, section 2.2., line 3: “bio-clastic sediments”. OK? Please indicate these lower and upper limits on Fig. 2. Correspondence is not very clear. Again, harmonize between text and fig 2 (and others if necessary): for instance, clinker vs scoria.
Moreover, Fig. 2 should enable to provide info about (i) lithology and (ii) permeability (high/low for instance), for instance by drawing 2 logs for each obs. well. Moreover, small thickness lithologies cannot be identified. Revise legend (with colors?).
It would enable to better understand what is meant by “upper aquifer” and “lower aquifer” p. 8.
- p. 4, section 2.2., lines 5 & 6-7 (also in section 4.1.): I would not speak about “groundwater conduits” and “interrupt GW flow” but respectively as “aquifers” and “aquicludes/aquitards” or “low permeability layers”. Otherwise, define what is a “conduit”.
In this section 2, the uncertainty about the time measurements should be indicated: were all loggers times synchronized? Were the related to international time? With which relative and absolute precision?
- p. 4, section 3.1.: N = 2. Please indicate then the considered time span. I feel the average is not the same for all groundwater level probes (Divers and multidepth probes). Moreover, I fear an error, the filtering is much more than 5 data (fig. 3).
- p. 4, section 3.2., line 2: what is the “hydraulic diffusion coefficient” (T/S?)? A table with all parameters used in the paper, and their units should be provided.
- p. 4, equ. 2: there is a blanc within “Si n”.
- p. 4, section 3.2.: delay time: you may explain that there might be an ambiguity if it exceeds the wavelength. Right?
- p. 6, section 4.1., lines 5-6: you may cite the order of magnitude of the amplitude: about 50 cm at SS1, a few cm at SS3. Right?
- p. 6, section 4.1. (and others): use SI units (MKS): Transmissivity in m2/s.
- p. 6, section 4.1., second paragraph, lines 7-9: it is not clear how these results are reported in Table 3. It seems they are not.
Moreover, these results are not consistent with the T computation from hydraulic diffusivity. This apparent inconsistency must be discussed: surely as first method = local T, whereas second method encompass the whole aquifer between the sea and the well. Right? The fact that one considers the same S for both aquifers must also be discussed (S is much less varying that T).
- p. 7, section 4.1., first paragraph, first lines: I would rather intervert: The GW level changes are related to T, which is fixed, and not the opposite. Right? Same for lines 4 & 5; it suggests that the permeability is changing (linearly increasing).
More generally, the physical processes must be better explained.
- p. 8, Fig. 5: would it be possible to add a scale for tides?
- p. 8, line before the last one: flows vertically. Upwards or downwards?
- p. 10, line 2. Delete blank after EC.
- Fig. 10: there is a need of a legend for the colors.
Lachassagne, P., Léonardi, V., Vittecoq, B., Henriot, A., 2011 Interpretation of the piezometric fluctuations and precursors associated with the November 29, 2007, magnitude 7.4 earthquake in Martinique (Lesser Antilles) Comptes-Rendus Geosciences 343 (2011) 760–776
Petitta, M., Mastrorillo, L., Preziosi, E., Banzato, F., Barberio, M.D., Billi, A., Cambi, C., De Luca, G., Di Carlo, G., Di Curzio, D., Di Salvo, C., Nanni, T., Palpacelli, S., Rusi, S., Saroli, M., Tallini, M., Tazioli, A., Valigi, D., Vivalda, P., Doglion, C., 2018 Water-table and discharge changes associated with the 2016 –2017 seismic sequence in central Italy: hydrogeological data and a conceptual model for fractured carbonate aquifers Hydrogeology Journal (2018) 26:1009 – 1026 https://doi.org/10.1007/s10040-017-1717-7
Author Response
Response Letter
Date: March 06, 2019
To: Bojana Mijanovic
From: Soo-Hyoung Lee, [email protected]
Manuscript ID: water-451632
Title of the manuscript: Response Analysis of Multi-Layered volcanic aquifers in Jeju Island to the M 9.0 Tohoku-Oki Earthquake
Dear Bojana Mijanovic and Reviewer’s:
We are very pleased to submit the manuscript entitled ‘Response analysis of multi-layered volcaic aquifers in Jeju Island to the M 9.0 Tohoku-Oki Earthquake’ in Water. We fully reflected the advice of the Reviewer’s. Also, we received one more proceeding from MDPI English editing. The contents of the manuscript were revised, and the figures were revised and newly added. I state that the manuscript is original work. All the authors agree with the contents.
Enclosed are: the manuscript, 5 tables, and 11 figures.
(modified: 1 table, 3 figures / newly added: 1 figure)
The revised parts of the manuscript were indicated in blue color. Below, we stated our replies to the reviewer’s comments.
Review 1:
Dear Colleagues,
Nice paper, only some minor errors in text you should correct.
Best regards!
Reply: Thank you very much. We agree with your comments. Accordingly, manuscript is revised in order to reflect the reviewer’s comments.
Review 2:
I think that this paper is worth to be published but only after a major revision as either the presentation of the results, or the interpretations, or both must be improved. Then, the quality of the paper must particularly be strengthened as regards:
1. Better physically explaining and decomposing the various observed processes:
- wave transmission from the earthquake to the aquifer(observation wells). The fact that this is kind of process that is really observed must also be a bit more discussed to convince the reader; better explain and justify the physical processes that explain piezometric changes, and their relative amplitudes from one piezometer to the other;
Reply: We agree with your comments. We tried to make a better interpretation of this paper. The complemented paragraph was added to introduction. “Generally, when the seismic waves pass, the changes of pore pressure cause flow into and out of the well from aquifer by dynamic stress (seismic wave). The oscillatory changes in groundwater level occur when the aquifer has high enough transmissivity, permeability, etc.” Also, we mentioned results of the geophysical well loggings on result.
“Using a geophysical well logging system (2000 m length winch and Micro loggerⅡ produced by Robertson Geologging Co., United Kingdom), Natural gamma, neutron, vertical flowmeter, EC, and temperature logs were carried out at the speed of 3 m/min with a measuring interval of 1 cm. Fig. 5 is the results of those geophysical loggings in SS1 well before the M 9.0 Tohoku-Oki Earthquake [52]. The basalt formation until 135 m showed continuously both high and low porosity because the outside part of the basalt was cooled rapidly and the inside part of the basalt was cooled slowly. The neutron log showed those properties. The intervals with very high porosity between basalts are sedimentary formation. The formation below 135 m consists of the tuff with very high porosity relatively in SS1 well. Based on the natural gamma log, the basalt formation showed changeable values according to the components and the sedimentary environment when magma erupted. The tuff formation below 135 m showed high values of the natural gamma and the U formation below the tuff formation showed the highest values of the natural gamma. Based on the temperature logs, The temperature decreased from up to down until 60 m and the temperature below 60 m increased gradually as the geothermal gradient. Based on the EC logs, the EC increased dramatically at around 60 m caused by the effects of seawater intrusion until 80 m.”
2. Better interpreting the temperature and EC log presented at Fig. 2. Interpreting T and EC logs in unpumped wells is not straightforward as it must take into account possible vertical flow in the well that depend on the hydraulic head in each permeable level crosscut by the well. Logs can also be influenced by previous pumpings performed in the well. Then, the interpretation proposed in section 4.2. is not detailed enough to be convincing.
Reply: According to your comments, we revised section 2.2 and 4.2. Originally, we mentioned temperature and EC logs of SS-1, SS-2, and SS-3 on section 4.2. We moved contents of T and EC logs to section 2.2. for explaining Fig. 2. Also, we added results of well loggings (natural gamma, neutron, 1-D flowmeter, EC, Temperature log) acquired in SS-1 on section 4.2. for readers. Unfortunately, we could not acquire temperature and EC logs during the pumping test and we could not consider effects of the tide when performing geophysical loggings. But we made efforts to give a lot of information which we have about the borehole (SS1) to readers.
3. better interpreting and describing the changes observed after the earthquake.
Reply: Fig. 8 shows the changes of EC with data fore and after earthquake.
4. Then, to my opinion, Figs. 10 a and b must be revised.
Reply: According to your comments, we modified that the Fig. 11(before modified Fig. 10) a and b were revised.
5. Minor remarks
- a detail for next submission
- P.1, introduction, 1, line 4: earthquakes not only provoke compression or expansion of aquifers; they may also provoke changes of the hydrodynamic parameters, notable permeability. Overall, the recent paper from Petitta et al. may also be cited.
- Reply: We agree with your comments. Accordingly, we have modified and added a sentence.
- P.2, introduction, line 6: “in” is missing before “coastal”
- Reply: We agree with your comments. We corrected the word.
-
- P.2, introduction, line 8: “complex structure and hydro…”
- Reply: We agree with your comments. Accordingly, we revised the sentence.
-
- P.2, table 1: it would be nice to also have a column with piezometric level in masl. And to explain that DTW and piezo are mean values. Well radius: indeicate if drilling radius or tube radius
- Reply: We agree with your comments. Accordingly, we revised the table 1.
-
- p. 2, section 2.1., line 7, cite Fig 2 for location of probes.
- Reply: Fig. 2 is large-scale information of SS1-SS3. We have table 4 and Fig. 8 to give information of multi-depth probes in SS1 to readers.
-
- p. 2, section 2.1., line 11 and following, cite Fig 2, indicate exact location of Divers, as well as on figure 2. Indicate also the part of the well that is screened. Homogeneize text with figure: “transition zone” vs “mixing zone”. It would be nice to complete this section and fig 2 with a table summarizing all metrological parameters: location, type, measurement interval, etc..
- Reply: We agree with your comments. We indicated depth of screen on table 1. Two words are not different.
-
- - p. 3, section 2.2., line 1: “from bottom to top”.
- Reply: We agree with your comments. We added the expression.
-
- - p. 3, section 2.2., lines 4, 5: please rewrite it is not clear: from pumping tests, from time series, specific capacity = Q/s? Diffusivity = T/S
- . Reply: We agree with your comments. We modified the sentences and referred to previous study.
-
- - p. 3, section 2.2., line 7: indicate also which lithological facies are of low permeability.
- Reply: We agree with your comments. Accordingly, we mentioned low-permeability layers (U-formation and the Seogwipo formation).
-
- - p. 3, section 2.2., line 9: “permissive” = “permeability”? You mean due to weathering? Please precise.
- Reply: We agree with your comments. “permeability” is correct. We revised that word.
-
- - p. 4, section 2.2., line 1: really neutron log, not gamma ray? Please check.
- Reply: In section 4.2, we added contents about results of geophysical logging acquired by our co-authors. Neutron and natural gamma log also are included.
-
- - p. 4, section 2.2., line 3: “mud” = “clay”? Please modify here if you agree, and elsewhere in the paper (same page line 6 for instance, Fig. 10).
- Reply: We would like to use mud. Many papers on the geology of Jeju Island use mud more than clay so we don’t confusion for readers.
-
- - p. 4, section 2.2., line 3: “bio-clastic sediments”. OK? Please indicate these lower and upper limits on Fig. 2. Correspondence is not very clear. Again, harmonize between text and fig 2 (and others if necessary): for instance, clinker vs scoria. Moreover, Fig. 2 should enable to provide info about (i) lithology and (ii) permeability (high/low for instance), for instance by drawing 2 logs for each obs. well. Moreover, small thickness lithologies cannot be identified. Revise legend (with colors?). It would enable to better understand what is meant by “upper aquifer” and “lower aquifer” p. 8.
- Reply: According to your comments. We explained the “bio-clastic shells”. We drew the boundary between lower and upper limits and revised Fig. 2 including the legend.
-
- - p. 4, section 2.2., lines 5 & 6-7 (also in section 4.1.): I would not speak about “groundwater conduits” and “interrupt GW flow” but respectively as “aquifers” and “aquicludes/aquitards” or “low permeability layers”. Otherwise, define what is a “conduit”.
- Reply: We agree with your comments. Accordingly, we have modified references and removed “groundwater conduits”. Times were synchronized and related local time. It is precise.
-
- p. 4, section 3.1.: N = 2. Please indicate then the considered time span. I feel the average is not the same for all groundwater level probes (Divers and multidepth probes). Moreover, I fear an error, the filtering is much more than 5 data (fig. 3).
- Reply: We performed from 2 to 10. N = 2 showed the most respond of earthquake and successfully removed the tendency of the tides.
-
- p. 4, section 3.2., line 2: what is the “hydraulic diffusion coefficient” (T/S?)? A table with all parameters used in the paper, and their units should be provided.
- Reply: We provide those information on Table 3.
-
- p. 4, equ. 2: there is a blanc within “Si n”.
- Reply: We revised the spacing words.
-
- p. 4, section 3.2.: delay time: you may explain that there might be an ambiguity if it exceeds the wavelength. Right?
- Reply: The equation is used in many papers and I think there is no problem.
-
- p. 6, section 4.1., lines 5-6: you may cite the order of magnitude of the amplitude: about 50 cm at SS1, a few cm at SS3. Right?
- Reply: We provide those information on Table 2.
-
- p. 6, section 4.1. (and others): use SI units (MKS): Transmissivity in m2/s.
- Reply: The range of hydraulic parameter units (transmissivity and specific capacity etc.) on Jeju Island was too large. Previous studies on Jeju Island also used m2/day.
-
- p. 6, section 4.1., second paragraph, lines 7-9: it is not clear how these results are reported in Table 3. It seems they are not.
- Reply: The equation is used in many papers and I think there is no problem.
-
- p. 7, section 4.1., first paragraph, first lines: I would rather intervert: The GW level changes are related to T, which is fixed, and not the opposite. Right? Same for lines 4 & 5; it suggests that the permeability is changing (linearly increasing).
- Reply: In the previous study, the changes in permeability due to earthquakes were discussed. Elkhoury et al. (2006) reported that an earthquake could affect the hydrological system, and the water level was changed due to the occurrence of earthquakes, related to aquifer permeability or transmissivity. Furthermore, an earthquake can change aquifer permeability (Brodsky et al., 2003; Manga and Wang, 2007; Wang et al., 2009). Several authors suggested that seismic waves may enhance rock permeability by removing precipitates and colloidal particles from clogged fractures, which in turn may lead to redistribution of pore pressure and changes of groundwater level in areas near a local pressure source (Matsumoto et al., 2003; Brodsky et al., 2003; Wang and Chia, 2008).
-
- p. 8, Fig. 5: would it be possible to add a scale for tides?
- Reply: We agree with your comments. We added a scale for tides.
-
- p. 8, line before the last one: flows vertically. Upwards or downwards?
- Reply: We agree with your comments. we modified the sentence.
-
- p. 10, line 2. Delete blank after EC.
- Reply: We agree with your comments. Accordingly, we revised the spacing words.
-
- Fig. 10: there is a need of a legend for the colors.
- Reply: We agree with your comments. Accordingly, we have modified Fig. 11(before modified Fig. 10).
-
- Lachassagne et. Al., 2011 and Petitta, et. Al., 2018.
- Reply: We agree with your comments. Accordingly, we have modified and added sentences with reference to the recommended paper.
Author Response File: 
Author Response.doc
Reviewer 2 Report
Dear Colleagues,
Nice paper, only some minor errors in text you should correct.
Best regards!
Comments for author File: 
Comments.pdf
Author Response
Response Letter
Date: March 06, 2019
To: Bojana Mijanovic
From: Soo-Hyoung Lee, [email protected]
Manuscript ID: water-451632
Title of the manuscript: Response Analysis of Multi-Layered volcanic aquifers in Jeju Island to the M 9.0 Tohoku-Oki Earthquake
Dear Bojana Mijanovic and Reviewer’s:
We are very pleased to submit the manuscript entitled ‘Response analysis of multi-layered volcaic aquifers in Jeju Island to the M 9.0 Tohoku-Oki Earthquake’ in Water. We fully reflected the advice of the Reviewer’s. Also, we received one more proceeding from MDPI English editing. The contents of the manuscript were revised, and the figures were revised and newly added. I state that the manuscript is original work. All the authors agree with the contents.
Enclosed are: the manuscript, 5 tables, and 11 figures.
(modified: 1 table, 3 figures / newly added: 1 figure)
The revised parts of the manuscript were indicated in blue color. Below, we stated our replies to the reviewer’s comments.
Review 1:
Dear Colleagues,
Nice paper, only some minor errors in text you should correct.
Best regards!
Reply: Thank you very much. We agree with your comments. Accordingly, manuscript is revised in order to reflect the reviewer’s comments.
Review 2:
I think that this paper is worth to be published but only after a major revision as either the presentation of the results, or the interpretations, or both must be improved. Then, the quality of the paper must particularly be strengthened as regards:
1. Better physically explaining and decomposing the various observed processes:
- wave transmission from the earthquake to the aquifer(observation wells). The fact that this is kind of process that is really observed must also be a bit more discussed to convince the reader; better explain and justify the physical processes that explain piezometric changes, and their relative amplitudes from one piezometer to the other;
Reply: We agree with your comments. We tried to make a better interpretation of this paper. The complemented paragraph was added to introduction. “Generally, when the seismic waves pass, the changes of pore pressure cause flow into and out of the well from aquifer by dynamic stress (seismic wave). The oscillatory changes in groundwater level occur when the aquifer has high enough transmissivity, permeability, etc.” Also, we mentioned results of the geophysical well loggings on result.
“Using a geophysical well logging system (2000 m length winch and Micro loggerⅡ produced by Robertson Geologging Co., United Kingdom), Natural gamma, neutron, vertical flowmeter, EC, and temperature logs were carried out at the speed of 3 m/min with a measuring interval of 1 cm. Fig. 5 is the results of those geophysical loggings in SS1 well before the M 9.0 Tohoku-Oki Earthquake [52]. The basalt formation until 135 m showed continuously both high and low porosity because the outside part of the basalt was cooled rapidly and the inside part of the basalt was cooled slowly. The neutron log showed those properties. The intervals with very high porosity between basalts are sedimentary formation. The formation below 135 m consists of the tuff with very high porosity relatively in SS1 well. Based on the natural gamma log, the basalt formation showed changeable values according to the components and the sedimentary environment when magma erupted. The tuff formation below 135 m showed high values of the natural gamma and the U formation below the tuff formation showed the highest values of the natural gamma. Based on the temperature logs, The temperature decreased from up to down until 60 m and the temperature below 60 m increased gradually as the geothermal gradient. Based on the EC logs, the EC increased dramatically at around 60 m caused by the effects of seawater intrusion until 80 m.”
2. Better interpreting the temperature and EC log presented at Fig. 2. Interpreting T and EC logs in unpumped wells is not straightforward as it must take into account possible vertical flow in the well that depend on the hydraulic head in each permeable level crosscut by the well. Logs can also be influenced by previous pumpings performed in the well. Then, the interpretation proposed in section 4.2. is not detailed enough to be convincing.
Reply: According to your comments, we revised section 2.2 and 4.2. Originally, we mentioned temperature and EC logs of SS-1, SS-2, and SS-3 on section 4.2. We moved contents of T and EC logs to section 2.2. for explaining Fig. 2. Also, we added results of well loggings (natural gamma, neutron, 1-D flowmeter, EC, Temperature log) acquired in SS-1 on section 4.2. for readers. Unfortunately, we could not acquire temperature and EC logs during the pumping test and we could not consider effects of the tide when performing geophysical loggings. But we made efforts to give a lot of information which we have about the borehole (SS1) to readers.
3. better interpreting and describing the changes observed after the earthquake.
Reply: Fig. 8 shows the changes of EC with data fore and after earthquake.
4. Then, to my opinion, Figs. 10 a and b must be revised.
Reply: According to your comments, we modified that the Fig. 11(before modified Fig. 10) a and b were revised.
5. Minor remarks
- a detail for next submission
- P.1, introduction, 1, line 4: earthquakes not only provoke compression or expansion of aquifers; they may also provoke changes of the hydrodynamic parameters, notable permeability. Overall, the recent paper from Petitta et al. may also be cited.
- Reply: We agree with your comments. Accordingly, we have modified and added a sentence.
- P.2, introduction, line 6: “in” is missing before “coastal”
- Reply: We agree with your comments. We corrected the word.
-
- P.2, introduction, line 8: “complex structure and hydro…”
- Reply: We agree with your comments. Accordingly, we revised the sentence.
-
- P.2, table 1: it would be nice to also have a column with piezometric level in masl. And to explain that DTW and piezo are mean values. Well radius: indeicate if drilling radius or tube radius
- Reply: We agree with your comments. Accordingly, we revised the table 1.
-
- p. 2, section 2.1., line 7, cite Fig 2 for location of probes.
- Reply: Fig. 2 is large-scale information of SS1-SS3. We have table 4 and Fig. 8 to give information of multi-depth probes in SS1 to readers.
-
- p. 2, section 2.1., line 11 and following, cite Fig 2, indicate exact location of Divers, as well as on figure 2. Indicate also the part of the well that is screened. Homogeneize text with figure: “transition zone” vs “mixing zone”. It would be nice to complete this section and fig 2 with a table summarizing all metrological parameters: location, type, measurement interval, etc..
- Reply: We agree with your comments. We indicated depth of screen on table 1. Two words are not different.
-
- - p. 3, section 2.2., line 1: “from bottom to top”.
- Reply: We agree with your comments. We added the expression.
-
- - p. 3, section 2.2., lines 4, 5: please rewrite it is not clear: from pumping tests, from time series, specific capacity = Q/s? Diffusivity = T/S
- . Reply: We agree with your comments. We modified the sentences and referred to previous study.
-
- - p. 3, section 2.2., line 7: indicate also which lithological facies are of low permeability.
- Reply: We agree with your comments. Accordingly, we mentioned low-permeability layers (U-formation and the Seogwipo formation).
-
- - p. 3, section 2.2., line 9: “permissive” = “permeability”? You mean due to weathering? Please precise.
- Reply: We agree with your comments. “permeability” is correct. We revised that word.
-
- - p. 4, section 2.2., line 1: really neutron log, not gamma ray? Please check.
- Reply: In section 4.2, we added contents about results of geophysical logging acquired by our co-authors. Neutron and natural gamma log also are included.
-
- - p. 4, section 2.2., line 3: “mud” = “clay”? Please modify here if you agree, and elsewhere in the paper (same page line 6 for instance, Fig. 10).
- Reply: We would like to use mud. Many papers on the geology of Jeju Island use mud more than clay so we don’t confusion for readers.
-
- - p. 4, section 2.2., line 3: “bio-clastic sediments”. OK? Please indicate these lower and upper limits on Fig. 2. Correspondence is not very clear. Again, harmonize between text and fig 2 (and others if necessary): for instance, clinker vs scoria. Moreover, Fig. 2 should enable to provide info about (i) lithology and (ii) permeability (high/low for instance), for instance by drawing 2 logs for each obs. well. Moreover, small thickness lithologies cannot be identified. Revise legend (with colors?). It would enable to better understand what is meant by “upper aquifer” and “lower aquifer” p. 8.
- Reply: According to your comments. We explained the “bio-clastic shells”. We drew the boundary between lower and upper limits and revised Fig. 2 including the legend.
-
- - p. 4, section 2.2., lines 5 & 6-7 (also in section 4.1.): I would not speak about “groundwater conduits” and “interrupt GW flow” but respectively as “aquifers” and “aquicludes/aquitards” or “low permeability layers”. Otherwise, define what is a “conduit”.
- Reply: We agree with your comments. Accordingly, we have modified references and removed “groundwater conduits”. Times were synchronized and related local time. It is precise.
-
- p. 4, section 3.1.: N = 2. Please indicate then the considered time span. I feel the average is not the same for all groundwater level probes (Divers and multidepth probes). Moreover, I fear an error, the filtering is much more than 5 data (fig. 3).
- Reply: We performed from 2 to 10. N = 2 showed the most respond of earthquake and successfully removed the tendency of the tides.
-
- p. 4, section 3.2., line 2: what is the “hydraulic diffusion coefficient” (T/S?)? A table with all parameters used in the paper, and their units should be provided.
- Reply: We provide those information on Table 3.
-
- p. 4, equ. 2: there is a blanc within “Si n”.
- Reply: We revised the spacing words.
-
- p. 4, section 3.2.: delay time: you may explain that there might be an ambiguity if it exceeds the wavelength. Right?
- Reply: The equation is used in many papers and I think there is no problem.
-
- p. 6, section 4.1., lines 5-6: you may cite the order of magnitude of the amplitude: about 50 cm at SS1, a few cm at SS3. Right?
- Reply: We provide those information on Table 2.
-
- p. 6, section 4.1. (and others): use SI units (MKS): Transmissivity in m2/s.
- Reply: The range of hydraulic parameter units (transmissivity and specific capacity etc.) on Jeju Island was too large. Previous studies on Jeju Island also used m2/day.
-
- p. 6, section 4.1., second paragraph, lines 7-9: it is not clear how these results are reported in Table 3. It seems they are not.
- Reply: The equation is used in many papers and I think there is no problem.
-
- p. 7, section 4.1., first paragraph, first lines: I would rather intervert: The GW level changes are related to T, which is fixed, and not the opposite. Right? Same for lines 4 & 5; it suggests that the permeability is changing (linearly increasing).
- Reply: In the previous study, the changes in permeability due to earthquakes were discussed. Elkhoury et al. (2006) reported that an earthquake could affect the hydrological system, and the water level was changed due to the occurrence of earthquakes, related to aquifer permeability or transmissivity. Furthermore, an earthquake can change aquifer permeability (Brodsky et al., 2003; Manga and Wang, 2007; Wang et al., 2009). Several authors suggested that seismic waves may enhance rock permeability by removing precipitates and colloidal particles from clogged fractures, which in turn may lead to redistribution of pore pressure and changes of groundwater level in areas near a local pressure source (Matsumoto et al., 2003; Brodsky et al., 2003; Wang and Chia, 2008).
-
- p. 8, Fig. 5: would it be possible to add a scale for tides?
- Reply: We agree with your comments. We added a scale for tides.
-
- p. 8, line before the last one: flows vertically. Upwards or downwards?
- Reply: We agree with your comments. we modified the sentence.
-
- p. 10, line 2. Delete blank after EC.
- Reply: We agree with your comments. Accordingly, we revised the spacing words.
-
- Fig. 10: there is a need of a legend for the colors.
- Reply: We agree with your comments. Accordingly, we have modified Fig. 11(before modified Fig. 10).
-
- Lachassagne et. Al., 2011 and Petitta, et. Al., 2018.
- Reply: We agree with your comments. Accordingly, we have modified and added sentences with reference to the recommended paper.
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
This review deals with the fist revision of this paper (second review).
A detail: I recommended to the authors to number the lines of their manuscript. It wasn’t done. It would have helped for this revision also.
Most of the proposals I made during the first review were taken into account.
However, I have still some concerns. The most important deals with the results themselves and the method to obtain them, and is developed below. The second issue deals with the presentation of these results that must be detailed enough to enable the reader understand how the interpretation was performed.
To summarize:
1. The authors must better interpret the data set, by coupling the EC well logs and the EC changes monitored at various depths by the probes (a same parameter measured differently).
2. Then they will be able to explain how water moves in the well due to tide, vertical water flow in the well, if any, etc.
3. Then, they will be able to understand what happens outside the well, in the aquifer
4. And finally compare the situation before and after the earthquake to conclude.
Some comments are still details and just follow.
1. As regards new sections added to the paper or important revisions:
- section 4.2.: it is nice to have introduced this paragraph as well as the new Figure 5.
-> as regard the form, I would suggest using the present rather than the preterit, to replace “those” (2 occurrences) by “these”, and “changeable” by “various”. The legend of fig5 is missing, as well as the significance of the crosses and arrows in the right column
-> as regards the content:
(i) I challenge the fact that all the alternation of high and low porosity in the basalt formation results from alternation of basalt and sediments. Do you have evidences from cuttings or cores that all these alternations are related to sediments? Figure 2 suggests that only 8 layers are related to sediments. I think that the others are related to scoria levels that may materialize thin lava layers. Clarifying this is important as scoria layers may be aquifers whereas massive basalt in between may not be aquifer
(ii) the temperature and EC logs of Figure 5 seems different from those of fig. 2. This is not an issue, but should be discussed and should help understanding what happen in this well.
Some details:
- as you kept “mud” instead of “clay”. Explain at the first occurrence that throughout the paper you mean “clay” when you write “mud”. It would enable international readers to understand
- Fig 2 is not revised enough (see my comments on the first manuscript). One must be able to identify all layers of the logs, even the thinnest ones
As regards may main comment:
1. I attached a figure with also manuscript comments on it
2. I explain what I understood from this data set
1. I put the main data from the paper on the attached figure. You will see that there are a few geological inconsistencies between Fig 2 and 11a (and also with Fig 5: gamma, CPS, LPU), but it doesn’t matter so much. However, it would be much clearer for the reader to have a unique and clear lithological log. And better, if possible and if it his known, which layers are pervious, and which are impervious (see below).
2. Then I wanted to understand from the geology and the EC and T° logs which layers are aquifer and which layers are impervious in this well. This is not clear for me before figure 11, and I think that this should be explained in the paper as soon as section 2.2.. In fact, as far I understand, the scope of the paper is to describe changes due to the earthquake and not the hydrogeology of the well
2a. It is not evident from the geological logs to distinguish aquifers and aquitards. From them, I would suspect a multilayer aquifer, but this is not consistent with Fig 11a (aquifer 1 and Aquifer 2). Can you describe much more in details the aquifers? I would suspect, from my experience:
i. Aquifers = scoria levels at the top and bottom of each lava flow. Is it what we observe for instance between about 75 and 105 m bgs?
ii. Aquifers = cooling fractures in the hearth of the lava flows. Is it what you mean by fracture zone on fig 11a?
iii. Aquitard = “mud”. Paleosoils, weathered layers
iv. Aquitard = silt and sand?
v. Medium K = sands ? or rather impervious?
vi. Aquitard = hyaloclastite
However, I insist, my experience may not be accurate in Jeju.
2b. In the text, you cite flowmeter measurements (section 4.2). Any data to be presented? It would be of huge interest if accuracy is OK
2c. The 2 EC logs have similarities, and also differences (Fig 2 and 5)
i. Water level (about -27 m) to -60 m: similar for both logs with about 1000 μS/cm and steady
ii. At about -60 m: sharp increase 1000 to 3000 (F2) or 10000 (F5)
iii. Then continuation of increase up to about 30000 at -70 (F2) or -75 (F5)
iv. Then, rather steady for F5 (30 to 50.000) but down back to about 18000 for F2 at a depth of 105 – 110 m
Depending on what we suspect from the permeability of rocks and/or the vertical flows in the well, if any, the interpretations may be very different:
- If for instance we have a continuous aquifer from at least piezo level to below -60, then the EC increase can really be the transition zone
- If for instance we have discrete aquifer (aquifer 1) only around 60, and no aquifer above, then the water is stagnant in the well between 60 and piezo level
- If for instance we have discrete aquifer (aquifer 1) around 60, and an aquifer above (let’s call it aquifer 0) with higher hydraulic head within aquifer 1 (as arrows from Fig 5 suggest), then the water is flowing upwards in the well and the salinity of water in aquifer 1 is less than 1000. Then flowmeter data are very important to interpret or also flowmeter and/or EC logs during pumping if such test was performed
- If the flow is downwards below 60 m, then it means that this aquifer is about 30000 μS/cm
- Then we can continue the interpretation downwards, step by step, but all data must be used to build a strong conceptual model of the well
2d. Temperature logs have also similarities and differences:
i. Decrease between 0 and 60 to about 16°C on both curves that might be due last summer
influence (if water is stagnant) or cool water upflow (but difficult to explain)
ii. Then increase from 16 to 18°C on both curves but with a more regular shape on F5 than on F2, with a “strong” increase on F2 between about 65 and 75 m, and an anomaly at about 110
From my experience, it is very difficult to interpret EC and T° curves if the well was not “steady” since a long time. It may keep in memory what happened previously such as pumping, moving a pump inside, etc.. This might also explain some of these anomalies and differences between the 2 curves. Do you have other logs? Did you keep a memory of what was done in the well before each log? Again, if you have logs performed during pumping, it would be much more straightforward to interpret.
3. You understand that depending on the EC vertical distribution in the well, the location of the EC probes, and the movements of water in the well (notably due to tides), the EC probes will record very various signal. Then Fig 6:
a. S1 is in the low salinity area and the EC changes are only due to the up down movement of water in the well. High EC at high tide and lower EC at low tide as EC seems to slightly increase downwards
b. S2 is at the 60 m anomaly and, the EC front is moving up and down in front of it (fresh-salty, fresh
salty, etc. 1000 - 30000). It means that the EC front is more looking like fig 2 than F5 (smoother front)
c. S3 is below the 60 m front in an area where EC decreases from about 10.000 μS/cm in about 2 m. It means that the EC log is not flat in that area or that F3 is very near the curve change observed in F2
d. S4 is not near a EC front, vertical EC only changes about 30 μS/cm / 2 m (daily tides changes)
It is then possible to reconstruct the EC gradient near each probe. But again, the variations observed at the probes depend on the EC log in the well, that may have been influenced by the history of the well. It is then very important to compare probes EC variations with recent well logs or to take into account what happened since the previous log.
4. Fig 8:
a. S1: no change before and after quake – it would suggest that the water is stagnant in S1 (above 60)
b. S2 no change; maybe a slight increase. The water column in the well moved a little bit upwards, which may be consistent with temperature increase if S2 is below the surface T° influence
c. S3: the water column in the well seems to have moved a little bit downwards. If the gradient is about 10000 μS/cm by 2m (Fig 6), then as we shifted from 33-44000 (before) to 25-35000 (after) then the shift is about 2 m downwards (Temperature doesn’t changed so much but decreased a little bit -> consistent)
d. S4: again an area with a small EC gradient as we don’t see much tide related EC variations. But EC increased from 22 to 30000 after the quake (and Fig9: T° decreased).
Based on EC & T° log from F2 (and F8) it means that the water column moved downwards in the well, but not much if the EC gradient is high
5. By confronting these interpretations with location of potential aquifers (§ 2 above) one may try to explain what happened during the quake in the well, and maybe outside the well in the aquifers
Comments for author File: Comments.pdf
Author Response
Response Letter
Date: March 06, 2019
To: Bojana Mijanovic
From: Soo-Hyoung Lee, [email protected]
Manuscript ID: water-451632
Title of the manuscript: Response Analysis of Multi-Layered volcanic aquifers in Jeju Island to the M 9.0 Tohoku-Oki Earthquake
Dear Bojana Mijanovic and Reviewer’s:
We are very pleased to submit the manuscript entitled ‘Response analysis of multi-layered volcaic aquifers in Jeju Island to the M 9.0 Tohoku-Oki Earthquake’ in Water. We fully reflected the advice of the Reviewer’s. Also, we received one more proceeding from MDPI English editing. The contents of the manuscript were revised, and the figures were revised and newly added. I state that the manuscript is original work. All the authors agree with the contents.
Enclosed are: the manuscript, 5 tables, and 12 figures.
(Modified: 3 figures / newly added: 1 figure)
The revised parts of the manuscript were indicated in red color (first review: blue color). Below, we stated our replies to the reviewer’s comments.
Review:
This review deals with the fist revision of this paper (second review).
A detail: I recommended to the authors to number the lines of their manuscript. It wasn’t done. It would have helped for this revision also.
Most of the proposals I made during the first review were taken into account.
However, I have still some concerns. The most important deals with the results themselves and the method to obtain them, and is developed below. The second issue deals with the presentation of these results that must be detailed enough to enable the reader understand how the interpretation was performed.
1. As regards new sections added to the paper or important revisions:
section 4.2.: it is nice to have introduced this paragraph as well as the new Figure 5.
-> as regard the form, I would suggest using the present rather than the preterit, to replace “those” (2 occurrences) by “these”, and “changeable” by “various”. The legend of fig5 is missing, as well as the significance of the crosses and arrows in the right column
Reply: Thank you for your comments, we corrected words and changed the Fig. 6.
-> as regards the content:
(i) I challenge the fact that all the alternation of high and low porosity in the basalt formation results from alternation of basalt and sediments. Do you have evidences from cuttings or cores that all these alternations are related to sediments? Figure 2 suggests that only 8 layers are related to sediments. I think that the others are related to scoria levels that may materialize thin lava layers. Clarifying this is important as scoria layers may be aquifers whereas massive basalt in between may not be aquifer
Reply: We referred to the geological logs of JeJu Special Self-Governing Province, not directly observing cuttings and cores of the wells SS1, SS2, and SS3. However, we described hydrogeological patterns in more detail, based on the geological logs and newly added figure 2 for the supplementary exhibition of hydrogeology.
Lines 90-100: The bottom part of the SS-1, SS-2, and SS-3 wells in the study area consists of Seogwipo formation (SGF) and U-formation (UF) that gradually become thicker from the coast to the center of JeJu island (Fig. 2). On the SS-1 well, porous hyalocalstites layer overlies the SGF and porous pyroclastite, sand, and agglomerate layers intercalate between basalt layers. Low-permeable sediments like clay, silt, and silty sand as exist in the upper part of the basalt layers at the SS-1 well. On the SS-2 well, permeable pyroclastite exists in the upper part and cataclastic zone indicated by dotted rectangle is also considered as a permeable zone. Low-permeable clay and silt layers are located between the basalt layers. On the SS-3 well, permeable pyroclastite layer and low-permeable clay layer occur between the basalt layers with repetition. Scoria/coarse-fragments layer, dotted rectangle, that is located in upper part of the SS3 well, also acts a permeable zone.
(ii) the temperature and EC logs of Figure 5 seems different from those of fig. 2. This is not an issue, but should be discussed and should help understanding what happen in this well.
Reply: On Fig. 6 (previous Fig. 5), the geophysical well logs of the well SS-1 were performed in open hole just after the well was drilled in 2002. By contrast, the temperature and EC logs (Figs. 3 and 9) were performed in the state of screened hole in 2004 so that there exists some difference between the two sets of log data.
Some details:
- as you kept “mud” instead of “clay”. Explain at the first occurrence that throughout the paper you mean “clay” when you write “mud”. It would enable international readers to understand
Reply: Thank you. Following your comments, we changed ‘mud’ to ‘clay’.
- Fig 2 is not revised enough (see my comments on the first manuscript). One must be able to identify all layers of the logs, even the thinnest ones
Reply: As you mentioned, we newly added figure 2 for explaining the geological log in more detail.
As regards may main comment:
I attached a figure with also manuscript comments on it. I explain what I understood from this data set.
Reply: Please see our response as below.
2. I put the main data from the paper on the attached figure. You will see that there are a few geological inconsistencies between Fig 2 and 11a (and also with Fig 5: gamma, CPS, LPU), but it doesn’t matter so much. However, it would be much clearer for the reader to have a unique and clear lithological log. And better, if possible and if it his known, which layers are pervious, and which are impervious (see below)
Reply: As you mentioned, we newly added figure 2 for explaining the geological log in more detail. Please also see the description of lines 90-100.
3. Then I wanted to understand from the geology and the EC and T° logs which layers are aquifer and which layers are impervious in this well. This is not clear for me before figure 11, and I think that this should be explained in the paper as soon as section 2.2. In fact, as far I understand, the scope of the paper is to describe changes due to the earthquake and not the hydrogeology of the well
Reply: According to your comments, we indicated permeable zones on the new figure 2.
2a. It is not evident from the geological logs to distinguish aquifers and aquitards. From them, I would suspect a multilayer aquifer, but this is not consistent with Fig 11a (aquifer 1 and Aquifer 2). Can you describe much more in details the aquifers? I would suspect, from my experience:
Reply: According to your comments, we indicated low permeable (clay, silt, SGF, and UF) and permeable (pyroclastite, hyaloclastite, sand, and agglomerate) on the new figure 2. Please also see the description of lines 90-100.
2b. In the text, you cite flowmeter measurements (section 4.2). Any data to be presented? It would be of huge interest if accuracy is OK.
Reply: The vertical flowmeter result is presented in figure 6. Please also see the lines 336-350:
The high permeability zones are also confirmed with the result of vertical flowmeter logging (Fig. 6). For instance, at SS-1 well, upward flow occurs at approximately 40 m depth of 1,000 μS/cm and then a weak flow takes place in the transition zone. The depth of 77 m in the zone of saltwater recorded downward flow and the zone below than 110 m showed a weak upward/downward flow. The result of the vertical flowmeter logging indicates that the groundwater from the aquifer at a depth of 40 m flows into the well and then mainly moves upward, flowing into to other aquifer. The saltwater flowing into at the 60-70 m zone produces pressure difference with fresh water flowing down from the upper part and then moves downward and finally flows out in the lower part of the well.
Accordingly, the vertical flowmeter logs showed a similar result with the EC log in the SS-1 well, helping to understand groundwater flow in the multi-layered aquifer by the influence of the earthquake.
2c. The two EC logs have similarities, and also differences (Fig 2 and 5)
Reply: On Fig. 6 (previous Fig. 5), the geophysical well logs of the well SS-1 were performed in open hole just after the well was drilled in 2002. By contrast, the temperature and EC logs (Figs. 3 and 9) were performed in the state of screened hole in 2004 so that there exists some difference between the two sets of log data. The overall pattern of the two logs is similar each other even if the logging time between two logs (Figs. 2 and 6) are different.
2d. Temperature logs have also similarities and differences:
Reply: On Fig. 6 (previous Fig. 5), the geophysical well logs of the well SS-1 were performed in open hole just after the well was drilled in 2002. By contrast, the temperature and EC logs (Figs. 3 and 9) were performed in the state of screened hole in 2004 so that there exists some difference between the two sets of log data. The overall pattern of the two logs is similar each other even if the logging time between two logs (Figs. 2 and 6) are different.
From my experience, it is very difficult to interpret EC and T° curves if the well was not “steady” since a long time. It may keep in memory what happened previously such as pumping, moving a pump inside, etc. This might also explain some of these anomalies and differences between the 2 curves. Do you have other logs? Did you keep a memory of what was done in the well before each log? Again, if you have logs performed during pumping, it would be much more straightforward to interpret.
Reply: We performed geological logging (Figure 6) not during pumping.
3. You understand that depending on the EC vertical distribution in the well, the location of the EC probes, and the movements of water in the well (notably due to tides), the EC probes will record very various signal.
Then Fig 6:
a. S1 is in the low salinity area and the EC changes are only due to the up down movement of water in the well. High EC at high tide and lower EC at low tide as EC seems to slightly increase downwards
b. S2 is at the 60 m anomaly and, the EC front is moving up and down in front of it (fresh-salty, fresh salty, etc. 1000 - 30000). It means that the EC front is more looking like fig 2 than F5 (smoother front)
c. S3 is below the 60 m front in an area where EC decreases from about 10.000 μS/cm in about 2 m. It means that the EC log is not flat in that area or that F3 is very near the curve change observed in F2
d. S4 is not near a EC front, vertical EC only changes about 30 μS/cm / 2 m (daily tides changes)
It is then possible to reconstruct the EC gradient near each probe. But again, the variations observed at the probes depend on the EC log in the well, that may have been influenced by the history of the well. It is then very important to compare probes EC variations with recent well logs or to take into account what happened since the previous log.
Reply: Thank you for your comments. In relation to Fig. 7 (previous Fig. 6), we added your comments from the 248 to 255.
4. Fig 8:
a. S1: no change before and after quake – it would suggest that the water is stagnant in S1 (above 60)
b. S2 no change; maybe a slight increase. The water column in the well moved a little bit upwards, which may be consistent with temperature increase if S2 is below the surface T° influence
c. S3: the water column in the well seems to have moved a little bit downwards. If the gradient is about 10000 μS/cm by 2m (Fig 6), then as we shifted from 33-44000 (before) to 25-35000 (after) then the shift is about 2 m downwards (Temperature doesn’t changed so much but decreased a little bit -> consistent
d. S4: again an area with a small EC gradient as we don’t see much tide related EC variations. But EC increased from 22 to 30000 after the quake (and Fig9: T° decreased).
Reply: Thank you for your comments. In relation to Fig. 9 (previous Fig. 8), we added your comments from the 269 to 277.
Based on EC & T° log from F2 (and F8) it means that the water column moved downwards in the well, but not much if the EC gradient is high
Reply: Based on the flowmeter log, groundwater moves downwards which coincides with slight EC decrease vertically as shown in Fig. 9.
5. By confronting these interpretations with location of potential aquifers (§ 2 above) one may try to explain what happened during the quake in the well, and maybe outside the well in the aquifers
Reply: Please see the lines 343 to 355:
In the study area, the aquifers at the SS1 well site consist of the upper and lower aquifers based on geophysical well loggings and seismic waves destroyed the equilibrium between fresh water and saltwater in the SS1 well (Fig. 12(a)). EC values at the S1 and S2 depths increased due to upward groundwater movement and the turbulence in the aquifer 1 during seismic wave passing. The decrease of EC values at the S3 depth resulted from fresh water inflow from the aquifer existing between the S2 and S3 depths. The gradual increase of low EC values near the S4 depth reflects saltwater injection by the seismic waves from aquifer 2. Since fresh and saline water flowed into the SS1 well from the upper and low aquifers, the EC values of the S3 and S4 depths were maintained after the EC change (Fig. 12(b)). The groundwater changes in the SS1 well due to the Tohoku-Oki earthquake appear to have been accompanied by various unexplained mechanisms. Nonetheless, the multi-depth monitoring system characterized the multi-layer aquifers through which groundwater freely move caused by earthquakes and seismic waves, overcoming the limitation of ingle depth measurement.
Author Response File: Author Response.doc
Round 3
Reviewer 1 Report
The paper was really improved and can now be published.
I made a few additional proposals on the attached reviewed manuscript that may be taken into account into final version.
Author Response
We agree your comments (words)
Thank you for your academic advice and comments, we improved our manuscript.
