Electrical Properties and Anisotropy of Schists and Fault Rocks from New Zealand’s Southern Alps under Confining Pressure
Round 1
Reviewer 1 Report
This is a very interesting study of a major structure for structural geology and geodynamics. My main concern is about the conclusion of the paper which I consider insufficiently demonstrated, and possibly arguable. The main result is that the mylonite resistivities wouldn't depend of porosity, which is not so clear (figure 7: the trend is 3 x less important thant for schist, which doesn't make it independent at all). This argument is so important to the paper that figures should cleraly illustrate the porosity/resistivity relationship. Such a plot is not presented and would be necessary.
l38: comma misplaced (before [14])
Figure1: I recommend to add the approximate position of samples on the figure.
Figure 2: Later in the paper, reference to the fabric of seral samples is given. I would recommend to add a photomicrograph fot the 8 samples in order to be able to compare the fabrics whichi are very important for the discussion of this study.
l134-140: especially l.137: The sentence doesn't seem grammatically correct. Cutting it in two sentences with small reformulation should solve the question.
l148: 'etch pit' doesn't seem very conventionnal. I suggest to bracket the term.
l. 150: remove comma after [52]
l.177-180: This sentence and Equation are not used in the paper. I recommand to remove it.
L. 201-202: "replicating the anisotropic behavior of the rocs under in-situ conditions ... by a power functions". The sentence isn't clear enough. Needs reformulation.
l. 211: "Samples were initially evacuated " : You mean the water was removed from the sample by this process. Precise that the procudre is adopted to dry the samples.
l. 212: first appearance of DI, develop the words full.
l. 214-216: Something wrong with md and ms: Needs verification (I suppose md is for dry. could be expressed clearly. Same for ms) Presently, the equation is wrong
l. 223: "to minimize the effects of fabric anisotropy": could add "on the resistivity"
l. 266 and Table 1: Inconsistency between text and Table 1 concerning 08B1 (measured in only one direction in the Table)
Table 1: Add a line with the measured porosity and a line with the distance to the fault of the sample .
l. 304: "resistivty"
l. 305 and figure 6: "different trends": Discussing trends for mylonites after figure 6 is not convincing because the scale doesn't permit to show the trend. Either make or add a different graph for shists and mylonites or remove sentence. I wonder if using a log scale on distance couldn't permit to show the two trends on the same graph. Could be tested.
"Schist porosity decreases logartihmically": Show a logarithmic fit curve directly on the figure
l. 307: "correspondinly" to be corrected (TBC)
Figure 6: Add a crossplot of porosity against Resistivity which would strongly support the commentaries and discussions
l.316: "OB1" to be checked
l. 333: this first sentence needs the crossplot porosity / resistivity (cf fig. 6)
l. 339: "closure of pores first during dislocation" : the sentence should be developed.
l: 339-340: A discussion of fabric evolution observed from photomicrograph would be useful here to ascertain the argument (cf commentaries to fig.2).
l. 341-343: Arguable, but the proposition made for fig. 6 (second plot with different scale to show clearly the evolution of mylonites would make it more clear).
l 402: "peff" correct to Peff.
l. 408: "Our observation that mylonites exhibit a porosity independent electrical response": The assertion is too strong compared to the data. Even Ultramylonite sample shows a decreasing trend with effective pressure. Sentence should be moderated.
l. 423: "our study also found that the low resistivities of mylonite are independent of porosity": same as above.
Paragraph Source of the Southern Alps Electrical Conductor (l419-427): the point here is to reject the idea that the SAEC would result of an interconnected saline fluid network. The argument depends of your assertion that "the mylonites resistivity are independent of porosity", which I am not convinced of from the data presented. Thus the lst sentence should be reformulated since the data are not decisive enough to reject the saline fluid hypothesis.
l. 431: "(Figure 4a)" to be corrected
l. 436: This conclusion is not clearly demonstrated, at least visually Needs the por/resistivity plot. After the given figures, "independent" seems to strong. Seems to be about 3 times less dependent than Schists.
l. 445: "transpot" to be corrected
Author Response
We hope that this revised manuscript is now suitable for publication in Geosciences.
Kind regards
Emma Kluge (on behalf of all co-authors).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript: geosciences-1454509 titled “Electrical properties and anisotropy of Alpine Fault rocks under confining pressure”, presents an interesting research study. The manuscript is well written, with Figures being correctly displayed and very informative. Results from the confining pressure experiments as well as the data from the anisotropy of resistivity provides the necessary support for the discussion section. Conclusions and Abstract are balanced, well written, and successfully display the major outlines of this paper. Therefore, I suggest that this paper should be published in its present form in the Journal of “geosciences”.
Author Response
Dear Reviewer,
Thank the reviewers for positive feedback on our manuscript.
Kind regards,
Emma Kluge (on behalf of all co-authors).
Reviewer 3 Report
It is interesting that authors explored the source of this anomaly by measuring the electrical properties of samples coHected from surface outcrops approaching the AFZ that have accommodated a range of systematic strain and deformation conditions. We investigated the effects of tectonite fabric, fluid saturated pore/fracture networks and surface conductivity on the buUc electrical response and the anisotropy of resistivity measured under increasing confining pressure.
Significance of content is high,and Scientific Soundness is good,I think it can be accepted in present form.
Author Response
Dear Reviewer,
Thank you for the positive feedback on our manuscript.
Kind regards,
Emma Kluge (on behalf of all co-authors).
Round 2
Reviewer 1 Report
Hello,
I suggest few modifications:
l.58 « structured »
l. 248 : The explanation remains confusing. It seems that you applied an hydrostatic weighting method. But I am not sure since your explanation doesn’t fit with the procedure.
In case of hydrostatic method, mS would be the mass of the saturated sample, not the mass of the sample when submerged in DI Water.
You should introduce mH which IS the mass of the sample when submerged in DI Water. Doing so allows to get the Volume of the sample V (mS-mH=rho_water x V due to Archimed force).
Then porosity =(mS-mD)/(mS-mH) (or (mS-mD)/(rho_water x V), but the previous formula is preferable).
If I mis-understood and you used a different method / procedure, then you need to clarify it.
By the way the formula (5) as stated in your draft doesn’t appear correct.
Table 1 : Too much dgits for porosity. Remove the last digit for each value.
l.352 : « schist resistivity increases » : add approaching the AFZ
l. 358 : dominated : TBD (tense)
l.459 : correct « dominants »
l. 559-562 ; « This supports … on mineral surfaces. »
I don ‘t agree with the begining of the sentence : « this supports ».
It would be seem more appropriate to say that the processes you are invoking would could explain what is observed on MT profile.
Author Response
Responses to Reviewer 1:
Hello,
I suggest few modifications:
l.58 « structured »
Was unable to find a “structure” or “structured” near line 58 that was used incorrectly. It may have already been corrected.
- 248 : The explanation remains confusing. It seems that you applied an hydrostatic weighting method. But I am not sure since your explanation doesn’t fit with the procedure.
In case of hydrostatic method, mS would be the mass of the saturated sample, not the mass of the sample when submerged in DI Water.
You should introduce mH which IS the mass of the sample when submerged in DI Water. Doing so allows to get the Volume of the sample V (mS-mH=rho_water x V due to Archimed force).
Then porosity =(mS-mD)/(mS-mH) (or (mS-mD)/(rho_water x V), but the previous formula is preferable).
If I mis-understood and you used a different method / procedure, then you need to clarify it.
By the way the formula (5) as stated in your draft doesn’t appear correct.
Table 1 : Too much digits for porosity. Remove the last digit for each value.
Porosity reduced to three significant figures.
l.352 : « schist resistivity increases » : add approaching the AFZ
Correction made.
- 358 : dominated : TBD (tense)
“Dominated” changed to “dominates”.
l.459 : correct « dominants »
Correction made.
- 559-562 ; « This supports … on mineral surfaces. »
I don ‘t agree with the beginning of the sentence : « this supports ».
It would be seem more appropriate to say that the processes you are invoking would could explain what is observed on MT profile.
“This supports our prior inference….” was changed to “This may coincide with our prior inference….”
Author Response File: Author Response.pdf
