On the Possibility of Detecting Pore Pressure Changes in Marine Sediments Using Bottom Seismometer Data
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsTikhotskiy et al present a method to use bottom seismometer to detect overpressure in shallow unconsolidated seafloor sediments. Accompanied by well log data, the method can detect over pressurized zones, and could be used to monitor overpressure zones. The theory part is complex but well laid out. In general, the manuscript is well written and, after necessary modifications, suggested for publication.
Major issues:
- Ln. 175. The Gassmann equation (A5) used in this study works best for very low frequency (<100 Hz ) data. However, the frequency of boomer and spark sources is higher, and research even suggests using frequencies up to 1000 Hz. How will this affect the results? In many places, Gassmann was mistakenly typed as Gassman.
Another issue is that the Gassmann's equation does not address the possible presence of hydrocarbons in pores, such as methane hydrates in cemented sediments. It can include the contribution of hydrocarbons, but it requires methods other than seismometers, such as resistivity measurement.
- Ln. 265. The maximum pore pressure is limited to the total overburden. However, for hydrocarbon reservoirs, in the case of methane hydrate dissociation, the pore pressure can be much higher than that of the overlying layer. Discussion is needed.
- Ln. 439. Typical seismometers cannot cover such a wide frequency range. If there were no ideal seismometers, for example, if the high frequency is limited to 100 Hz, what would the result be?
Minor issues:
- Ln. 388. Here, should “Figs. 1, 2” be Figs. 6 , 7 ??
- Ln. 447. What are nonmeasurable parameters? Give a few examples.
- Data should be hosted on easily accessible public websites such as zenodo instead of mail.ru
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis text is well written and organized. The manuscript seems to be suitable for publication. This work corresponds to the content of the Journal of Marine Science and Engineering and can be published there after minor mentioned corrections.
1) How you define the “overpressure zone” in marine sediments? The problem is when the pore pressure is much higher than the geostatic (hydrostatic) pressure and here the difference is only a few bars.
2) Results in Figure 3 look very similar. Is the difference between models statically significant?
3) I do not understand the point to simulate seismic curves if not to compare them with real field data. It seems that Authors have the seismic profile of the well and here should be shown how it differ from synthetic curves. I do not support a situation where data is artificially divided to write several articles.
4) Why Authors recommend to use the frequency range as wide as 0.1-1000 Hz hence only very high and ultrahigh resolution seismic provides a good resolution?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors analyze the possibility to detect overpressure zones in marine sediments by using bottom seismometer data, and the physical bases are demonstrated by performing intensive calculation. The motivation is clear, and the calculation seems reasonable. Based on the results, suggestions are provided for the development of on-site testing and monitoring technologies. However, there are still some issues which needs further clarification, and my comments are as follows:
Equation 1: Dimensions are not consistent.
Line 167: Physical significances of the parameters e0 and Cc are clear, why should they be considered as fitting parameters? They can be determined by performing consolidation test on marine sediments.
Lines 181-190: Explanation of the N-dimensional mesh method is unclear.
Figure 2: There are obvious peaks representing overpressure zones in the consolidation-analysis cure. It is great. However, is there any survey data available to show the exact location of overpressure zones in nature? How to well demonstrate the reliability or validity of the pore pressure prediction? In addition, parameter values adopted for the calculation are not given.
Line 245: Why do the authors choose 37% as the critical porosity? On what basis? If the critical porosity has other values, will the results change? Why?
Line 261: It is better to always keep % following numbers (i.e., from 27% to 67%).
Line 267: What is the physical significance of factor A? How to choose the exact value between 0 and 1?
Line 286: If this assumption is not adopted, will the results change? Why? We should always make sure that the results are not assumption(s) and parameter value(s) dependent.
Line 302: What is the exact location indicating “the velocity drop may attain 26% …” in Figure 3?
Figures 3 and 4: Subfigures in Figure 3 are of very different axis arrangements from those in Figure 4. It is better in the same arrangement (e.g., to clockwise rotate all the subfigures in Figure 3 for 90 degrees). In addition, there is no shear velocity curves in Figure 3, and the symbol Vs in Figure 4 is better in orange color just like the color of the curves.
Lines 451-473: The description focusing on the importance and procedure of the study is not suitable here. Instead, only a brief summary focusing on what have been done is needed, and more efforts should be pay on the direct results supporting by theoretical, numerical, and/or experimental data. Thus, the conclusion needs a thorough revision.
Comments on the Quality of English LanguagePlease try to rewrite the long sentences into short ones.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsThanks a lot for the careful revision. Each three subfigures in Figures 3 and 4 are suggested to be put into one line just like the model in Figures 5 and 6. Beyond that, I have no further comments.
