Numerical and Probabilistic Study on the Optimal Region for Tsunami Detection Instrument Deployment in the Eastern Sea of Korea

Round 1

Reviewer 1 Report

Dear authors,

It has been a pleasure to read through your manuscript. The paper is well organised and results are clearly presented. I recommend that it can be accepted after some minor revisions.

**comments on optimal site selection: from scientific point of view without legal/political considerations, would an area between Yomato Rise and the west coast of Japan (Tohoku-Hokkaido), just west of the high seismicity belt where large earthquakes occurred in the past, be a better option? A site in this area would meet the criteria and it could provide a much earlier detection. Unlike earlier generation model, newer generation DART 4G sensors can be placed quite close to seismic sources.

**Comments on quality improvements:

• Figure 1 on page 7 should be Figure 5.
• Figures 3 & 7: need to improve the quality of these two figures, hard to read in their current forms. Font sizes are too small, resolution is also too low.
• For color scale ticks/labels in Figures 3, 6,, 7, 9, 10 and 11(b): since colour scale shows probability, it will be better to use percentages than decimals, e.g. change 0.1 to 10%.

Regards,

 

 

Author Response

Response to Reviewer 1 Comments

 

We thank Reviewer 1 for the considerate comments. We respect your point-by-point comments and revised the manuscript with highlighting using track changes function in Microsoft Word.

 

Point 1: From scientific point of view without legal/political considerations, would an area between Yomato Rise and the west coast of Japan (Tohoku-Hokkaido), just west of the high seismicity belt where large earthquakes occurred in the past, be a better option? A site in this area would meet the criteria and it could provide a much earlier detection. Unlike earlier generation model, newer generation DART 4G sensors can be placed quite close to seismic sources.

Response 1: Yes. in point of view without legal/political considerations, the location near the potential tsunami sources on the west coast of Japan is an optimal region for deploying tsunami observation instruments, like DART 4G sensors, in terms of tsunami early warning. We thank the comment in the scientific point of view.

 

Point 2: Figure 1 on page 7 should be Figure 5.

Response 2: We thank the reviewer for pointing out our mistake. We have changed “Figure 1” into “Figure 5” (Refer to Line 179).

 

Point 3: Figures 3 & 7: need to improve the quality of these two figures, hard to read in their current forms. Font sizes are too small, resolution is also too low.

Response 3: We have changed figure 3&7 which has larger font size and higher resolution than before figures (Refer to Line 119, 257).

 

Point 4: For color scale ticks/labels in Figures 3, 6,, 7, 9, 10 and 11(b): since colour scale shows probability, it will be better to use percentages than decimals, e.g. change 0.1 to 10%.

Response 4: We respect the reviewer’s comment. So we have changed color scale labels, which indicates probability from the decimals to the percentages in Figure 6, 9, and 10 (Refer to Line 214, 314, and 316). However, since the color scales of Figures 3 and 7 show initial sea-surface displacement and maximum tsunami wave height distribution, color scale labels were used as decimals in Figures 3 and 7.

Author Response File: Author Response.docx

Reviewer 2 Report

This study proposes the method for optimal area for offshore tsunami observation instrument installation under the limited condition that the tsunami source in out of the territorial sea by investigating areas with the highest tsunami detection probability along with maximization of evacuation time and bottom slope conditions.

Broad comments

1. The criteria for choosing the set of potential tsunami scenarios, which are used in computational experiments is not clear. The question that then arises is why there is so big difference between the initial water surface elevations in taken tsunami sources? (See parameter D in Table A1). In addition, the orientation (azimuth) of sources seems to be not realistic in some cases. For example, the inundation parts of sources near Akita coast are being seaward, and elevation parts – coastward. However according to the paper (Aida I. A source model of the tsunami accompanying the 1983 Nihonkai-Chubu earthquake. - Bull. Earthq. Res. Inst. Tokyo Univ. 59, 1984, 93-104, (in Japanese)) the elevation part of the initial water surface displacement at tsunami source in 1983 was turned seaward. Maybe the source orientation is not important for the far-field wave height distribution. But, this fact must be proven by computations.
2. The description of MLE method (lines 53-63) is not clear enough. I recommend authors to describe the procedure for obtaining the probability value in more detail (not in general case but for problem under consideration). The reference [26] where detail explanation of MLE can be found doesn’t work.
3. As I understood, the criterion for tsunami detection instruments deployment site is the highest probability of tsunami appearance there with limited height and the travel-time reserve. According to this, some water areas above the Yamato Rise is more preferable for deployment than area around Ulleung-do Island. Why this location is not regarded as suitable place for tsunami detection instruments deployment?

 

Specific comments

1. Lines 35 and 59. S-net is the subsystem of DONET. Every DONET station includes seismometer and tsunameter (ocean level meter). S-net is used for obtaining earthquake source parameters (not tsunami height). It is better to replace “S-net” by “DONET”.
2. Line 43. Among tsunami researches the tsunami of 1993 near Hokkaido is called “Okusiri tsunami of 1993”.
3. Line 108. Instead of “bottom geometry” is better to use “bottom topography”.
4. Line 124. Instead of “ocean bottom slope” is better to write “ocean bottom slope angle”.
5. Line 132. Tsunami energy is proportional to squared wave height.
6. Line 142. Maybe authors mean “underwater mountain ridge”.
7. Line 157. Instead of “equation” is better “expression” or “formula”.
8. Line 162. I recommend to eliminate the word “fault”.
9. Line 173. Change “lined” by “outlined”.
10. Line 213. “da delay” ???
11. Line 275. It seems to me that tsunami source parameters determination in the near-field case is much more differs from far-field cases.

 

 

Author Response

Response to Reviewer 2 Comments

 

We thank Reviewer 2 for the considerate comments. We respect your point-by-point comments and revised the manuscript with highlighting using track changes function in Microsoft Word.

 

Point 1: The criteria for choosing the set of potential tsunami scenarios, which are used in computational experiments is not clear. The question that then arises is why there is so big difference between the initial water surface elevations in taken tsunami sources? (See parameter D in Table A1). In addition, the orientation (azimuth) of sources seems to be not realistic in some cases. For example, the inundation parts of sources near Akita coast are being seaward, and elevation parts – coastward. However according to the paper (Aida I. A source model of the tsunami accompanying the 1983 Nihonkai-Chubu earthquake. - Bull. Earthq. Res. Inst. Tokyo Univ. 59, 1984, 93-104, (in Japanese)) the elevation part of the initial water surface displacement at tsunami source in 1983 was turned seaward. Maybe the source orientation is not important for the far-field wave height distribution. But, this fact must be proven by computations.

Response 1: We thank the Reviewer 2 pointing out the important thing. We realized the description of Table A1 was insufficient. So, we added a description for detailed information on potential tsunami scenarios we used (Table A1).

Line 69 - 81 in main text: To figure out the optimal region for tsunami observation instrumentation, this study only focused on the potential tsunami scenarios that can affect the east coast of Korea and used in previous studies. Cases 1-15 in Table A1 were selected and extended from potential tsunami scenarios suggested by the Disaster Control Research Center, Tohoku University, in 1995. Extended parameters in cases 1-15 from potential tsunami scenarios were calculated based on earthquake seismic gap, fault along the Okhotsk plate boundary located on the west coast of Japan. Case 17, 19, 23, and 26, respectively, are the Shakotan-oki earthquake (2 August 1940), Nigata earthquake (16 June 1964), Akita earthquake (26 May 1983), and Okusiri earthquake (12 July 1993) which are caused tsunamis and has different seismic moments. According to Choi and Hong (2001), cases 16 – 27 were calculated for the purpose of the numerical simulation of tsunami wave propagation to the Korean coast based on these historical earthquakes. Other cases consist of the magnitude eight potential tsunami scenarios suggested by the Korean Peninsula Energy Development Organization (KEDO) in 1999.

 

Point 2: The description of MLE method (lines 53-63) is not clear enough. I recommend authors to describe the procedure for obtaining the probability value in more detail (not in general case but for problem under consideration). The reference [26] where detail explanation of MLE can be found doesn’t work

Response 2: We agree with the reviewer comment that we did not fully explain the procedure for obtaining the probability value in more detail. So, we added and re-wrote the description in detail under consideration as following:

Line 194 - 199 in main text: as results of the numerical modeling. It was assumed that the occurrences of 39 tsunami scenarios were all independent. The probabilities of tsunami propagation above each standard wave heights in all grids of numerical modeling were calculated. And then, MLE results of each standard wave heights were obtained by the sum of the log probabilities. The location where has higher MLE matches the higher tsunami detection probability area because tsunamis propagate with different parameters more frequently in this region.

 

And we have changed the reference [26] into a refereed journal instead of website information based on the reviewer's comment.

 

Point 3: As I understood, the criterion for tsunami detection instruments deployment site is the highest probability of tsunami appearance there with limited height and the travel-time reserve. According to this, some water areas above the Yamato Rise is more preferable for deployment than area around Ulleung-do Island. Why this location is not regarded as suitable place for tsunami detection instruments deployment?

Response 3: We agree with the reviewer’s comment. However, it is very difficult to deploy Korea’s tsunami observation instruments near the Yamato Rise because of legal/political considerations. Yamato Rise is far away from the territorial sea of Korea so that the Korea government cannot deploy their own instruments near the Yamato Rise. That’s why we suggested northeast of Ulleung-do as the optimal region for tsunami instrumentation.

 

Point 4: Lines 35 and 59. S-net is the subsystem of DONET. Every DONET station includes seismometer and tsunameter (ocean level meter). S-net is used for obtaining earthquake source parameters (not tsunami height). It is better to replace “S-net” by “DONET”.

Response 4: We thank the reviewer for pointing out our mistake. We have changed “S-net” to “DONET” (Refer to Line 35, 62).

 

Point 5: Line 43. Among tsunami researches the tsunami of 1993 near Hokkaido is called “Okusiri tsunami of 1993”.

Response 5: We changed the word by following the reviewer’s comment (Refer to Line 41-42).

 

Point 6: Line 108. Instead of “bottom geometry” is better to use “bottom topography”.

Response 6: We agree with the reviewer’s comment so we used “bottom topography” instead of “bottom geometry” (Refer to Line 129).

 

Point 7: Line 124. Instead of “ocean bottom slope” is better to write “ocean bottom slope angle”.

Response 7: We thank Reviewer 2 for the considerate comments and added “angle” (Refer to Line 145).

 

Point 8: Line 132. Tsunami energy is proportional to squared wave height.

Response 8: We made a mistake. So we added “squared” (Refer to Line 158).

 

Point 9: Line 142. Maybe authors mean “underwater mountain ridge”.

Response 9: We changed the word by following the reviewer’s considerate comments (Refer to Line 169).

 

Point 10: Line 157. Instead of “equation” is better “expression” or “formula”.

Response 10: We changed the word by following the reviewer’s considerate comments (Refer to Line 185).

 

Point 11: Line 162. I recommend to eliminate the word “fault”.

Response 11: We agree with the reviewer’s comment so we eliminated the word “fault” (Refer to Line 198).

 

Point 12: Line 173. Change “lined” by “outlined”.

Response 12: We made a mistake. So we changed from “lined” to “outlined” (Refer to Line 212).

 

Point 13: Line 213. “da delay” ???

Response 13: We thank the reviewer for pointing out our mistake. We eliminated “da” (Refer to Line 288).

 

Point 14: Line 275. It seems to me that tsunami source parameters determination in the near-field case is much more differs from far-field cases.

Response 14: We thank the reviewer for pointing out the important comment. We agree with the reviewers’ comment. We meant that, since we should consider far-field tsunami cases due to limitations, such as the territorial sea of Korea, we applied the method for optimal instrumentation of near-field tsunami cases to far-field tsunami cases. We did not determine tsunami source parameters but used them as an input of COMCOT to simulate tsunami propagation from the source to determine the optimal location for tsunami detection in the Korean territorial sea (Refer to Line 355).

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Reviewer remarks 2

The authors did a great work to sugest all my remarks.

Only two minor corrections:

Line 74 (in PDF file) Use “Okushiri” instead of “Okusiri” (This was my fault in review 1).

Line 121 Write “topography” instead “topohraphy”.

Author Response

We thank Reviewer 2 for the considerate comments. We respect your point-by-point comments and revised the manuscript with highlighting in gray color.

 

Point 1: Line 74 (in PDF file) Use “Okushiri” instead of “Okusiri” (This was my fault in review 1).

Response 1: We changed the word by following the reviewer’s comment (Refer to Line 41).

 

Point 2: Line 121 Write “topography” instead “topohraphy”.

Response 2: We thank the reviewer for pointing out our mistake. We have changed “topohraphy” to “topography” (Refer to Line 129).

Author Response File: Author Response.docx