Imaging of the Upper Mantle Beneath Southeast Asia: Constrained by Teleseismic P-Wave Tomography

Round 1

Reviewer 1 Report

Review for Shi et al. “Imaging of the crust and upper mantle beneath the Southeast Asia: Constrained by teleseismic P wave tomography”.

This is an interesting manuscript on the visualization of the lithosphere structure and location of paleo subduction slabs in southeast Asia. The manuscript is suitable for a wide audience and should be published after a moderate revision. I have a few issues that should be fixed prior to publication.

1. I wonder why this manuscript was sent to “remote sensing”. In this journal I expect topics that deal with datasets derived from airborne or spaceborne instruments.

2. Please set a space between the number and the SI unit (e.g., line 114, 122, 233, 256, 257, 261, 262, 263, 290, 295, 303, 306, 364, 367, 373, 388, 389).

3. The method section is rather long. Is it necessary to present all the formulas for the inversion? If so, what is the difference to other studies that use P wave tomography? Did you develop a new approach? This part of the manuscript (lines 142 – 286) is more a kind of review paper, not a research article.

4. The discussion is not really a discussion. It starts quite well with the reflection of previous research (lines 344 – 360). However, the rest of the discussion is more a description of results.

Author Response

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Reviewer 2 Report

The text should undergo detailed proofreading (some sentences should be reformulated, some statements should be more clearly expressed, a large amount of grammatical errors should be corrected). Descriptions of methods and some figures should be more detailed. All parts concerning the interpretation of the results in the first 90 km depth (due to the vertical resolution of the model) should be eliminated. The interpretation of the deeper structure (below 200 km) seems reasonable and convincing.

Other comments are inserted in the attached pdf document.

Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

Review “ Imaging of the crust and upper mantle beneath the Southeast Asia: Constrained by teleseismic P wave tomography”

This is a generally very nice paper, but I have some major comments that need to be addressed and reviewed before I would consider this study for publication.

General comments:

• You mention the crust in your title, but no mention once in the main text. The crust is important (see comments below) and needs to be considered.
• This journal seems a little out of context for seismic tomography (which is not really a remote sensing technique, from my point of view).
• I did some more detailed language editing in the abstract, but I can see that major English editing is required, so I will not proceed with it in this detail throughout the manuscript.
• I strongly doubt that you can resolve any crustal information with this station setup, as you have virtually no crossing raypaths in the shallow parts. The residuals will instead smear from crust into the mantle and vice-versa. Teleseismic tomography simply doesn’t work for the crust, unless you have station distances of 5 km or so. In fact, you need to use a crustal correction. I cannot see that you have applied a crustal correction. Unless I have missed it (which i doubt), you need to apply such a crustal correction in your model.
• Please add some “hitpoint” maps and profiles (same depths and locations as for the checkerboard tests). These will basically show the number of raypaths in each model cell.
• Please also add a crustal layer in your checkerboard test. This should illustrate that crustal correction is needed.

L15: just “teleseismic tomography”, without “the”

L16: use “the FMM”, later in tis line “for every(?) iteration” (if that sounds right)

L17-18: You already mentioned that you are using “teleseismic tomography”. Perhaps say: “using this approach …”

L18: No need to say “teleseismic tomographic results”. Just “results” or “tomographic results” will do.

L19: “suggest” not “suggested”. Past would imply that the results are not suggesting it anymore.

L20: Again, not past (exhibited), this would mean that these anomalies have disappeared (as the last data were acquired in 2019, I think it’s safe to say that the geology has not substantially changed since then). “were found” is right, as you did your analysis in the past.

L22: again, use present: “mainly represent”, but perhaps it’s safer to say “can be correlated to…”?

L24: “We found” is again right.

L26: “It was further inferred” could be used, but you can also say “it is further inferred”

L27: “was found” doesn’t really fit here. Perhaps “is located…”

L27: General question (and also the anomalies described before): At which depths? It would have majorly different tectonic implications whether you find an anomaly in the lithosphere, asthenosphere or MTZ.

L29: “was speculated” – I suggest using “we speculate” or “we suggest” or “it is suggested”, or similar.

L30: “is a remnant” (change to present tense), also it should be “this paper conjectures”. I think you haven’t introduced PSCS.

L38: So what does PSCS exactly stand for?

L40: What is SCS?

L43-44: Change structure of sentence: A serpentine suite of rocks (do you mean serpentinites?) have been identified in …

L88: How is the magnitude minimising the lower mantle and core-mantle boundary effects (I guess that’s what you mean by nucleus)? There should be no connection. Larger mag, better s-n ratio. The teleseismic epicentral distance is avoiding complex ray-paths and of course the shadow-zone.

L93: OK, but only one station compared to hundreds of others will not make a huge difference. But on the other hand, it is quite important for the China Sea. What about longer recording times? How many stations did previous studies use? 393?

Fig. 2b: According to this figure, you are using events <30 deg epicentral distance. This must be discussed. Usually, for teleseismic events you can only use 30-90 deg.

Fig 4: Please add captions and details for the figures. What is shown in each of the panels?

L138: I think the absolutely basic principle is that it is assumed that the seismic wave at your array arrives at the same tie (as it is a relatively local/regional array). All travel time residuals at the stations are then assumed to be only caused by the local anomalies.

I will stop here, because I think a crustal correction is required for the tomographic approach on this scale and I couldn’t see/read where or if you applied it. No crustal correction will propagate crustal anomalies (including Moho depth variations) into the mantle. In your checkerboard tests you should add a reverse anomaly in the upper layers (perhaps 0-30 km), representing the crust. Then you will see how intense the smearing is. But for now I say you need to apply a crustal correction.

Author Response

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Round 2

Reviewer 3 Report

Sorry,

I cannot recommend this study to be published as it is.

Of course you cannot say anything about the crust in such a setup (as the authors agree) and almost no teleseismic tomography study does (for reasons).

Why the crustal correction is essential (even if you are not looking at the crust specifically) is that errors propagate through to the mantle and distort the image. You MUST apply it. Just saying that the crust is in average 30 km thick, and it would result in only minor travel time errors is not convincing. The area is complex with changes in crustal thickness of 10 km and more, which already results in travel time anomalies of several deciseconds. So either you need to proof that the crustal correction is not necessary (and by doing that you need to essentially calculate it once) or you need to apply it.

You need the crustal layer in the checkerboard tests, again, not to show that you can or cannot image things in the crust, but it will show you that and how much you will distort your deeper image by delay time anomalies propagating through into the mantle.

For a good reason most teleseismic tomography models are cut off at 50 or 100 km and ALL need to apply a crustal correction.

I cannot suggest publication without these additional elements.

Author Response

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Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.