New Insights into Earthquake Light: Rayleigh Scattering as the Source of Blue Hue and a Novel Co-Seismic Cloud Phenomenon

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments and Suggestions for the Authors:

This manuscript discusses the light flash produced by the Kaikoura earthquake in New Zealand and reviews multiple previous studies on earthquake-induced light flashes in other regions. The research is intriguing and demonstrates the authors' strong motivation to explore a challenging topic. The manuscript presents its content using innovative approaches and makes a strong overall impression. My overall recommendation for this manuscript is to publish in its current form. I have a few curiosities.

(1) Page 2, Lines 47 – 50

It may be better to move these sentences about RGB to the Method section or, alternatively, provide a more detailed explanation of RGB in that section rather than simply relocation the sentences.  

(2) Page 3, Figure3, Figure caption “Black horizontal bar”

 

It would be helpful to add more details about the "Black horizontal bar" in the caption. Another option is to illustrate the bar directly on the figure, such as by using an arrow to indicate it clearly.

(3) Figures 3, 4, 5, and 6, Figure captions

To maintain consistency with Figures 1 and 2, it may be better to add the date, time, and magnitude of the earthquake in the figure captions for Figures 3–6. For example:
“Sendai earthquake (Mw 7.4, 16.03.2022, 23:37 local time)”.

Additionally, the title displayed above the yellow line in the figures, "Sendai Aoba-ku," represents the city name (Sendai) and the district name (Aoba-ku). The earthquake occurred in Fukushima Prefecture.

A screenshot containing brief information about the earthquake from a web link is provided below.

(4) Page 6, Reference

Reference [20] is supposed to be missing. Please include it if necessary.

(5) Pages 6 – 8,  Method section, 2.1 The Kaikoura Earthquake” , Lines 141 – 179

There are two sections labeled 2.1: “2.1 The Kaikoura Earthquake” and “2.1 Archival Data”.
To resolve this duplication, consider moving “2.1 The Kaikoura Earthquake” (Lines 141–179) to the Result section, as it seems more appropriate there. This section may have been originally intended for inclusion in the Results section.

(6) Page 7, Figure 8 Axis titles

It may be better to add titles to both the vertical and horizontal axes for clarity.

(7) Page 8, Lines 205 – 213

These sentences discuss Rayleigh Scattering in light and the wavelength of scattered light. It may be more appropriate to move this explanation to the Introduction section.

Instead, the Methods section could include explanations about RGB and the color analysis method to enhance clarity and logical flow.

(8) Page 9, Reference

Reference [48] is supposed to be missing. Please include it if necessary.

(9) Page 9, Lines 229 “… of 11 years between   earthquake…“

The empty space between “between” and “earthquake” seems to indicate a year range. If so, it would be better to insert the specific years in the format “year–year” for clarity.

(10) Page 9, Table 1, Description of “Observer 4” and “Observer 5”

The “Description” in Table 1, for both “Observer 4” and “Observer 5” is supposed to be “Cloud flashes, Wainuiomata”.  Are there any differences between the descriptions for these two observers?

(11) Page 10, Line 250, “in the Figure”

The figure number is supposed to be missing after “Figure”. If so, please add the appropriate figure number.

(12) Page 10, Line 254, “…the seismic energy direction”

It may be better to insert additional explanations regarding the “seismic energy direction” in the text for better clarity and comprehension.

(13) Page 10, Figure 8, Axis titles

It may be better to add titles to both the vertical and horizontal axes for clarity.

(14) Page 14, Lines 310 – 311

It may be better to consider specifically indicating the two very bright white areas and the lower areas of blue light in the text or directly on Figure 14 using arrows, circles, or other visual markers for clarity.

(15) Page 14, Line 322 – 323, “0.590.27 s” and “1.5 s”

Although reference [8] is cited in the text, consider adding more explanations about the median and standard deviation of the time, as well as the timeframe of the cloud flashes, for better clarity.

(16) Page 14, Lines 325 – 326

It is better to explain the color analysis results using Figure 15 for better clarity and interpretation.

(17) Page 14, Figure 15 caption, Line 329 – 330

It would be helpful to explain how the plot was generated using RGB contributions obtained from Photoshop TM10 and the typical Rayleigh Scattering profile. This explanation could be included in the Methods section for better context.

(18) Page 16, Table 2, “Earthquake Date”

Consider adding “(Year)” below the “Earthquake Date” title in Table 2 to specify the format and improve clarity.

 

Curiosities:

1. Page 8, Lines 216 – 217

I am curious about the indication of “Detailed distribution of colors outward…”. How was the distribution of colors analyzed using PhotoshopTM? Additionally, how does this analysis help verify that the blue light is a result of Rayleigh Scattering?

2. Page 6, Mechanisms 1 and 3

Mechanisms 1 and 3 describe charge separation and induction, which are interesting theories. However, there is no clear connection between these mechanisms and the content in the Results and Discussion sections. The Discussion section presents fascinating hypotheses, some of which address charge and soil, which are related to the concepts in Mechanisms 1 and 3. However, these ideas don’t seem to directly correlate. Could you clarify how the Results and Discussion sections connect to Mechanisms 1 and 3? Did the results suggest any hypotheses related to charge separation or induction mechanisms?

Comments for author File: Comments.pdf

Author Response

Open Review (x) I would not like to sign my review report
( ) I would like to sign my review report Quality of English Language (x) The English is fine and does not require any improvement.
( ) The English could be improved to more clearly express the research.            

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	(x)	( )	( )	( )
Is the research design appropriate?	(x)	( )	( )	( )
Are the methods adequately described?	( )	( )	(x)	( )
Are the results clearly presented?	( )	(x)	( )	( )
Are the conclusions supported by the results?	( )	(x)	( )	( )

    Comments and Suggestions for Authors

Comments and Suggestions for the Authors:

This manuscript discusses the light flash produced by the Kaikoura earthquake in New Zealand and reviews multiple previous studies on earthquake-induced light flashes in other regions. The research is intriguing and demonstrates the authors' strong motivation to explore a challenging topic. The manuscript presents its content using innovative approaches and makes a strong overall impression. My overall recommendation for this manuscript is to publish in its current form. I have a few curiosities.

(1) Page 2, Lines 47 – 50

It may be better to move these sentences about RGB to the Method section or, alternatively, provide a more detailed explanation of RGB in that section rather than simply relocation the sentences.  Yes, both actioned

(2) Page 3, Figure3, Figure caption “Black horizontal bar”

 

It would be helpful to add more details about the "Black horizontal bar" in the caption. Another option is to illustrate the bar directly on the figure, such as by using an arrow to indicate it clearly. Yes; actioned.

(3) Figures 3, 4, 5, and 6, Figure captions

To maintain consistency with Figures 1 and 2, it may be better to add the date, time, and magnitude of the earthquake in the figure captions for Figures 3–6. For example:
“Sendai earthquake (Mw 7.4, 16.03.2022, 23:37 local time)”. Yes, this was done

Additionally, the title displayed above the yellow line in the figures, "Sendai Aoba-ku," represents the city name (Sendai) and the district name (Aoba-ku). The earthquake occurred in Fukushima Prefecture. Thanks for the information, which is now included; One extra reference (Xie et al ) now gives better context.

A screenshot containing brief information about the earthquake from a web link is provided below.

(4) Page 6, Reference

Reference [20] is supposed to be missing. Please include it if necessary. References now are complete.

(5) Pages 6 – 8,  Method section, 2.1 The Kaikoura Earthquake” , Lines 141 – 179

There are two sections labeled 2.1: “2.1 The Kaikoura Earthquake” and “2.1 Archival Data”.
To resolve this duplication, consider moving “2.1 The Kaikoura Earthquake” (Lines 141–179) to the Result section, as it seems more appropriate there. This section may have been originally intended for inclusion in the Results section. Section numbers have been regularised.

(6) Page 7, Figure 8 Axis titles

It may be better to add titles to both the vertical and horizontal axes for clarity. Done

(7) Page 8, Lines 205 – 213

These sentences discuss Rayleigh Scattering in light and the wavelength of scattered light. It may be more appropriate to move this explanation to the Introduction section. Yes, done.

Instead, the Methods section could include explanations about RGB and the color analysis method to enhance clarity and logical flow.  Much more explanation included.

(8) Page 9, Reference

Reference [48] is supposed to be missing. Please include it if necessary. Now complete.

(9) Page 9, Lines 229 “… of 11 years between   earthquake…“

The empty space between “between” and “earthquake” seems to indicate a year range. If so, it would be better to insert the specific years in the format “year–year” for clarity. Now we explain that the result does not need precision; it only indicates generally that the subject is common enough to allow research.

(10) Page 9, Table 1, Description of “Observer 4” and “Observer 5”

The “Description” in Table 1, for both “Observer 4” and “Observer 5” is supposed to be “Cloud flashes, Wainuiomata”.  Are there any differences between the descriptions for these two observers? A note is now included below the table.

(11) Page 10, Line 250, “in the Figure”

The figure number is supposed to be missing after “Figure”. If so, please add the appropriate figure number. Now regularised.

(12) Page 10, Line 254, “…the seismic energy direction”

It may be better to insert additional explanations regarding the “seismic energy direction” in the text for better clarity and comprehension. Yes; better explanation now included.

(13) Page 10, Figure 8, Axis titles

It may be better to add titles to both the vertical and horizontal axes for clarity. Done.

(14) Page 14, Lines 310 – 311

It may be better to consider specifically indicating the two very bright white areas and the lower areas of blue light in the text or directly on Figure 14 using arrows, circles, or other visual markers for clarity. Done

(15) Page 14, Line 322 – 323, “0.590.27 s” and “1.5 s”

Although reference [8] is cited in the text, consider adding more explanations about the median and standard deviation of the time, as well as the timeframe of the cloud flashes, for better clarity. Hopefully the clarity is improved.

(16) Page 14, Lines 325 – 326

It is better to explain the color analysis results using Figure 15 for better clarity and interpretation. Should now be better.

(17) Page 14, Figure 15 caption, Line 329 – 330

It would be helpful to explain how the plot was generated using RGB contributions obtained from Photoshop TM10 and the typical Rayleigh Scattering profile. This explanation could be included in the Methods section for better context. Done. Hope this is clearer.

(18) Page 16, Table 2, “Earthquake Date”

Consider adding “(Year)” below the “Earthquake Date” title in Table 2 to specify the format and improve clarity. Format improved.

 

Curiosities:

1. Page 8, Lines 216 – 217

I am curious about the indication of “Detailed distribution of colors outward…”. How was the distribution of colors analyzed using PhotoshopTM? Additionally, how does this analysis help verify that the blue light is a result of Rayleigh Scattering? This is explained now in more detail.

2. Page 6, Mechanisms 1 and 3

Mechanisms 1 and 3 describe charge separation and induction, which are interesting theories. However, there is no clear connection between these mechanisms and the content in the Results and Discussion sections. The Discussion section presents fascinating hypotheses, some of which address charge and soil, which are related to the concepts in Mechanisms 1 and 3. However, these ideas don’t seem to directly correlate. Could you clarify how the Results and Discussion sections connect to Mechanisms 1 and 3? Did the results suggest any hypotheses related to charge separation or induction mechanisms? The contribution of the paper to detailed mechanisms has to be preliminary and emphasise the paper's conclusions may not hold in other areas. For example our findings may apply to the surface but not to places deep underground. We now try to clarify this.

peer-review-44037622.v2.pdf Submission Date 20 January 2025 Date of this review 10 Feb 2025 01:25:29

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a compelling analysis of earthquake light (EQL) associated with the Kaikoura earthquake (Mw 7.8, 2016) and provides a summary of previous observations, theories, and mechanisms. The study effectively combines historical data, video analysis, interviews, and theoretical discussions to explore EQL. However, there are methodological gaps, logical inconsistencies, and missing clarifications that should be addressed. I have listed my comments, which if well-addressed will enhance the overall quality of the manuscript.

1. The title is somewhat vague. The term "New Explanations" is broad and does not clearly specify what aspect of earthquake light is being explained differently.
2. Lines 48-50: The use of Photoshop’s “eyedropper” tool to determine colors is questionable. A more robust method (e.g., spectrophotometric analysis) should be cited or used for accuracy.
3. Lines 75-77: The manuscript suggests that previous studies overemphasized igneous rocks for EQL, but does not cite recent literature discussing alternative lithologies (e.g., greywacke).
4. Lines 86-87: The statement that “many historical EQL observations were on igneous rock” could be misleading. It needs a systematic statistical breakdown of reported cases in different lithologies.
5. Lines 198-199: "Absence of storm lightning was confirmed using meteorological records." However, this does not rule out other optical atmospheric phenomena like Sprites or Airglow.
6. Lines 202-204: Using Adobe Premiere Elements to determine flash lengths introduces uncertainty. The frame rate of the original videos and camera calibration should be discussed.
7. Lines 229-230: The stated historical frequency of EQL (median 11 years in New Zealand) lacks proper statistical backing—were all earthquakes during this period analyzed, or only those with documented EQL?
8. Lines 298-299: The claim that rain was absent despite light clouds contradicts potential moisture effects on EQL mechanisms. How would you explain it?
9. Lines 325-330: Figure 15 lacks a statistical test to confirm if Rayleigh Scattering was the dominant process.
10. Lines 338-339: The manuscript states that Rayleigh Scattering explains blue colors, but does not address previous competing explanations (e.g., ionized nitrogen emissions).
11. Lines 348-358: The section on lithology lacks sufficient quantitative data—what percentage of known EQL observations are from greywacke regions compared to other rock types?
12. Lines 369-381: Table 2 on epicentral distances lacks statistical analysis—are the observed distances within expected ranges for seismic energy dissipation?
13. Lines 414-416: The study dismisses triboluminescence and charge induction too easily. These mechanisms might still contribute under certain conditions.
14. Lines 419-421: The Freund mechanism is preferred, but competing theories (e.g., stress-induced exoelectron emission) are not discussed.
15. Lines 427-432: The idea that cloud flashes might result from charge movement should be further explored. Are there past cases supporting this?

Author Response

Open Review (x) I would not like to sign my review report
( ) I would like to sign my review report Quality of English Language (x) The English is fine and does not require any improvement.
( ) The English could be improved to more clearly express the research.            

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	(x)	( )	( )	( )
Is the research design appropriate?	(x)	( )	( )	( )
Are the methods adequately described?	( )	(x)	( )	( )
Are the results clearly presented?	( )	(x)	( )	( )
Are the conclusions supported by the results?	(x)	( )	( )	( )

    Comments and Suggestions for Authors

The manuscript presents a compelling analysis of earthquake light (EQL) associated with the Kaikoura earthquake (Mw 7.8, 2016) and provides a summary of previous observations, theories, and mechanisms. The study effectively combines historical data, video analysis, interviews, and theoretical discussions to explore EQL. However, there are methodological gaps, logical inconsistencies, and missing clarifications that should be addressed. I have listed my comments, which if well-addressed will enhance the overall quality of the manuscript. Thanks for the positive comments and the careful work.

1. The title is somewhat vague. The term "New Explanations" is broad and does not clearly specify what aspect of earthquake light is being explained differently. This is quite correct. The title has been changed to emphasise the most important new findings. Other findings are included in the text but are mostly supportive rather than totally new.
2. Lines 48-50: The use of Photoshop’s “eyedropper” tool to determine colors is questionable. A more robust method (e.g., spectrophotometric analysis) should be cited or used for accuracy. Quite true but this has not been experimentally possible, so far. So the colour analysis via Photoshop is only about equivalent to making somewhat more objective the visual impression. No major point in the paper depends on high colour precision, and only the difference between sky-blue and turquoise is mentioned. (fig 3-7)
3. Lines 75-77: The manuscript suggests that previous studies overemphasized igneous rocks for EQL, but does not cite recent literature discussing alternative lithologies (e.g., greywacke). Some extra mention is now included.
4. Lines 86-87: The statement that “many historical EQL observations were on igneous rock” could be misleading. It needs a systematic statistical breakdown of reported cases in different lithologies. This is quite true, but needs a large study of its own beyond the scope of this paper. It would take, for example, the survey of Theriault, and find the rock types for each occurrence.
5. Lines 198-199: "Absence of storm lightning was confirmed using meteorological records." However, this does not rule out other optical atmospheric phenomena like Sprites or Airglow. These are now mentioned.
6. Lines 202-204: Using Adobe Premiere Elements to determine flash lengths introduces uncertainty. The frame rate of the original videos and camera calibration should be discussed. This is now discussed.
7. Lines 229-230: The stated historical frequency of EQL (median 11 years in New Zealand) lacks proper statistical backing—were all earthquakes during this period analyzed, or only those with documented EQL? A comment has been added. Full statistical treatment is not needed yet, because the only point was to show that earthquake light is a valid subject of research.
8. Lines 298-299: The claim that rain was absent despite light clouds contradicts potential moisture effects on EQL mechanisms. How would you explain it? This was not included because it is not clear whether water at or above the site of generation of earthquake light is important (our guess is that positive holes at high speed will travel faster through moist soils than through rock)
9. Lines 325-330: Figure 15 lacks a statistical test to confirm if Rayleigh Scattering was the dominant process. We now explain the difference to be tested is between Mie and Rayleigh scattering, and the difference even at first glance  is so huge that a statistical test is not needed.
10. Lines 338-339: The manuscript states that Rayleigh Scattering explains blue colors, but does not address previous competing explanations (e.g., ionized nitrogen emissions). The latter is mentioned, and may have some contribution under some circumstances.
11. Lines 348-358: The section on lithology lacks sufficient quantitative data—what percentage of known EQL observations are from greywacke regions compared to other rock types? Indeed, but this needs a paper to itself, and much work.
12. Lines 369-381: Table 2 on epicentral distances lacks statistical analysis—are the observed distances within expected ranges for seismic energy dissipation? The energy distribution is now mentioned but mainly as a rule-of-thumb; all cases in the table were experienced as locally strong earthquakes  even if far from the epicentre.
13. Lines 414-416: The study dismisses triboluminescence and charge induction too easily. These mechanisms might still contribute under certain conditions. Yes, and this caveat is now included.
14. Lines 419-421: The Freund mechanism is preferred, but competing theories (e.g., stress-induced exoelectron emission) are not discussed. We now discuss this briefly under the section on triboluminescence. Even if exoelectron speed is high it will not penetrate rock for large distances.
15. Lines 427-432: The idea that cloud flashes might result from charge movement should be further explored. Are there past cases supporting this? This is discussed, but only in an anecdotal, unreferenced form in Enomoto (2024) (Atmosphere 31: 916). Much research in the literature should seek accounts of the (very rare) ground to cloud lightning discharges, which may have accompanied an earthquake.

Submission Date 20 January 2025 Date of this review 08 Feb 2025 21:47:12

Reviewer 3 Report

Comments and Suggestions for Authors

Taking the earthquake that occurred in Kaikoura, New Zealand on November 14, 2016 as an example, this article provides an explanation of seismic light Based on the previous understanding of seismic light, the authors pointed out six aspects of research progress in seismic light, which have a promoting effect on the study of seismic light. But further modifications are needed.

Author Response

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	(x)	( )	( )	( )
Is the research design appropriate?	(x)	( )	( )	( )
Are the methods adequately described?	(x)	( )	( )	( )
Are the results clearly presented?	(x)	( )	( )	( )
Are the conclusions supported by the results?	(x)	( )	( )	( )

Comments and Suggestions for Authors

Taking the earthquake that occurred in Kaikoura, New Zealand on November 14, 2016 as an example, this article provides an explanation of seismic light Based on the previous understanding of seismic light, the authors pointed out six aspects of research progress in seismic light, which have a promoting effect on the study of seismic light. But further modifications are needed. We agree, and significant modification has been made. It became clear that further explanation of the Mie/Rayleigh scattering process was important. A few paragraphs were added. An improvement to the references resulted in a few references being added, and a few deleted, the overall change being a slight decrease. There were some large character-strings in the references for web-pages, which resulted in rather ugly formatting now regularised with left-justification. it was also found possible to improve table formating.

 

Submission Date

20 January 2025

Date of this review

10 Feb 2025 16:34:48

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have adequately addressed all my comments, and I am now satisfied with their revisions. However, the title still does not fully reflect the core findings of the work and remains somewhat ambiguous. I suggest adopting a clearer and more concise title. Based on my understanding, the authors may consider the following: 'New Insights into Earthquake Light: Rayleigh Scattering as the Source of Blue Hue and a Novel Coseismic Cloud Phenomenon.'

Author Response

The authors have adequately addressed all my comments, and I am now satisfied with their revisions. However, the title still does not fully reflect the core findings of the work and remains somewhat ambiguous. I suggest adopting a clearer and more concise title. Based on my understanding, the authors may consider the following: 'New Insights into Earthquake Light: Rayleigh Scattering as the Source of Blue Hue and a Novel Coseismic Cloud Phenomenon.'

With thanks to this reviewer; The manuscript now uses the suggested title, which is an improvement.

The changed file is attached.docx

Author Response File: Author Response.docx