Analysis of seismic strain release related to the tidal  stress preceding the 2008 Wenchuan earthquake

Chen, Xuezhong; Li, Yane; Chen, Lijuan

doi:https://doi.org/10.5194/nhess-22-2543-2022

Articles | Volume 22, issue 8

https://doi.org/10.5194/nhess-22-2543-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/nhess-22-2543-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 8

Research article

|

09 Aug 2022

Research article |

| 09 Aug 2022

Analysis of seismic strain release related to the tidal stress preceding the 2008 Wenchuan earthquake

Xuezhong Chen, Yane Li, and Lijuan Chen

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Final revised paper (published on 09 Aug 2022)
Supplement to the final revised paper
Preprint (discussion started on 26 Jan 2022)

Interactive discussion

Status: closed

CC1:
'Comment on nhess-2021-405', Natarajan Venkatanathan, 07 Feb 2022

Dear Editor,
Herewith I have enclosed my comments on paper titled "Analysis of seismic strain releases related to tidal stress before the 2008 Wenchuan earthquake". Overall the authors have made observation that there is a seismic strain release, but the authors have to explain further why such behaviourial changes oberved between PEQs and NEQs.

Yours faithfully,
Venkatanathan

Citation: https://doi.org/10.5194/nhess-2021-405-CC1
- CC2:
  'Reply on CC1', Xuezhong Chen, 07 Feb 2022
  
  We thank Venkatanathan for the comments. Some researches reported the tidal triggering of earthquakes prior to moderate to large earthquakes (Tanaka et al., 2002b; Tanaka, 2010, 2012; Li et al., 2018). They investigated the tidal triggering of earthquakes in terms of event count. We investigated the tidal triggering of earthquakes before the Wenchuan earthquake in terms of seismic strain release,but not event count. Therefore the behaviourial changes oberved between PEQs and NEQs result from the tidal triggering of earthquakes prior to the Wenchuan earthquake indeed. The tidal triggering of earthquakes focus on the promoting effect of the tidal stresses, but our results reveal not only the promoting effect, but also the inhibiting effect of the tidal stresses. The increasing tidal stress will promote the occurrence of earthquakes, while the decreasing tidal stress will inhibit the occurrence of earthquakes when a large earthquake is impending.
  
  Citation: https://doi.org/10.5194/nhess-2021-405-CC2
  - CC3: 'Reply on CC2', Natarajan Venkatanathan, 07 Feb 2022
    
    Dear authors, I agree you have worked on seismic strain release. You have observed behaviourial changes of PEQs and NEQs , but there is no explanation that why NEQs decreases prior to the main event compared to the PEQs. You need to explain, when NEQs decreases due to decreasing tidal stress, then why PEQs increases.
    
    Venkatanathan
    
    Citation: https://doi.org/10.5194/nhess-2021-405-CC3
  - CC4: 'Reply on CC2', Natarajan Venkatanathan, 07 Feb 2022
    
    Dear authors, I agree you have worked on seismic strain release. You have observed behaviourial changes of PEQs and NEQs , but there is no explanation that why NEQs decreases prior to the main event compared to the PEQs. You need to explain, when NEQs decreases due to decreasing tidal stress, then why PEQs increases.
    
    Venkatanathan
    
    Citation: https://doi.org/10.5194/nhess-2021-405-CC4
    
    CC5: 'Reply on CC4', Xuezhong Chen, 07 Feb 2022
    
    The Earth tide produces cyclic stress variations in the Earth. These stress variations, of the order of 1000~10000 Pa, are far smaller than the tectonic stress. When the stress in the focal region is at lower values, the tidal stress can not influence the occurrence of earthquakes, but when it is close to a critical condition to release a large rupture, the tidal stress could take effect on the occurrence of earthquakes. The tidal stress increase will promote the occurrence of earthquakes, making the seismic strain release accelerate for PEQs (corresponding to the increase of k in Fig.4c), and when the tidal stress decrease will inhibit the occurrence of earthquakes, making the seismic strain release decelerate for NEQs (corresponding to the decrease of k in Fig.4c).
    
    Citation: https://doi.org/10.5194/nhess-2021-405-CC5
    
    CC6: 'Reply on CC5', Natarajan Venkatanathan, 07 Feb 2022
    
    Dear Author,
    Please include this explanation in the manuscript. For future studies - try to correlate PEQs and NEQs with dip (rake) of the fault.
    
    Citation: https://doi.org/10.5194/nhess-2021-405-CC6
    
    CC7: 'Reply on CC6', Xuezhong Chen, 08 Feb 2022
    
    Thank you for your comments and suggestions !We will do.
    
    Citation: https://doi.org/10.5194/nhess-2021-405-CC7
RC1:
'Comment on nhess-2021-405', Anonymous Referee #1, 09 Feb 2022

Dear Editor,

Herewith I have enclosed my comments on paper titled "Analysis of seismic strain releases related to tidal stress before the 2008 Wenchuan earthquake".

With warm regards,

Venkatanathan

Citation: https://doi.org/10.5194/nhess-2021-405-RC1
- CC8:
  'Reply on RC1', Xuezhong Chen, 09 Feb 2022
  
  The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-405/nhess-2021-405-CC8-supplement.pdf
  
  Citation: https://doi.org/10.5194/nhess-2021-405-CC8
  - AC1: 'Reply on RC2', Xuezhong Chen, 30 Mar 2022
    
    The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-405/nhess-2021-405-AC1-supplement.pdf
    
    Citation: https://doi.org/10.5194/nhess-2021-405-AC1
RC2:
'Comment on nhess-2021-405', Andrew Delorey, 25 Mar 2022

Comments for manuscript:

Analysis of seismic strain releases related to tidal stress before the 2008 Wenchuan earthquake

Xuezhong Chen et al.

The analysis shows results for PEQ (positive earthquakes) defined as when (delta)TCFS >0. Did you also do the analysis on PEQ defined as TCFS>0? If so, what were the results? Can you discuss how the choice of PEQ impacts your interpretation and the underlying physics? I think the observation is pretty robust, but there is a lot more analysis you could provide regarding your interpretation of the underlying physics and earthquake processes. As it stands, it is simply an interesting observation.

Can you resolve any changes in behavior with shorter time resolution? You average over 5-years. Is there any change in behavior that you can resolve within the period of time when R_k is increasing?

Why should k(neg) decrease when approaching the Wenchuan earthquake? It seems more intuitive that both k(pos) and k(neg) should increase, even if k(pos) increases faster.

There is another change in behavior around 1999, which can be seen in Figure 4a and 4c. Is there any explanation for that? Is it related to the change in instrumentation?

Figure 1b, what component of strain are you showing?

You write, “as the length of time with (delta)TCFS>0 is almost the same as that with (delta)TCFS<0”. What do you mean by almost? Do you account for the difference in your analysis? You should compare observed versus actual expected, not observed versus “almost” expected. This could impact your results.

There are some minor language problems, that could be fixed by having the manuscript reviewed by a more experienced English writer.

Citation: https://doi.org/10.5194/nhess-2021-405-RC2
- AC1: 'Reply on RC2', Xuezhong Chen, 30 Mar 2022
  
  The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-405/nhess-2021-405-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/nhess-2021-405-AC1

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Reconsider after major revisions (further review by editor and referees) (28 Apr 2022) by Oded Katz

AR by Xuezhong Chen on behalf of the Authors (28 May 2022) Author's response Manuscript

ED: Referee Nomination & Report Request started (01 Jun 2022) by Oded Katz

RR by Andrew Delorey (13 Jun 2022)

RR by Anonymous Referee #1 (07 Jul 2022)

ED: Publish subject to technical corrections (25 Jul 2022) by Oded Katz

AR by Xuezhong Chen on behalf of the Authors (27 Jul 2022) Author's response Manuscript

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Short summary

When the tectonic stress in the crust increases, the b value will decrease, meaning the effects of tidal stresses are enhanced gradually. Increase in the tidal Coulomb failure stress might promote the occurrence of earthquakes, whereas its decrease could have an opposite effect. This observation may provide an insight into the processes leading to the Wenchuan earthquake and its precursors.