the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Simulation of a lithosphere-atmosphere-ionosphere electromagnetic coupling prior to the Wenchuan MS8.0 earthquake
Abstract. Continuously to a previous work on qualitatively investigating the probable electromagnetic interacting process among lithosphere, atmosphere and ionosphere, this work aims to quantitatively establish an electromagnetic coupling model among these three spheres prior to the Wenchuan earthquake. Firstly, a underground finite length electrical dipole in a half-space model has been employed to estimate the possible “energy source” for an observable 1.3 mV m-1 electrical field registered at 1440 km Gaobeidian station during the Wenchuan event. The result shows that the seismo-telluric current covers ~105–106 kA if the measuring frequency f = 0.01–10 Hz considered. The central magnitude of the vertical electrical field caused by the current at 0.01 Hz on the Earth’s surface can be up to kV m-1. Then, this vertical field acts as an input into an electric field penetration model. It is shown that this field attenuates quickly at the atmosphere and completely vanishes at the top ionosphere and produces a 0.1 mV m-1 additional electrical field at the ionospheric bottom. Through the TIE-GCM, this additional electrical field causes 0.01 % ionospheric variations on electron density and TEC near the Wenchuan epicenter, as well as near its magnetically conjugated point. Further, the simulations have also been discussively performed on frequencies of 1 Hz and 10 Hz. The results demonstrate that the variations of electron density present their maximum values at the height of ~300–400 km and the varied percentages of ionospheric parameters have been beyond 10 %, the same magnitude as what has been registered during the Wenchuan shock.
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RC1: 'Comment on nhess-2024-94', Anonymous Referee #1, 14 Aug 2024
The paper makes a significant effort to simulate the electromagnetic coupling through the lithosphere, atmosphere, and ionosphere before the Wenchuan MS8.0 earthquake. The integration of geophysical observations with advanced modeling techniques is a noteworthy approach. Nevertheless, there are several issues that require the author's attention to enhance the robustness of the study.
- In Section 2, the estimation of the current magnitude excited by the Wenchuan earthquake, derived solely from the seismic electromagnetic signals at the Gaobeidian station, may be overstated. The reliance on data from a single station may not provide a compelling argument; if the electromagnetic anomalies recorded at Gaobeidian are exceptional, closer stations should have reported stronger signals, yet such reports are absent. The authors should make some comments on this.
- The simulation's prediction of an induced electric field reaching up to 10^4 kV/m above the epicenter seems improbable. Is there any evidence from additional observational data or independent research supporting your simulation results?
- The authors are requested to elucidate the cause of the small high-potential anomaly observed at an altitude of 150-200 km above the source, as depicted in Figure 4.
- At lines 461-465, the authors should clarify why the results from Bortnik (2010) are considered comparable with the findings of this study.
Citation: https://doi.org/10.5194/nhess-2024-94-RC1 -
AC2: 'Reply on RC1', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC2-supplement.pdf
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AC5: 'Reply on RC1', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC5-supplement.pdf
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CC1: 'Comment on nhess-2024-94', Vincenzo Lapenna, 06 Sep 2024
The paper deals with an interesting and challenging topic: the study of the lithosphere-atmosphere-ionosphere electromagnetic coupling before the occurrence of large earthquakes. Starting from the analysis of the ULF electromagnetic emissions observed by the Hebei geophysical network before the occurrence of the great Wenchuan earthquake (Ms8), the authors evaluated the magnitude of an energy source capable of generating the ULF signals observed by the Hebei network. In a second step, they simulated the propagation of the electrical signals through the atmosphere and finally obtained an estimate of the energy at the bottom of the ionospheric layer.
The overall organisation of the paper is quite good, but I have to make some critical comments. The main comments are as follows:
- The estimate of the intensity of the "energy source" near the focus of the Wenchuan earthquake depends on the electromagnetic properties of the subsurface model (dielectric permittivity, magnetic permeability, conductivity). The assumption about the value of the conductivity could be better discussed, what are the changes if we modify the value of the conductivity? Furthermore, the assumption of a homogeneous half-space seems too simple, what are the possible changes introduced by a conductive shallow layer or by the presence of lateral discontinuities?
- The paragraph 3.1 could be revised and reorganised. The model introduced by Zhou et al. (2017) has been applied to study the coupling between ground-based electromagnetic emissions and the ionosphere, but there are only purely qualitative considerations about the like-steady conditions of the electromagnetic emissions.
- The equations and mathematical formulae in paragraph 3.1 could be better described and simplified. This would make the paper more readable.
- In the paragraphs "5. Discussion" and "6. Conclusions", the novelty of the results and their implications could be better emphasized.
Finally, there are some typewriting errors (see seismo-elluric) and some sentences that strongly require a re-formulation. An accurate revision of the English form is mandatory.
Citation: https://doi.org/10.5194/nhess-2024-94-CC1 -
AC7: 'Reply on CC1', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC7-supplement.pdf
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RC2: 'Comment on nhess-2024-94', Anonymous Referee #2, 21 Sep 2024
Dear authors and editor,
the manuscript "Simulation of a lithosphere-atmosphere-ionosphere electromagnetic coupling prior to the Wenchuan MS 8.0 earthquake" by
Mei Li, Zhuangkai Wang, Chen Zhou, Handong Tan, and Meng Cao is an interesting research devoted to modeling the propagation of electro-magnetic anomalies produced by pre- and coseismic processes associated with the occurrence of the large Mw 7.9-8.2 2008 Sichuan event.While the topic presents high scientific significance and the article is based on definitely good scientific research quality, I think that it suffers from a number of weaknesses preventing me to support its publication in NHESS if not after a major revision; however, the decision must go to the editor.
Below my major comments that I think should be addressed before the manuscript can be considered for publication:
1) The abstract should be a short, clear message summarising the content of the paper in a simple way that should be readable by non experts: addressed problem, state of the art, fundamentals of models, main idea, main result and its interpretation.
Simple, direct: a take home message. Authors' abstract does not go to the point, it is complex, I cannot understand what you did in your study just reading it.2) Several sentences in the main text are confusing, too long and contain language mistakes: I suggested several improvements in the attached pdf file to make the manuscript more enjoyable to readers.
3) Observations and simulations should not be confused: I think that a chapter devoted to show observations with maps etc should be added after the paragraphs devoted to models and then, discussions should be more focused on the comparison of models and actual observations. Quantitative analysis to understand if the model works appropriately should be done (e.g., misfit assessment etc).
4) It is not always clear which output of the model is compatible with physical phenomenons and which apparent signals are instead due to spurious effects, random fluctuations, computational instabilities (e.g., the red spot at the top of the two-peakes red anomaly in Figure 4 at about 180 km in height and 0 magnetic south-nord. Is it an artifact of the model?). Limits and hypotheses below the models should be sufficiently discussed.
Minor comments, discretionary requests, suggestions and corrections of minor mistakes are listed throughout the attached pdf file for the sake of simplicity.
Thanks for allowing me to review this work and for taking into account my humble comments.
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AC1: 'Reply on RC2', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC1-supplement.pdf
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AC4: 'Reply on RC2', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC4-supplement.pdf
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AC1: 'Reply on RC2', Mei Li, 11 Nov 2024
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RC3: 'Comment on nhess-2024-94', Anonymous Referee #3, 05 Nov 2024
Review of the manuscript
“Simulation of a lithosphere-atmosphere-ionosphere electromagnetic coupling prior to the Wenchuam Ms8.0 earthquake” by M. Li, Z. Wang, C. Zhou, and M. Cao
This manuscript deals with modelling of low-frequency electric fields and currents caused by an underground current element in the lithosphere, atmosphere and ionosphere. This model is used in order to explain electric perturbation of about 1.3 mV/m observed during the Wenchuan earthquake at Gaobeidian Station at a distance of 1.440 km from the epicenter of the earthquake.
The authors found that an underground source with a liner current of the order of 105 - 106 kA and a length of 150 km needs to produce this electric perturbation at such a great distance. The electric field on the earth’s surface, calculated from this model, was used as an input parameter for another model describing the penetration of an electric field through the atmosphere into the ionosphere. The perturbation of the electric field in the ionosphere was shown to decrease to a value of 0.1 mV/m, while the TEC variations should be 0.01%.
The authors focuses on the electric field produced by the underground electric current. Meanwhile, this current produces not only an electric but also a magnetic field. Away from the currents source, this magnetic field can be roughly estimated using Bio-Savart law:
B∼μ0IL/(4πr2).
where μ0 is the magnetic constant; I denotes the underground current; L stands for the length of the current; and r is the distance from the current element to the observation point.
Certainly, this law leaves out of account the influence of the boundary between the Earth and the ionosphere. Nevertheless, this law allows us to obtain an order-of-magnitude estimate. Substituting the author’s parameters: I = 1.5 105 - 3.4 106 kA and L = 150 km as well the distance r = 100 km into the above equation, we obtain that B=(0.23 - 5.1) 10-3 T; that is, a value of one or two orders of magnitude greater than the Earth’s magnetic field! At the distance r=1440 km (Wenchuan event) we obtain that B= (0.1 - 2.5) 10-5 T; that is, a value of the order of the Earth’s magnetic field. Such strong magnetic perturbations never observed both before and after seismic events!
It seems likely that such a fantastically big value of the underground electric current is unrealistic. This means that the authors model cannot explain either electrical field registered at 1440 km Gaobeidian station during the Wenchuan earthquake or the ionospheric effects possibly related to this earthquake.
It makes no sense to dwell on another disadvantages of this model, since the drawback noted above is fatal. That is why I recommend, unfortunately, to reject this manuscript.
Citation: https://doi.org/10.5194/nhess-2024-94-RC3 -
AC3: 'Reply on RC3', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC3-supplement.pdf
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AC6: 'Reply on RC3', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC6-supplement.pdf
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AC8: 'Reply on RC3', Mei Li, 11 Nov 2024
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2024-94/nhess-2024-94-AC8-supplement.pdf
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AC3: 'Reply on RC3', Mei Li, 11 Nov 2024
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