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Article

Investigation of Precursors in VLF Subionospheric Signals Related to Strong Earthquakes (M > 7) in Western China and Possible Explanations

1
National Institute of Natural Hazards, Ministry of Emergency Management of China, Beijing 100085, China
2
Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
3
School of Electronic Information, Wuhan University, Wuhan 430072, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(21), 3563; https://doi.org/10.3390/rs12213563
Received: 21 October 2020 / Accepted: 28 October 2020 / Published: 30 October 2020
Earthquakes may disturb the lower ionosphere through various coupling mechanisms during their seismogenic and coseismic periods. The VLF signal radiated from ground-based transmitters is affected when it passes near the disturbed region above the seismogenic area, and this anomaly can be recorded by ground-based VLF receivers. In this paper, the seismic anomalies before two strong earthquakes (M > 7) that occurred in western China were detected using the ground-based observation of VLF signal; the possible reasons for the anomalies were discussed using full wave simulation. The amplitude of the VLF signals observed by the link between NOV, KHA transmitter, and VLF receivers at Ya’an and Tonghai show obvious anomaly by nighttime fluctuation analysis. The simulated results demonstrate that the anomalies could have been induced by ascending/descending of the bottom height of the ionosphere, caused by depletion/increase in D region electron density. The simulated result also illustrates that terminator time shift could have been induced by descending of the bottom boundary of the ionosphere, which is due to modal interference between different wave modes. View Full-Text
Keywords: precursory of strong earthquakes; VLF radio wave; nighttime fluctuation; seismic anomalies; ionospheric disturbance; full-wave model precursory of strong earthquakes; VLF radio wave; nighttime fluctuation; seismic anomalies; ionospheric disturbance; full-wave model
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MDPI and ACS Style

Zhao, S.; Shen, X.; Liao, L.; Zhima, Z.; Zhou, C.; Wang, Z.; Cui, J.; Lu, H. Investigation of Precursors in VLF Subionospheric Signals Related to Strong Earthquakes (M > 7) in Western China and Possible Explanations. Remote Sens. 2020, 12, 3563. https://doi.org/10.3390/rs12213563

AMA Style

Zhao S, Shen X, Liao L, Zhima Z, Zhou C, Wang Z, Cui J, Lu H. Investigation of Precursors in VLF Subionospheric Signals Related to Strong Earthquakes (M > 7) in Western China and Possible Explanations. Remote Sensing. 2020; 12(21):3563. https://doi.org/10.3390/rs12213563

Chicago/Turabian Style

Zhao, Shufan, Xuhui Shen, Li Liao, Zeren Zhima, Chen Zhou, Zhuangkai Wang, Jing Cui, and Hengxin Lu. 2020. "Investigation of Precursors in VLF Subionospheric Signals Related to Strong Earthquakes (M > 7) in Western China and Possible Explanations" Remote Sensing 12, no. 21: 3563. https://doi.org/10.3390/rs12213563

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