The very low-frequency transmitter radio wave anomalies related to the 2010 Ms 7.1 Yushu earthquake observed by the DEMETER satellite and the possible mechanism
<p>Earthquakes may disturb the lower ionosphere through various coupling mechanisms during the seismogenic and coseismic periods. The VLF (very low-frequency) signal radiated from ground-based transmitters will be affected when it penetrates the disturbed ionosphere above the epicenter area, a...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-09-01
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| Series: | Annales Geophysicae |
| Online Access: | https://angeo.copernicus.org/articles/38/969/2020/angeo-38-969-2020.pdf |
| Summary: | <p>Earthquakes may disturb the lower ionosphere through
various coupling mechanisms during the seismogenic and coseismic periods.
The VLF (very low-frequency) signal radiated from ground-based transmitters will be affected when
it penetrates the disturbed ionosphere above the epicenter area, and this
anomaly can be recorded by low-Earth orbit satellites under certain
conditions. In this paper, the temporal and spatial variation of the signal-to-noise ratio (SNR) of the VLF transmitter signal in the ionosphere over
the epicenter of 2010 Yushu Ms 7.1 earthquake in China is analyzed using
DEMETER (Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions) satellite observation. The results show that SNR over the
epicenter of the Yushu earthquake especially in the southwestern region
decreased (or dropped) before the main shock, and a GPS–TEC (Global Positioning System; total electron content) anomaly
accompanied, which implies that the decrease in SNR might be caused by the enhancement of TEC. A full-wave method is used to study the mechanism of the
change in SNR before the earthquake. The simulated results show SNR does not always decrease before an earthquake. When the electron density in the lower
ionosphere increases by 3 times, the electric field will decrease about
2 dB, indicating that the disturbed-electric-field decrease of 20 % compared
with the original electric field and vice versa. It can be concluded that
the variation of electron density before earthquakes may be one of the
important factors influencing the variation of SNR.</p> |
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| ISSN: | 0992-7689 1432-0576 |