Attenuation of electromagnetic waves at the frequency approximately 1.7 kHz in the upper ionosphere observed by the DEMETER satellite in the vicinity of earthquakes

David Píša; Frantisek Nemec; Michel Parrot; Ondrej Santolik

doi:10.4401/ag-5276

Attenuation of electromagnetic waves at the frequency approximately 1.7 kHz in the upper ionosphere observed by the DEMETER satellite in the vicinity of earthquakes

David Píša ^{1, 2} Frantisek Nemec ² Michel Parrot ¹ Ondrej Santolik ^{3, 2}

1 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

2 Faculty of Mathematics and Physics [Praha/Prague]

3 IAP - Institute of Atmospheric Physics [Prague]

Abstract : The DEMETER satellite was the first satellite specifically dedicated to the recording of electromagnetic phenomena connected with seismic activity. Almost 6.5 years of measurements provide good opportunities to analyze a unique dataset with global Earth coverage. We present the results of a statistical study of the intensity of very low frequency electromagnetic waves recorded in the upper ionosphere. Robust two-step data processing has been used. The expected unperturbed distribution of the power spectral densities of electromagnetic emissions was calculated first. Then, the power spectral densities measured in the vicinities of earthquakes are compared with the unperturbed distribution and are examined for the presence of uncommon effects related to seismic activity. The statistical significance of the observed effects is evaluated. We confirm the previously reported results of a very small, but statistically significant, decrease in wave intensities a few hours before times of main shocks using this much larger dataset. The wave intensity decrease at a frequency of about 1.7 kHz is observed only during the night and only for shallow earthquakes. This can potentially be explained by increases in the cut-off frequency of the Earth ionosphere waveguide caused by imminent earthquakes.

Keywords : Surveys measurements and monitoring Waves and wave analysis Wave propagation

Type de document :

Article dans une revue

Annals of Geophysics, INGV, 2012, 55, 7 p. 157-163. 〈10.4401/ag-5276〉

Domaine :

Planète et Univers [physics]

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Attenuation of electromagnetic waves at the frequency approximately 1.7 kHz in the upper ionosphere observed by the DEMETER satellite in the vicinity of earthquakes

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Attenuation of electromagnetic waves at the frequency approximately 1.7 kHz in the upper ionosphere observed by the DEMETER satellite in the vicinity of earthquakes

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