Analysis of Pre-Seismic Ionospheric Disturbances Prior to 2020 Croatian Earthquakes
Résumé
We study the sub-ionospheric VLF transmitter signals recorded by the Austrian Graz station in the year 2020. Those radio signals are known to propagate in the Earth-ionosphere waveguide between the ground and lower ionosphere. The Austrian Graz facility (geographic coordinates: 15.46 • E, 47.03 • N) can receive such sub-ionospheric transmitter signals, particularly those propagating above earthquake (EQ) regions in the southern part of Europe. We consider in this work the transmitter amplitude variations recorded a few weeks before the occurrence of two EQs in Croatia at a distance less than 200 km from Graz VLF facility. The selected EQs happened on 22 March 2020 and 29 December 2020, with magnitudes of M w 5.4 and M w 6.4, respectively, epicenters localized close to Zagreb (16.02 • E, 45.87 • N; 16.21 • E, 45.42 • N), and with focuses of depth smaller than 10 km. In our study we emphasize the anomaly fluctuations before/after the sunrise times, sunset times, and the cross-correlation of transmitter signals. We attempt to evaluate and to estimate the latitudinal and the longitudinal expansions of the ionospheric disturbances related to the seismic preparation areas.
Domaines
VolcanologieOrigine | Fichiers produits par l'(les) auteur(s) |
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