Abstract
In this paper we investigate the ionospheric turbulence from observations of TEC variations as well as from VLF/LF transmitter signal observations before and during the disastrous seismic activity of August and October 2016 in Central Italy. The Total Electron Content (TEC) data of 8 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analysed using Discrete Fourier Analysis in order to investigate the TEC variations. The data acquired for VLF/LF signal observations are from the receiver of Thessaloniki (40.59N, 22,78E), Greece, which monitor the VLF/LF transmitters of the International Network for Frontier Research on Earthquake Precursors (INFREP). A method of normalization according to the distance between the receiver and the transmitter is applied on the above data and then they are processed by the Hilbert Huang Transform (HHT) to produce the corresponding spectra for visual analysis. The results of both methods indicate that the High- Frequency limit fo, of the ionospheric turbulence content, increases as the site and the moment of the earthquake occurrence is approaching, pointing to the earthquake locus.
Highlights
It is argued that tectonic activity during the earthquake preparation period produces anomalies at the ground level which propagate upwards in the troposphere as Acoustic or Standing gravity waves [Miyaki et al, 2002; Hayakawa et al, 2011; Hayakawa, 2011; Hayakawa et al, 2018]
In this paper we investigate the ionospheric turbulence from the observations of Total Electron Content (TEC) variations as well as from VLF/LF transmitter signal observations before and during the disastrous seismic activity of August and October 2016 in Central Italy
The produced disturbance starts to propagate in the ionosphere’s waveguide as gravity wave and the inherent frequencies of the acoustic or gravity wave can be traced on TEC variations (i.e. the frequencies between 0.003Hz and 0.0002Hz), which according to Molchanov et al [2004, 2006] correspond to the frequencies of the turbulent induced by the LAIC coupling process to the ionosphere
Summary
It is argued that tectonic activity during the earthquake preparation period produces anomalies at the ground level which propagate upwards in the troposphere as Acoustic or Standing gravity waves [Miyaki et al, 2002; Hayakawa et al, 2011; Hayakawa, 2011; Hayakawa et al, 2018]. The inherent frequencies of the acoustic or gravity wave range between 0.003Hz (period ≈ 5min) and 0.0002Hz (period ≈ 100min)), which according to Molchanov et al [2004, 2006] correspond to the frequencies of the turbulent produced by tectonic activity during the earthquake preparation period. During this propagration the higher frequencies are progressively dumped. A method of normalization according to the distance between the receiver and the transmitter is applied on the above data and they are processed by the Hilbert Huang Transform (HHT) to produce the corresponding spectra for visual analysis
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