Lower Ionospheric variations during the intense tectonic activity in the broader area of Greece on October of 2020

<p>In this paper we investigate the Lower ionospheric variations from TEC observations during the intense seismic activity of October 2020 in the area of Greece (35<sup> o</sup> £ j £ 42<sup>o</sup> N, 19<sup> o</sup> £ l £ 29<sup>o</sup> E).  The Total Electron Content (TEC) data are been provided by the  Hermes GNSS Network managed by GNSS_QC, AUTH Greece, the HxGN/SmartNet-Greece of Metrica S.A, and the EUREF Network. These data were analysed using both, statistical analysis of TEC variations in order to detect uneven gross variations and Discrete Fourier Analysis in order to investigate the TEC turbulence. The results of this investigation indicate that the High- Frequency limit f<sub>o</sub> of the ionospheric turbulence content, increases as aproaching the occurrence time of the earthquake, pointing to the earthquake epicenter, in accordane to our previous investigations (Contadakis et al., 2009; Contadakis et al., 2012; Contadakis et al., 2015; Scordilis et al., 2020). We conclude that the LAIC mechanism through acoustic or gravity waves could explain this phenomenology. Thus, observing the frequency content of the ionospheric turbidity we observe a decrease of the higher limit of the turbitity frequency band, as a result of  the differential  frequency attenuation of the propagating wave. In addition, the statistical analysis shows an excess greater than  3σ from the mean TEC values one and seven days before the earthquake. Since no major disturbance of the geomagnetic field occured during these days, we conclude that we probably observed precursory Ionospheric variations in accordance to analogous findings from the variation of VH/VHF electromagnetic wave propagrations over strong earthquake areas (e.g. Biagi et al. 2019)  </p><p> </p><p>References</p><p> </p><p>Biagi and 11 co authors, The INFREP Network: Present Situation andRecent Results. Open Journal of Earthquake Research, vol.8, p. 101-115, 2019.</p><p>Contadakis, M.E., Arabelos, D.N., Asteriadis, G., Spatalas, S.D., Pikridas, C., TEC variations over the Mediterranean during the seismic activity period of the last quarter of 2005 in the area of Greece, Nat. Hazards and Earth Syst. Sci., 8, 1267-1276, 2008.</p><p>Contadakis, M.E., Arabelos, D.N., Asteriadis, G., Spatalas, S.D., Pikridas, C. TEC variations over Southern Europe before and during the M6.3 Abruzzo earthquake of 6<sup>th</sup> April 2009, Annals of Geophysics, vol. 55, iss. 1, p. 83-93, 2012.</p><p>Contadakis, M. E., Arabelos, D.N., Vergos, G., Spatalas, S. D., Scordilis, E.M., 2015,TEC variations over the Mediterranean before and during the strong earthquake (M = 6.5) of 12th October 2013 in Crete, Greece, Physics and Chemistry of the Earth, Volume 85, p. 9-16., 2015.</p><p>Scordilis E.M., Contadakis M.E, Vallianatos  F., Spatalas S., Lower Ionospheric turbulence variations during the intense tectonic activity in Eastern Aegean area, Annals of Geophysics, 63, 5, PA544, 2020</p>

Lower Ionospheric turbulence variations during the intense tectonic activity in Eastern Aegean area

This paper may be considered as an additional approval of the way the tectonic activity affects the lower Ionosphere. The results of our investigation, on the occasion of the recent East Aegean tectonic activity, indicate that the High - Frequency limit, fo, of the ionospheric turbulence content, increases as the site and the time of the earthquake occurrence is approaching, pointing to the earthquake location.We conclude that the Lithosphere Atmosphere Ionosphere Coupling (LAIC) mechanism through acoustic or gravity wave could explain this phenomenology, as a result of a the frequency differential damping of the propagating turbulent in the ionosphere. Proper use of this result may lead to a method of earthquake hazard mitigation using the byproducts of the Global Positioning Network (actually Total Electron Contain, TEC, estimations) which are available freely.

Variation of some planetary seismic hazard indices on the occasion of Lefkada, Greece, earthquake of 17 November, 2015

In this paper we investigate the variation of the tidal triggering effect efficiency, by means of the tidal seismicity compliance parameter p, and the lower Ionosphere variations, by means of the variation of the High-Frequency limit, fo, of the ionospheric turbulence content with the time and space proximity to the site of the earthquake occurrence as well as by the intensity variations of VLF signals transmitted over the seismic area. It is shown that the “Earth tides-seismicity compliance parameter” p may be used as a medium time earthquake warning while the frequency content of the ionospheric turbulence over the earthquake epicenter, deduced directly from GPS network TEC observations or indirectly through the VLF transmission network, may be used for the short time earthquake forecasting, deserving the special attention of the authorities, the scientists and the society.

Ionospheric turbulence from TEC variations and VLF/LF transmitter signal observations before and during the destructive seismic activity of August and October 2016 in Central Italy

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.

Turbulence and Plasma Inhomogeneity Observed by Swarm Constellation

<p>The ionospheric environment is a complex system where dynamic phenomena, such as turbulence (fluid and magnetohydrodynamics) and plasma instabilities generally occur as a consequence of the coupling processes among solar wind, magnetosphere and ionosphere. It has been suggested that the turbulent character of the ionospheric plasma density also enters into the formation and dynamics of ionospheric inhomogeneities and irregularities, which essentially characterize the active equatorial, mid-latitude and polar regions. The ionospheric turbulence indirectly plays an important role also in the framework of space weather when due to the arrival of solar perturbations the plasma, the energetic particle distributions, the electric and magnetic fields within the magnetosphere and ionosphere are deeply modified thus paving the way for an increase in the ionospheric turbulence. Recent findings within the ESA funded project “Characterization of IoNospheric TurbulENce level by Swarm constellation (INTENS)” permitted us to investigate the role played by the turbulence on scales from hundreds of kilometers to a few kilometers in generating multi-scale plasma structures and inhomogeneities in the ionospheric environment at different latitudes. This presentation reports on the most promising results of the INTENS project regarding the investigation of turbulence and plasma conditions in the topside ionosphere using Swarm data.</p>

Lower Ionospheric turbulence variations during the intense seismic activity of the last half of 2019 in the broader Balkan region.

<p>In this paper, we investigate the ionospheric turbulence from TEC observations, before and during the intense seismic activity of September 2019 at Albania (main shock at l=19.445<sup>o</sup>E, j=41.372<sup>o</sup> N, M<sub>w</sub>=5.6)  and at Marmara sea (main shock at l=28.19 <sup>o</sup>E, j=40.872<sup>o</sup>N, M<sub>w</sub>=5.7), as well as of November 2019 at Albania (main shock at l=19.470<sup>o</sup>E, j=41.381<sup>o</sup>N, M<sub>w</sub>=6.4), and at Bosnia-Herzegovina (main shock at l=17.961<sup>o</sup>E, j=43.196<sup>o</sup>N, M<sub>w</sub>=5.4).</p><p>The Total Electron Content (TEC) data of 6 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 results of this investigation indicate that the High- Frequency limit f<sub>o</sub>, of the ionospheric turbulence content, increases by aproaching the site and  the time of the earthquake occurrence, pointing to the earthquake location (epicenter). We conclude that the LAIC mechanism, through acoustic or gravity wave, could explain this phenomenology. In addition the proximity of the tectonic active areas to the GPS stations offer us an opportunity to discriminate the origin of the disturbances</p>

Lower Ionospheric turbulence variations during the tectonic activity of the last quarter of 2019 in the Hellenic Arc (Greece)

<p>In this paper we investigate the ionospheric turbulence from TEC observations before and during the tectonic activity of the last quarter of 2019 in the Hellenic Arc, Greece (main shock at l=23.26<sup>o</sup>E, j=35.69<sup>o</sup>N, M<sub>w</sub>=6.1). The Total Electron Content (TEC) data of 6 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 results of this investigation indicate that the High- Frequency limit f<sub>o</sub>, of the ionospheric turbulence content, increases by aproaching the site and the time of the earthquake occurrence, pointing to the earthquake location (epicenter). We conclude that the LAIC mechanism through acoustic or gravity wave could explain this phenomenology.</p>

Lower Ionospheric Turbulence Variations During the Recent Activity of Etna’s Volcano, Sicily, in December 2018

In this paper, we present an investigation on the ionospheric turbulence from TEC observations before and during the recent activity of Etna’s Volcano. Mount Etna is located close to the eastern coast of Sicily. The last eruption of Etna volcano took place on 24 December 2018 while two days later (26 December, 02:19 UTC) an earthquake of M=5.0 occurred ~15 km to the ESE of the volcano, causing damage to the nearby city of Catania. The results of our investigation, on the occasion of the Etna’s Volcanic activity, indicate that the high-frequency limit fo of the ionospheric turbulence band content, is increasing with time to the volcano eruption while, at the same time, fo isdecreasing with distance from the volcano. We conclude that the LAIC mechanism through acoustic or gravity waves could explain this phenomenology, as it has happened in cases of earthquake activity. Our observations indicate that the effect of volcanic eruption on the band content of the ionospheric turbulence is insignificant at distances greater than 1000km (at the most), a fact that we must consider in our research on Ionospheric turbulence in relation to earthquake precursors research.