Analysis of observations backing up the existence of VLF and ionospheric TEC anomalies before the Mw6.1 earthquake in Greece, January 26, 2014



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Sánchez Dulcet, Francisco and Rodríguez Bouza, Marta and Silva, H. G. and Herraiz Sarachaga, Miguel and Bezzeghoud, M. and Biagi, P. F. (2015) Analysis of observations backing up the existence of VLF and ionospheric TEC anomalies before the Mw6.1 earthquake in Greece, January 26, 2014. Physics and chemistry of the earth, 85-86 . pp. 150-166. ISSN 1474-7065

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The present work integrates ground-based ionosphere measurements using very-low-frequency radio transmissions with satellite measurements of the total electron content to draw common conclusions about the possible impact that the Mw6.1 earthquake that took place in Greece on January 26, 2014, had on the ionosphere. Very-low-frequency radio signals reveal the existence of an ~4-day anomaly in the wavelet spectra of the signals received inside the earthquake preparation zone and a significant increase in the normalized variance of the signals prior to the earthquake (approximately 1 day before). Through total electron content analysis, it was possible to identify a clear anomaly from 15:00 until 20:00 UT on the day before the earthquake that appears again on the day of the earthquake between 07:00 UT and 08:00 UT. The anomalous values reach TEC*Sigma ~4.36 and 3.11, respectively. Their spatial and temporal distributions give grounds to assume a possible link with the earthquake preparation. The geomagnetic, solar and weather conditions during the considered period are presented and taken into account. This work is an initial and original step towards a multi-parameter approach to the problem of the possible earthquake-related effects on the ionosphere joining observations made from both ground stations and satellites. A well-founded knowledge of these phenomena is clearly necessary before dealing with their application to earthquake prediction purposes.

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© 2015 Elsevier Ldt.
The Portuguese team acknowledges the support of the Portuguese Science and Technology Foundation (FCT) through the project Pest/OE/CTE/UI0078/2014 and the FCT/FEDER-COMPETE project EAC (PTDC/GEO-FIQ/4178/2012) FCOMP-01-0124-FEDER-029197. We are grateful to Samuel Bárias for the maintenance of the Portuguese radio antennas, to Elisa Cardoso for her help with wavelet theory, to Tommaso Maggipinto for instructing us on the MatLab® wavelet script and to Rui Salgado for the interpretation of the weather data. H.G.S is grateful to FCT for the postdoctoral fellowship SFRH/BPD/63880/2009 and to Calouste Gulbenkian Foundation (Portugal) for the award Estímulo à Criatividade e à Qualidade na Actividade de Investigação (2010). The Spanish team acknowledges the support of the Spanish Ministry of Economy and Competitiveness through the project CGL2014-62113-EXP. This work is part of the research activity of the Spanish Team “Grupo de Estudios Ionosféricos y Técnicas de Posicionamiento Satelital (GNSS)” financed by the Universidad Complutense de Madrid. The authors are very grateful to Luigi Ciraolo for his collaboration. They also want to thank the International GNSS Service, IGS, and EUREF Permanent Network (EPN) for providing the GNSS data; the World Data Center for Geomagnetism Kyoto for the Dst and Kp index values; and Intermagnet for the magnetic field data. AVVSO, the Russian Weather website and OMNIWeb Data Explorer from NASA, also provided very valuable data. Figures were drawn using the Generic Mapping Tools (Wessel and Smith, 1998). The final version of the article was prepared when M.H. was on sabbatical leave at the Abdus Salam International Centre for Theoretical Physics (Trieste, Italy) granted by the Spanish Ministry of Education, Culture and Sports. The authors are grateful to Dr. Kazimirowsky and two anonymous reviewers for their comments and suggestions, which improved the quality of the present manuscript.

Uncontrolled Keywords:Lithosphere-atmosphere-ionosphere coupling; Earthquake precursors; Very-low-frequency radio transmissions; TEC anomaly
Subjects:Sciences > Physics > Geophysics
ID Code:35670
Deposited On:12 Feb 2016 14:52
Last Modified:05 Apr 2022 07:14

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