Investigation of Pre-Earthquake Ionospheric Anomalies Using VLF/LF INFREP European and GNSS Global Networks

摘要

Ionospheric TEC ( Total Electron Content ) variations and Low Frequency (LF) signal amplitude data prior to three large earthquakes (M ≥ '> ≥ ≥ ge 6) in Greece were analyzed using observations from the Global Navigation Satellite System (GNSS) and the European INFREP ( International Network for Frontier Research on Earthquake Precursors ) networks respectively, aiming to detect potential ionospheric anomalies related to these events and describe their characteristics. For this, spectral analysis on TEC data and terminator time method on LF data were applied. It was found that TEC perturbations appeared few days (1-7) up to few hours before the events lasting around 2-3 hours, with periods 20 and 3-5 minutes which could be associated with the impending earthquakes. In addition, in all three events the sunrise terminator times were delayed approximately 20-40 min few days prior and during the earthquake day.