Ionospheric TEC Monitoring Using Ground Based GNSS Observations for Earthquake Precursor Studies

Measurement of Ionospheric total electron content(TEC) for earthquake precursor studies has emerged as an innovative application of global navigation satellite systems(GNSS) which are gaining popularity. In present study we examine pre-earthquake Ionospheric anomalies with the aid of TEC measurement derived from ground based GNSS receivers. We did an experimental study considering data from two International GNSS Service (IGS) Stations VISO(in Sweden) and MDVJ (in Moscow) located relatively away from known earthquake regions. The data were processed using GPS-TEC for the period of 11 months. In most of the cases anomalies were found 5–10 days prior to earthquakes occurrences and were also studied vis-à-vis solar flares and geomagnetic storms activities to rule out its possible effects. Most importantly the study has critically analyzed epicentral distances of earthquakes from the GNSS location and it was found that anomalies have been detected at a larger distance from the earthquake epicenter as per the earthquake preparation zone defined by Liu(2004). Therefore, the study highlighted that the Ionospheric anomalies due to TEC perturbations in the Ionospheric detected at far off places from earthquake epicenter could provide non-ambiguous precursory signals attributed to earthquakes, thus reducing the chance of false alarms.