Possible seismo-ionospheric anomalies associated with Mw > 5.0 earthquakes during 2000–2020 from GNSS TEC

The recent advances in space-based ionosphere measurements provide more detailed information about transient ionospheric anomalies associated with earthquakes (EQs). In this paper, we study the possible relation of EQs and ionospheric anomalies in a statistical analysis by analyzing 534 EQs of Mw > 5.0 during 2000–2020 from Vertical Total Electron Content (VTEC) acquired from the Global Navigation Satellite System (GNSS) of International GNSS Services (IGS) network. The selection criteria of these EQs was mainly subjected to two conditions: (1) at least three or more GNSS stations around the Dobrovolsky region were present, (2) the EQs occurred during quiet geomagnetic activity (Kp < 3, Dst ≥ -20nT). Particularly, we performed a statistical analysis on the basis of the median and interquartile range (IQR) over VTEC for each EQ, and the positive/negative anomalies were analyzed in the form of cumulative count for 20 days prior and after the mainshock day. Moreover, this study demonstrates that EQ induced VTEC anomalies occurred more frequently with 3 or more GNSS stations around the epicenter in Dobrovolsky’s region within a 5–10-day window before the EQs. Furthermore, the anomalies with a low deviation also initiated after the mainshock day within 5–10-day window. On the other hand, the deviations are more clear for Mw > 6.0 EQs, where positive anomalies were observed after excluding false anomalies in the corresponding IGS stations, showing a higher percentage of positive than negative anomalies and also more positive (negative) anomalies occur in solar maximum (minimum) years of the solar cycles 23 and 24. The false anomalies were the ionospheric perturbations associated with geomagnetic storms (Kp > 3) and VTEC values beyond upper/lower bounds outside the 5–10 days anomalous window. This statistical analysis assists to support the lithosphere and ionosphere coupling for future EQ ionospheric precursors.