A spatial analysis of the ionospheric TEC anomalies prior to M7.0+ earthquakes during 2003-2014

In the present paper, by using the global navigation satellite system total electron content (GNSS TEC), we conducted a statistical study on the spatial distribution of the seismo-ionospheric precursors (SIPs) before the occurrence of 133 shallow earthquakes of magnitude M ⩾ 7.0 in the global area during 2003-2014. To exclude the effect of space weather and geomagnetic disturbance, we considered the variations in the geomagnetic Dst indices, Kp indices, and the F10.7 indices; the GNSS TEC over the regions of ±10° near the epicenters is then investigated, and the spatial distribution of ionospheric TEC anomalies 0-15 days before the earthquakes is reported for the first time. We also statistically analyzed and compared the counts of the TEC anomalies over the epicenters in the eastern, southern, western, and northern directions 0-15 days prior to the earthquakes. Results show that the maximum occurrence number of ionospheric TEC negative anomalies specially appears over the epicenters and the anomalous behaviors of the ionospheric TEC attenuate slightly with the distance to the epicenters. However, the ionospheric TEC positive anomalies in the western direction have the biggest chance of occurring. Finally, the spatial distribution characteristics of the observed SIPs are explained by the electric-field-coupling model.