A study for local disturbances of ionospheric TEC prior to strong earthquakes

Earthquakes are natural disasters with sudden and destructive effects that can cause large casualties and property damage within a short time. Therefore, researchers have paid considerable attention to the study of anomalies prior to earthquakes, especially strong ones. Using the global ionosphere map of total electron content (TEC), we attempted to identify local disturbances potentially associated with earthquakes by analyzing the daily accumulation of TEC anomalies. Based on a statistical study of 2707 M ≥ 6.0 earthquakes, it was found that positive and negative anomalies are obvious at 3 days and 7 days prior to earthquakes, respectively. The occurrence probability of seismo-ionospheric anomalies for 7.5 ≤ M < 8.0 earthquakes is slightly higher than that for earthquakes with magnitudes less than 7.5. The ratio of earthquakes with TEC precursors to the total number of analyzed cases varies with latitude, exhibiting a descending trend from low to mid and then to high latitudes. The analysis revealed that the region of seismo-ionospheric anomalies generally expands with increasing earthquake magnitude. The spatial distributions of positive and negative TEC anomalies differ between the geomagnetic Northern and Southern Hemispheres. These observational findings indicate that acoustic-gravity waves and perturbed electric fields may act as potential pathways in the lithosphere‒atmosphere‒ionosphere coupling process.