Variations of equatorial electrojet as possible seismo-ionospheric precursor at the occurrence of TEC anomalies before strong earthquake

The measurements of GPS signal delays show that the local areas of increased/decreased Total Electron Content ( TEC) of the ionosphere can be observed before strong earthquakes. The main possible cause of these TEC disturbances is the vertical plasma drift under the action of zonal electric field. The spatial pattern of electric potentials for such electric field was proposed. The model calculations were done to investigate the efficiency of the proposed mechanism. The calculation results revealed the agreement with TEC variations observed before strong earthquakes and showed that the equatorial electrojet variations can be considered as precursors of earthquakes.