The terrestrial ionosphere above regions of seismic activity is considered on the data of Atmosphere Explorer -C satellite and on the data of ground based stations.
During preparation of earthquakes the modification of electron and ions concentrations and the variations of electron temperature as well as some heating of ionosphere were marked.
The analysis of long-time rows of critical frequencies foF2 at Pacific Ocean region (Kamchatka, Taiwan) has revealed the disturbance of correlation between the data of ionospheric stations, one of which is at seismic zone but other - out of it; some days before the earthquake or its forshock the correlation coefficients is fallen.
The revealed phenomena - the appearance of local anomalies and the disturbance of correlative dependence are the signs of earthquakes preparation.