Ionospheric effects of earthquakes on GPS data

Difficulties in identification of ionosphere precursors caused by seismic effects on the background of space-
temporary variability of the ionosphere, especially during electromagnetic perturbations, are the basic object
of criticism at use of the ionosphere as a foreshock detector. Variations of electronic density of the ionospheres
interpreted as ionosphere precursors of strong earthquakes, have the same order of size, and sometimes even
it is less in amplitude, than the variations connected with usual variability of the ionosphere. The intensive
researches of seismoionospheric relations within the last several years show that those seismoionospheric phe-
nomena are unique among a set of other reasons of ionosphere variability. Difference of physical mechanisms of
seismoionospheric relations from the mechanisms of ionospheric storm and other sources of ionosphere variabil-
ity lead to their various manifestation in ionospheric variations. The ionosphere perturbation associated with
lithospheric processes, is much more accessible for detection and registration by space radiophysical methods.
Until recently there were no standard techniques of detection ionosphere effects caused by seismic processes,
according to satellite navigating systems. It is necessary to note especially, that the account of all parameters
of ionosphere precursor allows to allocate it on the background of ionosphere variations caused by other effects,
that favourably distinguishes it from plasma and electromagnetic variations of other type offered as precursors
as they can be observed in the result of influences of other factors. The obtained results allow to confirm that
ionospheric foreshocks are really existing phenomena, and the developed techniques of their detection give an
opportunity of their practical use in the systems of warning and short-term forecast of catastrophic earthquakes.