ABSTRACT
Disturbances in the ionosphere linked with seismic activity have been studied from a long time. Many results have been published on satellite observation of electromagnetic and ionospheric perturbations apparently associated with seismic activity (Parrot et al., 1993; Gokhberg et al., 1995; Hayakawa, 1997; Liperovsky et al., 2000). Probably the first results on local plasma density and temperature variations measured onboard AE-C and ISIS-2 satellites were published by Gokhberg et al. (1983). Boskova et al. (1993, 1994) had observed the changes in ion composition before earthquakes over the earthquake preparation zone. Afonin et al. (1999) analyzed a large database of plasma densities recorded in the 3000 orbits of Intercosmos-24. They reported a reliable correlation between the global distribution of seismic activity and ion density variations in the ionosphere, as measured by the normalized standard deviation (NSD) and the relative-normal standard deviation (RNSD). The statistical studies of Afonin et al. (2000) based on Cosmos-900 data and the results of Pulinets and Legenka (2003) had shown the existence of large-scale irregularities in the ionosphere several days or hours before strong earthquakes. Furthermore, significant contributions in the past have reflected on detection of ULF/ELF/VLF emissions at the time of earthquakes by low altitude satellites. Investigation of data by Intercosmos-24 satellite has revealed strong ELF/VLF perturbations associated with earthquakes (Molchanov et al., 1993). Parrot (1994) has performed statistical study of ELF/VLF emissions connected to electric and magnetic field by AUREOL 3 satellite and found increase in the emissions during earthquakes.
