Modification of sporadic E-layers caused by seismic activity

Among all earthquake precursors, those related to electromagnetic effects a re the most puzzling, and the many possible sources of noise are cause of l ively controversies. A large number of laboratory experiments clearly sugge st that micro-fracturing is associated with the appearance of spontaneous c harge production (electrification) and transient Electric or ElectroMagneti c (EM) Emission. Many electric and magnetic pre-seismic and co-seismic effe cts have been reported in the past as well as ionospheric perturbations. Th e aim of this paper is to review some of these ionospheric perturbations pe rformed in the former Soviet Union. The importance of sporadic E-layer form ation is underlined. Statistical studies with the available observations ar e done. At the end, a physical model of lithosphere-ionosphere coupling is presented in order to explain the observations. This model takes into accou nt the following effects at the Earth's surface: electric charge generation , emanation of radioactive gas, temperature variation, and surface vibratio n. It is shown that these effects can trigger sporadic E-layer formation.