Extremely low frequency plasma turbulence recorded by the DEMETER satellite in the ionosphere over the Abruzzi region prior to the April 6, 2009, L’Aquila earthquake

Overview & Synopsis

The present study analyzes the low frequency fluctuations of the magnetic and electric fields prior to the earthquake with magnitude M.6.3 on April 6, 2009, in the Abruzzi region in Italy. This includes the disturbances of the ionospheric electromagnetic field prior to the earthquake, starting two weeks before the event, with detailed analysis for the days of March 26, April 1, April 2, and April 4, as 11, 5, 4 and 2 days prior to the earthquake, when the effects observed were strongest. Special attention is given to the characteristics of the spectra of these variations and the search for nonlinear effects. This analysis is possible in the time intervals when the extremely low frequency waveform was transmitted. Although the mechanism of the energy transmission from the earthquake preparation zone to the ionosphere is not determined, it can be said that the ionospheric plasma is an unstable medium and that even a small perturbation can lead to variations in the electromagnetic field and plasma parameters. Some aspects of this are discussed in the present report. The observations by the DEMETER satellite that are discussed suggest the presence of plasma turbulence over an area above the Abruzzi earthquake that occurred on April 6, 2009. The characteristics of the observed disturbances are studied through wavelet and bispectral analysis, the tools that are most relevant to the analysis of plasma turbulence. Furthermore, some statistical features are also presented, including the probability distribution function, and the kurtosis and skewness recently introduced into studies of such turbulence.