Abstract
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.
Highlights
The electromagnetic effects associated with earthquakes have been discussed for a long time
We present an analysis of the electric field disturbances in the extremely low frequency (ELF) range registered by DEMETER over the Abruzzi region prior to the April 6, 2009, L’Aquila earthquake
We discuss the response of the ionospheric plasma for the disturbance that originated with high probability from the lithosphere
Summary
The electromagnetic effects associated with earthquakes have been discussed for a long time. We discuss the response of the ionospheric plasma for the disturbance that originated with high probability from the lithosphere The case of this April 6, 2009, earthquake in Abruzzi is an excellent example for this kind of study. The mechanism that could perturb the ionosphere during the preparation for an earthquake are related to the redistribution of charges at the Earth surface, the emission of radioactive gas (radon), and/or the propagation of acoustic gravity waves These mechanisms have been studied previously in the literature [see for example, Pulinets and Boyarchuk 2004, and references therein]. The waveform registered in this mode of operation allows wavelet, bispectral and statistical analysis to be performed, which are relevant to a study of the properties of the observed disturbances of the ionospheric plasma (see Section 3) over the Abruzzi region. This allows the performing of wave propagation analysis [Santolík et al 2003]
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