Analysis of sub-ionospheric transmitter signal behaviours above L'Aquila region

We analyze the sub-ionospheric transmitter signals observed above L'Aquila by the electric field ICE experiment onboard the DEMETER micro-satellite. We consider the variation of the intensity level of the DFY transmitter station (Germany) during the occurrence of the L'Aquila earthquakes on April, 06th, 2009. We review the major methods based on the investigation of the ICE dynamic spectrum and the role of the time and the frequency profiles. We show that the drop of the German transmitter signal occurs nearly one week before the L'Aquila earthquakes. The origin of the decrease in the VLF transmitter intensity level is probably due to a lithospheric generation mechanism which indirectly disturbs the ionosphere. We discuss the behavior of the VLF sub-ionospheric transmitter signal and the models which might explain the origin of the transmitter signal attenuation above seismic regions.