Satellite study of VLF ground-based transmitter signals during seismic activity in Honshu Island

The paper is related to the study of the VLF (very low frequency) signal transmitted from the radio-navigation station in Komsomolsk-na-Amure at frequencies 11.9 kHz and 14.8 kHz during seismic activity in Japan. First, using data collected with the electric field experiment on board the DEMETER satellite, global maps of electromagnetic signal at the frequencies of the transmitter have been obtained. Second, particular analysis of the VLF signals have been done at the time of two powerful earthquakes which took place in the region of Honshu Island on 2005/08/16 and on 2007/07/16. Comparison with averaged background data revealed disturbances in the signal intensity transmitted from the Komsomolsk-na-Amure station and received by the satellite. Discussions to understand why such changes can be associated with seismic activity are developed.