Reduction of the VLF Signal Phase Noise Before Earthquakes

In this paper we analyse temporal variations of the phase a very low frequency (VLF) signal, used for lower ionosphere monitoring, in periods around four earthquakes (EQs) with magnitude greater than 4. We provide two analyses time and domains. First, evolution noise. And second, examine spectrum using Fast Fourier Transform (FFT) order to detect hydrodynamic wave excitations attenuations. This study follows previous investigation which indicated noise amplitude reduction, attenuations waves less one hour before considered EQ events as new potential ionospheric precursors earthquakes. ICV VLF transmitter signal emitted Italy recorded Serbia occurred on 3, 4 9 November 2010 are most intensive analysed study. The obtained results indicate similar changes amplitude, show an agreement acoustic excitations. However, properties attenuation characteristics different these parameters.