SNR changes of VLF radio signals detected onboard the DEMETER satellite and their possible relationship to the Wenchuan earthquake

Here we used the VLF signal data received by the DEMETER satellite, transmitted from various ground VLF transmitters which are located around China, to study the changes in the signal to noise ratio (SNR) before and after the Wenchuan earthquake, which had a magnitude of 8.0. We also found that the SNRs of different frequency signals decreased significantly over the epicenter region before the earthquake, and reverted to their original levels after the earthquake. This phenomenon may be related to the earthquake. Special Foundation of Basic Research from Institute of Geophysics, China Earthquake Administration (Grant No. DQJB08Z08), National Key Technology R & D Program (Grant No. 2008BAC35B01)