Preliminary Study On Ionospheric Phenomena Of The Wenchuan Earthquake Detected By The ICE Onboard The DEMETER Satellite

In recent years, as seismo-electromagnetic phenomena have been studied intensively, scientists have found that earthquake precursors exist not only in lithosphere, but also in atmosphere and ionosphere after some coupling. As satellites for earthquake were launched in many developed countries, more and more seismo-ionospheric coupling phenomena were reported. And more and more people focus on these phenomena.The electric field data from ICE onboard DEMETER satellite were used to analyze the anomaly existing in the region above earthquakes at satellite altitude. It is hoped that the possible seismo-ionospheric coupling can be explored by this way. In this thesis, the research developing status was summarized and the seismo-ionospheric coupling mechanism was briefly introduced firstly. And then the previous works about seismo-ionospheric coupling were reviewed, and the DEMETER satellite, the onboard instruments, the data and its application were presented. After that four different frequency signals transmitted from the VLF stations around china and recorded by the ICE(Instrument Champ Electrique) onboard DEMETER satellite flying across this region were choose. These signal data were extracted for analysis of the SNR (signal to noise ratio) distribution changes before and after the earthquake in the preparation zone. By analyzing the SNR distributions for pre- and post-earthquake above the earthquake preparation zone, we found that the SNR value decreases at the different frequencies one month before Wenchuan earthquake. The phenomenon may be caused by the seismo- ionospheric coupling during the earthquake preparation period. In addition, we also tried to use the grid method to locate and quantitate the abnormity. And we found the seasonal changes of SNR distribution. Finally, the work done in this thesis was summarized, and the inadequacies of the thesis and further works were proposed.