Study on wave propagation of ELF emission anomaly before M_s8.0 Wenchuan earthquake

Based on the electromagnetic data recorded by DEMETER satellite during the past ten days before 12 May 2008 Wenchuan M_s8.0 earthquake, an anomaly below cut-off frequency is detected at the sixth day before the earthquake using power spectrum analysis. In order to learn the propogation characteristic of the abnormal electro-magnetic emmision, singular value decomposition (SVD) method is used to get polarization and wave vector of the emmison signals. The result shows that the anomaly reveals plane wave features and it propagated upwards. No similar phenomena are found above other non-seismic regions.