关键词: 极低频电磁台网, 电磁同震信号, 小波变换

Abstract: Seven times coseismic electromagnetic signals recorded at Jinggu Station and signals caused by two strong earthquakes recorded at several CSELF stations around Jinggu statio are studied. It is found that the variation of the EM filed is similar to the seismogram and the amplitude of the coseismic EM signal is much larger than the background signal generated by earth induction, and the intensity of the vertical magnetic field is about ten times as big as the horizontal electromagnetic field. For coseismic EM signals recorded at the same station, the relationship between the amplitude of electromagnetic field and the magnitude is basically linear in logarithmic domain. Meanwhile, it is also affected by focal depth and epicenter distance. For the same earthquake, the coseismic EM signals recorded by different stations, the larger the epicenter distance is, the later the signal appears and the longer the duration is. However, the signal amplitude is not only affected by the epicenter distance, but also related to the near-surface medium at the observation point. According to the wavelet analysis, the main frequency of electromagnetic co-seismic signal is between 1Hz and 2Hz. At the start of the co-seismic signal, there are high frequency components, and the high frequency gradually decreases with the increase of epicenter distance. Moreover, compared with electric field, magnetic field can record more abundant high-frequency information. When Ms6.6 earthquake occurred in Jinggu, the station near the epicenter recorded signals with a stronger peak shape than the co-seismic signal, which appeared at the beginning of the arrival of the seismic wave. It is speculated that it may be the direct signal of the electromagnetic radiation of the earthquake rupture caused by the piezomagnetic effect.

Key words: CSELF network, coseismic electromagnetic signals, wavelet trasform