RESEARCH ON FREQUENCY SPECTRUM CHARACTERISTICS OF VLF ELECTROMAGNETIC FIELD IN EARTHQUAKE IONOSPHERE
地震电离层VLF电磁场频谱特征研究

By analyzing the electromagnetic spectrum data observed by DEMETER satellite during the time interval between March 2006 and February 2009,it is found that the characteristics of electric field power spectrum of global ionosphere in DEMETER altitude are as follows:the 50-300 Hz frequency band about earthquake ionospheric effect are the dominant frequency the closer,the distance to seismic spatial position,the more significant seismic anomaly;indifferent hemispheres of the earthquake,abnormal azimuthal direction is different.The studies on the events in northern hemisphere in geomagnetic summer show that the anomaly corresponding marine quakes occured in geomagnetic summer the frequency spectrum anomaly of geomagnetic field basically were positive and these land negative and corresponding the quakes in different hemisphere were significantly different:these in the northern hemisphere were positive and meridional,and negative anomaly of north but negative anomaly opposite in the southern hemisphere,the negative anomaly were northeast and positive ones southwest.