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介绍了地震附近甚低频(VLF)电磁波信号强度统计分析结果。统计数据全部来自法国的DEMETER卫星(轨道高度700km,近太阳同步轨道),处理中采用了稳健的两步处理方法。第一步,利用所有的观测数据构建电磁辐射背景图,在给定条件和给定轨道位置对电场波动强度进行了统计描述。第二步,在第一步得到的电场波动强度的统计分布背景基础上,对地震附近的观测数据进行分析,研究由地震活动引起的电场波动强度的变化,评估它们在统计上的显著性。在整个分析过程中,我们总计使用了大于两年半的卫星观测数据,并对在此期间全球范围内发生的大约9000个震级大于或等于4.8的地震进行了统计分析。统计结果显示,在夜间时段,对于浅源地震(震源深度小于或等于40km),在震前0～4小时的短时间内,电场波动强度会有4～6dB的显著降低。
The statistical analysis results of signal intensity of very low frequency (VLF) electromagnetic waves near earthquakes are introduced. The statistics are all from France’s DEMETER satellite (orbital altitude 700 km, near-sun synchronous orbit), with robust two-step processing. In the first step, the background image of electromagnetic radiation is constructed using all the observed data and the intensity of the electric field is statistically described at a given condition and at a given orbital position. In the second step, based on the statistical distribution of the intensity of the electric field obtained in the first step, the observed data near the earthquake are analyzed to study the changes in the intensity of the electric field caused by the seismic activity and evaluate their statistical significance. Throughout the analysis, we used a total of more than two and a half years of satellite observations and conducted a statistical analysis of approximately 9000 earthquakes of magnitude 4.8 or greater that occurred throughout the world during this period. The statistical results show that at nighttime, the intensity of electric field fluctuates 4 ~ 6dB in the short time from 0 to 4 hours before the earthquake for shallow earthquakes (source depth less than or equal to 40km).