【摘要】 利用法国DEMETER卫星观测的电磁、等离子体等参量的观测数据分析了2008年3月21日新疆于田7.2级地震前离子温度(T_i)、离子密度(N_i)、甚低频(VLF)磁场等出现的异常变化.T_i分析显示震中区上空出现的突变信号在更大空间多次重复出现,作为地震异常的信度不高.通过多次重访轨道对比发现H~+离子密度整体变化形态一致,但夏秋季节的峰值变化幅度是冬春季节的1倍.通过把2008年的数据与2007年和2006年同期的重访轨道数据进行对比,发现2008年在于田地震前1个月左右N_i在峰值区呈现了显著增强的变化趋势,并一直持续到地震前,2008年2月以后的峰值幅度是其他两年同期的1倍多.对于磁场频谱数据,抽取了震中区域上空2000km范围内多个轨道的单频(400Hz)信息,并在研究区域统一纬度空间(0～60°N)进行了时间序列对比,结果发现地震前2日内震中区域上空400Hz谱密度增加了近一个数量级,反映空间存在明显的VLF电磁辐射现象.对于3月20日极低频段(ELF)三分量电磁场的矢量分析显示观测时段内存在一些左旋极化电磁信号,反映了空间电离层离子密度变化伴随ELF电磁辐射信息.综合分析认为,这次地震前各参量的变化过程与目前地震孕育及电离层耦合机理相吻合.更多还原

【Abstract】 Based on the observing data of electro-magnetic field and other plasma parameters on DEMETER satellite of France,the anomalous variations in ion temperature(T_i),ion density(N_i), Very Low Frequency(VLF)magnetic spectral values and so on were analyzed before Yutian 7.2 earthquake in Xinjiang.The analysis on Ti shows that the abrupt abnormal signals above epicentral area occur frequently in a much wider space,so they are with lower reliability as seismic precursors. Using revisited orbit method to compare the shapes of the density of H~+,it is found that all curves in a year are with consistent shape,but the peak amplitude in summer and autumn is 1 times of that in spring and winter.Compared the curves of N_i in 2008 with those in 2007 and 2006,apparent increases were exhibited at peak value regions in one month prior to Yutian earthquake with the amplitude rising to more than a magnitude relative to the other two years since February,and it continued to the earthquake occurrence.As for the magnetic spectrum data,orbits were selected in the distance of 2000 km and single frequency(400 Hz)values were extracted and arranged to a time series according to their record date and common latitude scale(0～60°N).The results show that during 2 days before the earthquake,the spectrum values at 400 Hz increased approximately by an order of magnitude,reflecting an obvious electro-magnetic emission occurred in ionosphere before the earthquake.It is illustrated after processing the three components of ELF electric and magnetic field on March 20 by vector analysis that,some left-rotated polarization electro-magnetic signals existing at the observing period reflect that the variation of ion density in ionosphere was accompanied by the emission of ELF electro-magnetic signals.Summing up,the variation process of these ionospheric parameters is consistent to the coupling mechanism of earthquake preparation and ionosphere at present.更多还原