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2008年5月12日汶川M_s8.0地震前后,距震中320 km甘肃陇南汉王地震台的地电阻率、大地电场、ELF电磁等多种观测手段捕捉到这次地震前后的异常信息.本文采用解析方法,着重探讨汶川8.0级地震前后观测到的电磁场变化特征,从电磁现象来探讨汶川M_s8.0地震发生前后,电磁场长、中、短、临期的异常特征和变化规律.自2003年以来甘东南地区及甘川交界发生4次5.0级以上地震,从空间上看,有从南北地震带中段的西北向西南方向移动的特点,强度逐渐增强,其中,文县5.0和两次岷县5.0级以上地震可以视为汶川8.0级地震的前震;从时间上分析,震前陇南汉王地震台观测到电磁场出现了长趋势变化和短临异常变化,其特征:①2003～2008年,ZD8B地电仪观测的N54°W、N85°E和N73°W测道地电阻率均显示出长趋势变化和短期变化;②视电阻率各向异性度‘S′’年变化率在有震年(异常年)是无震年(正常年)的两倍;③ELF电磁仪观测到了(0.5～39 Hz)频率段的电场、磁场在汶川8.0级地震及余震序列中异常变化分别比正常月份大1～5个数量级,并记录到电磁同震现象;④大地电场仪(ZD9A-Ⅱ)在汶川震前17个小时也记录到高频临震变化信息.
Before and after the Wenchuan M_s8.0 earthquake on May 12, 2008, the earthquakes, the earth electric field and the ELF electromagnetic of the Hanwang Seismic Station in Longnan, Gansu, 320 km long ago, captured the anomalous information before and after this earthquake. Method, the characteristics of electromagnetic field observed before and after the Wenchuan MS8.0 earthquake are discussed, and the characteristics of anomaly and variation of long, short, medium and long term electromagnetic fields before and after Wenchuan M_s8.0 earthquake are discussed from electromagnetic phenomena. There are four earthquakes of magnitude 5.0 and above occurred at the junction of southeast China and Ganchuan. From the perspective of space, there is the characteristic of moving from northwest to southwest in the middle section of the north-south seismic zone, and the intensity gradually increases. Among them, 5.0 in Wen County 5.0 and above 5.0 in Min County The earthquakes can be regarded as the foreshocks of the Wenchuan M8.0 earthquake. From the time analysis, the long-term and short-term anomalies of the electromagnetic field have been observed by the Hanwang Seismic Station in Longnan before the earthquake. The characteristics are as follows: ① From 2003 to 2008, N54 ° W, N85 ° E and N73 ° W geodesic resistivity show long-term and short-term changes; ② apparent resistivity anisotropy ’S’ annual rate of change in the earthquake years (abnormal years) is No shock (Normal year); ③The electric field in the frequency band (0.5 ~ 39 Hz) was observed by ELF electromagnetism. The abnormal changes of the magnetic field in Wenchuan M8.0 earthquake and aftershock sequence were respectively 1 ~ 5 orders of magnitude larger than the normal one, Electromagnetic co-seismic phenomena; ④ earth electric field instrument (ZD9A-Ⅱ) 17 hours before Wenchuan earthquake also recorded high-frequency changes in the information.