Four ULF (0.01 Hz - 20 Hz) electromagnetic stations had been gradually established and put into service from 2010 to 2011 in Zhaotong area, Yunnan province. Two stations of Qiaojia and Yongshan have been running with ...Four ULF (0.01 Hz - 20 Hz) electromagnetic stations had been gradually established and put into service from 2010 to 2011 in Zhaotong area, Yunnan province. Two stations of Qiaojia and Yongshan have been running with continuous and high quality recordings and free of influence of solar activities, like magnetic storms. In this investigation, daily recordings from 1 January 2020 to 22 May 2021 have been examined of these both stations. The results show that weak anomalous signals appeared at the beginning of March 2021 with relative low magnitudes of 0.6 nT at Qiaojia station and 0.3 nT at Yongshan station. At the end of this month, the emissions gained an abrupt increase and the amplitudes reached up to 3.8 nT at Qiaojia station and 1.2 nT at Yongsha station. Then, the amplitude decreased to be 0.5 - 1.5 nT and 0.6 - 1.3 nT respectively at both stations but with a high variation frequency in all components. This situation lasted till the Yangbi </span><i><span style="font-family:Verdana;">M</span></i><sub><span style="font-family:Verdana;">S</span></sub><span style="font-family:Verdana;"> 6.4 earthquake happened on May 21, 2021, more than 300 km away from these two ULF observing stations. Totally, the ULF magnetic emissions had been characterized by a synchronous variation in all components at two observing stations.展开更多
文摘Four ULF (0.01 Hz - 20 Hz) electromagnetic stations had been gradually established and put into service from 2010 to 2011 in Zhaotong area, Yunnan province. Two stations of Qiaojia and Yongshan have been running with continuous and high quality recordings and free of influence of solar activities, like magnetic storms. In this investigation, daily recordings from 1 January 2020 to 22 May 2021 have been examined of these both stations. The results show that weak anomalous signals appeared at the beginning of March 2021 with relative low magnitudes of 0.6 nT at Qiaojia station and 0.3 nT at Yongshan station. At the end of this month, the emissions gained an abrupt increase and the amplitudes reached up to 3.8 nT at Qiaojia station and 1.2 nT at Yongsha station. Then, the amplitude decreased to be 0.5 - 1.5 nT and 0.6 - 1.3 nT respectively at both stations but with a high variation frequency in all components. This situation lasted till the Yangbi </span><i><span style="font-family:Verdana;">M</span></i><sub><span style="font-family:Verdana;">S</span></sub><span style="font-family:Verdana;"> 6.4 earthquake happened on May 21, 2021, more than 300 km away from these two ULF observing stations. Totally, the ULF magnetic emissions had been characterized by a synchronous variation in all components at two observing stations.
