Author(s)

Chuanfang Xiang¹, Mei Li², Zhaoli Ma¹, Chuanqi Teng³, Zhirong Li⁴, Zhigang Shao⁵

¹Yudong Earthquake Monitoring Station, Seismological Bureau of Zhaotong City, Zhaotong, China.
²China Earthquake Networks Center, China Earthquake Administration, Beijing, China.
³Qiaojia Seismological Bureau of Zhaotong City, Zhaotong, China.
⁴Earthquake Administration of Yunnan Province, Kunming, China.
⁵Institute of Earthquake Forecasting, China Earthquake Administration, Beijing, China.

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 M_S 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.

ULF Electromagnetic Emissions, Yangbi M 6.4 Earthquake, Synchronous Variation

Xiang, C. , Li, M. , Ma, Z. , Teng, C. , Li, Z. and Shao, Z. (2022) Ultra-Low Frequency Electromagnetic Emissions Registered during the 21 May 2021 Yangbi M_S 6.4 Earthquake in China. Natural Science, 14, 1-12. doi: 10.4236/ns.2022.141001.