Anomalies of ULF Magnetic Field Variations Prior to the Jinggu M_S6.6 Earthquake

This study focus on ULF data before the Jinggu M_S6.6 earthquake on October 7, 2014 from three geomagnetic stations in Yunnan province:TongHai, JingGu, MengLa, analyze the Z component and H component of the data during the local nighttime period (LT=22h to 02h, UTC=15h to19h) at a particular frequency of 0.01~0.05 Hz. The result shows there seems no clear signature of Z component ULF radiation. However, the most significant fact shows that H component ULF signal raised before the earthquake, and depressed at occurrence moment of the earthquake, which suggests that the lower ionosphere was occurred before the earthquake.