Analysis of geomagnetic anomalies before the Jianhe M5.5 earthquake

Daily variation ratio of geomagnetic vertical component （Z） is important in the study of earthquake precursor analysis. The ariation magnetic field makes an induced magnetic field because of the earth conductivity, and the induced magnetic field includes information from outer magnetic field and underground electrical conductivity, so the geomagnetic field Z component reflects more changes of underground activity than other components. The paper processes the geomagnetic vertical component data of partial geomagnetism of south China stations located in the study area by using the ratio of daily variation amplitude method. The results show here existed high value anomaly of load on December 22, 2014, and the earthquake occurred 99 days after the anomaly date. The double low point is the phase and amplitude change of the geomagnetic Z component, from the normal V-shape to the W-type. To change the normal diurnal pattern, 57 days before the earthquake, most regions such as Guizhou, Guangxi, Hainan, Hunan a double low anomalies. Near the epicenter is located in the low anomaly dividing line, the emergence of geomagnetic low-value displacement associated with earthquake gestation and occurrence. This paper combines daily ratio and double low point to predict earthquake, which can improve its credibility.