The daily variation of geomagnetic z component before and after zhangbei M6.2 earthquake

The daily variation of geomagnetic Z component before and after Zhangbei M 6.2 earthquake has been summed up and analyzed by relative observed Z component data at 17 geomagnetic stations in Hebei province and neighbouring provinces. It is considered that there may be many anomalies before a relatively strong earthquake. The reverse of the daily variation can be regarded as mid term and short term anomaly. After that daily variation low point appears, when the boundary line continuously appear in an area, the earthquake might enter the short term and imminent stage. The extreme value area of the daily variation reverse and the continuously converging area of low point shift may be the future epicenter. Trace prediction made for many anomalies occurred before earthquake may obtain a better prediction effectiveness.