ANALYSIS TO THE CHARACTERISTIC OF THE MEDIUM TERM ANOMALIES IN GROUNDWATER LEVEL IN LONGFANG REGION BEFORE ZHANGBEI M6.2 EARTHQUAKE

The study on the variation in groundwater level of the 4 shallow wells in Langfang region before Zhangbei M6.2 earthquake indicates that the variation difference in water level of the 4 wells shows clearly medium and short term anomalies.Their common character is increasing with positive value,decreasing,negative value,and then earthquake.We believe,as a additional force source,water level of shallow well acts on the crustal rock in form of fluid loading,pore pressure and chemical erosion,which promotes the Zhangbei earthquake.