ANALYSIS ON THE PRECURSORY ANOMALY VARIATION OF WELL WATER LEVEL AT ZHUANGSHI,NINGBO BEFORE EARTHQUAKES

The anomaly characteristics of well water level at Zhuangshi,Ningbo before three M S5.0 earthquakes in South Yellow Sea is summarized and analysed.The results show that there are more than half a year trend anomaly and variation of annual regular before M S5.0 earthquake in most cases and short imminent term precursors appear one month or two months before the earthquake,such as variation of water level solid tide,increase of wave amplitude of date tide range and leapfrog etc.The analysis has played an important role in earthquake prediction practice of Zhejiang Province.