关键词: 地震预报, 地下流体, 前兆异常

Abstract: The Huailai No.4 well is one of the national key observation wells. Obvious anomalies have been observed in this well before the occurrence of many earthquakes. Therefore,the well has played an important role in the monitoring of earthquake activity in Northwest Beijing region. This paper describes in detail the anomalies of underground fluid in the well before the occurrences of 5 moderate-strong earthquakes. In addition,we have also collected the earthquake-reflecting anomalies of the underground fluid observed in the Huailai No.4 well before the occurrence of earthquakes of magnitude above 4.0 in Huailai and its neighboring area since 1998. The research shows that the Huailai No.4 well may sensitively reflect M≥4.0 earthquakes that occur within the range of ≤260km around the well. The main features of precursory anomalies of underground fluid observed in the Huailai No.4 well can be summarized as follows: ⑴ The precursory anomalies of water mercury appear as abrupt variations. They occur several days to 2 months before the occurrence of an earthquake. The amplitude of variation might be several to tens times as high as the background value. The higher the amplitude of anomalies the greater the magnitude of earthquake will be. The earthquakes occur after the ending of anomalies; ⑵ The precursory anomalies of carbon dioxide in fault gas appear as sharp variations at many points. They occur 16 days to 47 days before the occurrence of an earthquake. The amplitude of variation might be several times to ten times as high as the background value. The higher the amplitude of anomalies,the greater the magnitude of earthquake will be. The earthquakes occur when the anomalies fall off; ⑶ The precursory anomalies of water radon appear as stepped variation. They occur several days to 2 months before the occurrence of an earthquake. The amplitude of anomalies might be of about 15% of the background value. The earthquakes occur during the growing period of anomalies; ⑷ The precursory anomalies of hydrogen escaped from groundwater appear as abrupt variations. The amplitude of variation of anomalies might be 3 times as high as the background value. The earthquakes occur after the ending of anomalies. All these results may shed light on the earthquake-related behavior of the underground fluids in this well,and may enhance the capability of earthquake prediction in the near future.

Key words: earthquake prediction, underground fluids, precursory anomalies