Abstract: The underground fluid of Panjin No.1 well has been observed since 1973, which has not only enriched the means of observation, but also accumulated a large amount of observation data. The Panjin No.1 well has showed obvious abnormal changes before the several earthquakes, that provides an important reference for earthquake monitoring and prediction. In this paper, we studied the characteristics, prediction methods and mechanism of underground fluid anomalies in Panjin No.1 well. The analysis results that the anomaly characteristics and prediction methods of the underground fluid in Panjin No.1 well before earthquake indicate that, radon is mainly characterized by trend and impending anomalies, hydrogen is mainly characterized by short-term and imminent anomalies, which can use the threshold analysis, differential analysis and the critical slowing down methods to obtain a good results in identifying anomalies. Chloride ion is mainly characterized by short-term and imminent, which can use the original curve analysis method to have a good effect in extracting anomalies. The research results of the abnormal mechanism of underground fluid in Panjin No.1 well indicate that, there is a close relationship among the abnormal concentration of each measurement item, the strength of seismic activity and changes in regional stress field. Under the condition of regional compressive strain, the radon precursory anomalies in the Panjin No.1 well observation is characterized by increasing concentrations. Under a tensile strain state, the anomalies is characterized by V-shaped changes in radon concentrations.

Key words: The Panjin No.1 well of the Liaoning Province, Underground fluid, Abnormal characteristics, Prediction methods, Anomaly mechanisms