Abstract: By using the observational results of fault gas of Haihe fault, Cangdong fault, Tianjin north fault and Tianjin south fault in this paper, and by integrating with the survey results of artificial seismic method, the authors studied the problems of the relationship between anomalous site of soil radon and the depth of upper breaking point of fault, and the problem of the background field and background value. The results show that the overburden thickness has a certain influence to anomalous position of soil radon. In the area of the shallow overburden, the anomalies of soil gas radon are usual on the upper end of fault, and in the area of the thick overburden, the anomalous position of soil gas radon is not consistent with fault position. The anomalies position of soil gas radon deviates from the fault position at least 60m or so. In the aspect about the deviating distance and anomalous position, which is located in top wall or bottom wall of fault, we do not discover their statistical relation. In the aspect about the anomalous determination of soil gas, it is suitable by using the relatively high values of each profiles, rather than using the determination anomaly based on the background field.

Key words: Fault gas, Overburden, Background field and Background value, Anomaly of soil radon