Abstract: The detection of urban active faults is one of the main goals in city developments. Accor ding to the mechanism of fault gases such as radon and mercury gases formed above faults, the authors analyzed the radon and mercury gases anomaly characteristics above active faults. The analyses had been made on these characteristics above these faults of the soil radon and mercury gases anomaly based on two known faults in Changchun. The fault locations and their occurrences can be determined and the fault scales can be predicted by these characteristics. The authors discussed the influences of super cover layer properties on abnormal form. These conclusions provided a useful reference for urban active faults surveying and evaluation.

Key words: active fault, fault gas, soil radon measurement, soil mercury gases measurement