Abstract: Concentrations of radon and mercury in soil gas were measured with ED-3017 Radon Meter and Jm-4 Mercury Digital Meter respectively in the field in Lanzhou. The result shows: ① The anomaly behavior of radon and mercury in soil gas across the Liujiapu active fault is obvious. The mercury is better than radon in indicating the fault location. ② The typical anomaly pattern of radon and mercury concentration is the peak shape with low-higher-highest-higher-low values. ③ There are a group of high values i.e. more than two points cross the fault, whose concentration of radon and mercury is over two times higher than the background value. The locations along different segments of Liujiapu fault are determined according to the variation characteristics of radon and mercury concentrations. Meanwhile, the possibility for determining the characteristics and attitude of the fault based on the features pattern change of radon and mercury concentration is also discussed.

Key words: Active fault, Soil gas, Radon and mercury geochemistry