Abstract: In order to study the geochemical characteristics of soil gas in the Zhuxia and Shangdan fault zones in the Qinling-Dabie orogenic belt, the field mobile measurement method was used to measure the soil gas Rn and CO₂ concentrations in three measuring lines of the two faults. The measurement results show that the concentrations of Rn and CO₂ in the three measuring lines vary in a wide range, among which the concentration of Rn in Shahedian measuring line varies from 3.31 to 128 kBq/m³, the concentration of CO₂ varies from 0.05% to 2.3%, and the concentration of Rn and CO₂ in Zhaojiazhuang measuring line range from 1.63 to 243.5 kBq/m³ and 0.06% to 1.26%, respectively. Which varies the largest range in the three measuring lines. The variation range of Rn concentration in Luoligou measuring line is 16.5~143 kBq/m³, and the variation range of CO₂ concentration is 0.17%~1.86%. Soil gas Rn and CO₂ have a clear indication of the fault location, especially the Shahedian and Zhaojiazhuang lines. By calculating the contrast of Rn anomalies of Shahedian line, Zhaojiazhuang line and Luoligou line, combined with the seismic activity in the area and the continuous observation data of hydrogen in the fixed point, it is preliminarily considered that the activity of Shangdan fault where Shahedian line and Luoligou line are located is weaker than that of Zhuxia fault where Zhaojiazhuang line is located.

Key words: Soil gas, Geochemical characteristics, Zhuxia fault zone, Shangdan fault zone