Abstract: Soil gas emission is closely related to tectonic and seismic activity and has been widely used to track active faults and monitor seismicity in the upper crust. Because active fault plays an important role as the channel of the earth's deep gas upward migration due to its high permeability and porosity, the geochemical characteristics of soil gas in fault zone is a good indicator of tectonic fracture and activity. In order to study the soil gas geochemical emission intensities and its correlation to fault activity, fluxes of Rn, Hg and CO₂ in soil gas and the ground resistivity were surveyed across the Yuxian-Guangling Fault and Kouquan Fault which are both Quaternary active faults in the border area of Shanxi Province, Hebei Province and Inner Mongolia Autonomous Region. In 2017, soil gas fluxes were measured in 2 profiles consisting of 10 and 9 wells of depth of 3.0m across the fault scarps in Yuxian-Guangling Fault and Kouquan Fault, respectively. Resistivity tomography sections were attained by ground resistivity survey with electrode spacing of 5.0m along the profiles of soil gas measurement. The gas geochemical data show that there exist two abnormal flux peaks across the Yuxian-Guangling Fault and one in the Kouquan Fault. The high density resistivity measurement shows that fault breccia and fractured rocks zones are developed under the measured faults, where higher values of soil gas flux are also observed. Fractures with high gas permeability in the strata favor the transfer and migration upward of soil gases, which results in the anomalies of gas flux value. In addition, the anomalies of gas flux values are spatially identical with the occurrence of the fault scarps. The soil gas degassing rate of Yuxian-Guangling Fault is higher than that of Kouquan Fault. The research results of high density electrical prospecting and previous tectonic activity show that low-resistance bodies are more developed and the fault activity is stronger with higher slip rate, which leads to the more intense emission of soil gas in Yuxian-Guangling Fault. The conclusions can be made that soil gas geochemical characteristics and degassing rate in fault zone is closely correlated to the tectonic activity and fracture degree. Combination of geochemical and geophysical methods is an efficient way for the monitoring and study of fault activity to estimate the possible earthquake hazards.

Key words: soil gas flux, high-density resistivity method, fault activity, fault structure, degassing rate

摘要： 断裂带气体的地球化学特征与断裂构造和活动性密切相关。文中结合地球物理和地球化学手段，研究了晋冀蒙交界区内活动性较强的蔚县-广灵断裂和口泉断裂的活动性。土壤气体Rn、Hg和CO₂的地球化学测量和高密度电法勘探结果表明，蔚县-广灵断裂上存在2处气体通量高值异常，口泉断裂有1处通量高值异常；2条断裂上通量高值处的下部，均发育有断裂和不同程度的岩石破碎。地下气体沿高渗透率破裂地层向上逸出到达地表，从而导致气体通量高值异常。高值异常空间分布与断裂带宽度和断层倾向具有很好的一致性。此外，蔚县-广灵断裂土壤气的脱气速率大于口泉断裂，这与高密度电法勘探和构造研究结果（蔚县-广灵断裂活动性更强）相符。研究结果为深入认识这2条断裂带的活动性和地震危险性提供了新的资料。

关键词: 气体通量, 高密度电法, 断裂活动性, 断裂构造, 脱气率