In recent years,soil gas has rapidly developed for wide application urban active fault detection because of its fast,convenient,high-efficiency,and low-cost characteristics.The measurement methods of Hg and Rn soil gases are established and are helpful for studying active fault detection and the hazard assessment.The focus of this research is determination of the position of the concealed fault and its occurrence to ultimately provide a target for further drilling and costeaning through analysis of the anomaly concentration characteristics of Rn and Hg gases in the soil.Due to the particularity of urban environmental conditions and the complexity of geological conditions to obtain more accurate and reliable results and thus better scientific analysis conclusions,it is necessary to conduct experimental research on the fault soil gas anomaly characteristics and influencing factors in the typical fields that have fault outcrops or drilling data prior to large-scale field detection and feature analysis.The goal of this project is to promote better control of geochemical exploration in Hezuo.The Hg and Rn soil gas concentrations were tested in two typical fault outcrops of Ganjia and Huangxiang gullies near Hezuo city,which is located in the western region of the northern rim of West Qinling. The results show that obvious anomalous concentrations of Hg and Rn gases exist in the fault zone,the peak of the concentration curve corresponds well to the fault location,and its curve can better reflect the nature and geometry of the fault.The results of six Rn and Hg measuring lines on two experimental sites indicate that the anomaly peak values are generally 1.5times higher than the background values and are grouped.In particular,the anomaly points are usually greater than twice the 1.5background value on the fault zone,and the curve exhibits the typical bow shape;the single abnormal point is considered to be the interference factor during observation.The Huang-Xiang gully on the west Qinling fault test site is the most typical,regardless of the instructions of abnormal points for the fault location or the response of the curve to the fault properties and geometric shape.In addition,Hezuo City is located in grassland.The surface is uniform,stable,low interferential and has beneficial vegetation cover.Therefore,it is desirable to detect the concealed fault by geochemical methods of soil gas and to trace the spatial and temporal variation characteristics of known active faults.