Abstract: Soil gas concentration measurement can reveal fracture location and activity characteristics. In terms of the problem of unobvious surface exposure of the Xinzheng—Taikang NW concealed fault in Henan as well as the phenomenon of the macroscopic anomaly of underground escaping gas in May 2016, an NE—NNE geochemical observation cross-section about 13 km long was set near the west of Taikang, which is vertical to the direction of the fault, and it is used to analyze the relationship between the surface exposure location of concealed fault and the macroscopic anomaly of underground liberated gas. The observation results show that the anomalous section of the cross-section dovetails with the surface exposure location of the fault zone speculated by the shallow seismic prospecting in this area. The concentration anomaly of Rn, H₂ and CO₂ indicates that there are four faults on the south side and two faults on the north side, which reveals all the faults exhibit a characteristic of high angle. The CO₂ concentration anomaly in the south part is consistent with the macroscopic anomaly of the underground liberated gas, which should be considered as non-structural cause.

Key words: Soil gas concentration, Geochemistry, Shallow seismic prospecting, The Xinzheng—Taikang fault zone