The release of radon in active fault zones is a sustained radioactive pollution source of the atmospheric environment. The species, concentration and flux of radon emitted in soil gas in active fault zones in the Capital of China were investigated by in-situ field measurements. Two main species of radon discharging from soil gas in active fault zones were identified, including radon diffused and dispersed from permeable soil, and upwelling from faults. Higher concentrations and flux of radon from faults were observed in the Bohai Bay Basin due to the accumulated uranium in the sandstone reservoirs and higher permeability of the strata and bed rocks. Increased radon released by strong earthquakes persists, with the max flux of 334.56 mBq m⁻² s⁻¹ observed in FN (Fengnan district) located at the epicenter of the 28 July, 1976 Tangshan M_S 7.8 earthquake. The level of radon released in 8 of 22 locations within the Basin and Range Province (to the west of Taihangshan piedmont fault Zone) reached level 2, and 13 of 14 locations within the Bohai Bay Basin reached levels 2–4, according to the Chinese Code (GB 50325–2001, 2006). Corresponding protective and safety measures should be in place to protect the health of nearby residents, due to their exposure to radon emitted from the faults. Also, the concentration of radon in active fault zones should be investigated to assess the possible risk, before land-use is planned.

During the ongoing uplift and expansion of the southeastern margin of the Tibetan Plateau, the front edge of the Sichuan‐Yunnan rhombic block (SYB) has experienced intense tectonic activity and frequent seismicity. In this study, the fluid geochemistry in the primary active faults at the front edge of the SYB was investigated, with the aim of understanding the tectonic activity and intersection relationship between the Xiaojiang fault (XJF) and the Red River fault (RRF). Thermal spring water and gases exhibit a coupled spatial distribution relationship; relatively high ion concentrations and ³He/⁴He ratios (Rc/Ra ratios of 0.21 to 0.62Ra) are observed along the RRF, Qujiang fault (QJF), and Shiping‐Jianshui fault (SJF). Multidisciplinary research results have indicated that mantle‐derived intrusion has been detected in the crust beneath the QJF and SJF. The current tectonic activity in the front edge of the SYB remains intense, with compressive stresses shifting toward the western side of the XJF and accumulating on the QJF and SJF. This has led to the development of fractures, enhancing the water–rock interaction and deep‐derived gas degassing along the faults. The unmixing characteristics of fluids at the intersection area of these two faults suggest the absence of conduits for fluid migration between the faults. Owing to the lower gas ³He/⁴He ratios, lower shear strain rates, stable reservoir temperature field, and extremely low historical seismicity in the Indo‐Chinese block, it is speculated that the current movement of the XJF may not cut through the RRF and continue southward.

The concentrations, isotope ratios, and fluxes of CH₄and CO₂from mud volcanoes measured during a field survey on the southern margin of the Junggar Basin are reported. The origins and outputs of CH₄and CO₂from the four mud volcanoes are assessed, and the relationship between the characteristics of degassing and regional tectonics is discussed. The geochemical data indicate that thermogenic gases derived from the hydrocarbon reservoirs beneath anticlines could be the main source of the CH₄emitted from the mud volcanoes and that hydrocarbon degradation by microbes and carbonate decomposition could be the primary contributors to CO₂emissions from the soil in and around the mud volcanoes. Microseepage was the main mode of release for CH₄and CO₂from the mud volcanoes. The total CH₄output from the mud volcanoes was 147.83 ton/year, comparable to that from mud volcanoes elsewhere. The total output of CO₂from the mud volcanoes was 603.96 ton/year, which suggests that more attention should be paid to CO₂from mud volcanoes. The CH₄and CO₂outputs from the mud volcanoes, and from the Xihu fold in the four anticlines, decreased from south to north. This observation is consistent with the intensity of regional tectonic activity, which weakens from south to north. The results suggest that regional compression is the major triggering mechanism for CH₄and CO₂emissions from the mud volcanoes.

Tectonic controls on near-surface CH₄ and CO₂ concentrations were investigated by measuring CH₄ and CO₂ concentrations at the surface and a height of 1.5 m, in the different tectonic units that comprise the northwestern margin of Ordos Block, China, which has a complex tectonic structure and a history of strong earthquakes. CH₄ and CO₂ concentrations varied from 1905 to 2472 ppb and 397.5 to 458.5 ppm, respectively. Surface CH₄ and CO₂ concentrations were generally higher than those measured at 1.5 m, but showed similar trends, indicating that the measured CH₄ and CO₂ predominantly originated from underground gases. The CH₄ and CO₂ concentrations increased with an increasing strike-slip rate across the faults, and concentrations in the blocks with high internal deformation were much higher than those measured in the stable blocks. Regions of extensional deformation had higher gas concentrations than regions that had experienced compressional deformation. The spatial distribution of CH₄ and CO₂ at the study site had similar trends to faults associated with the Yinchuan Graben. The results of this study indicated that gas source, gas migration pathway, and tectonic stress were the main factors that influenced gas emission. The key factor is tectonic stress, which controlled the formation of tectonic structures, changed the pathway of degassing, and acted as the driving force for gas migration. The results of this study clarify the mechanism of CH₄ and CO₂ degassing in faulted regions and suggest that CH₄ and CO₂ concentrations may be useful precursors in the monitoring of seismic activity. The results may also help inform future assessments of the contribution of geological sources to greenhouse gas emissions.