Correlation between the spatial distribution of radon anomalies and fault activity in the northern margin of West Qinling Fault Zone, Central China

Geochemical precursory characteristics of soil gas Rn, Hg, H2, and CO2 related to the 2019 Xiahe Ms5.7 earthquake across the northern margin of West Qinling fault zone, Central China

The Xiahe Ms5.7 earthquake occurred in Xiahe county, Gannan prefecture, China (35.10°N, 102.69°E) on October 28, 2019, with a source depth of 10 km. This study investigates the spatial and temporal evolution characteristics of cross-fault soil gas concentrations prior to the Xiahe Ms5.7 earthquake by analyzing Rn, Hg, H2, and CO₂ data collected from 11 profiles across the northern margin of the West Qinling fault zone from 2016 to 2019. The spatial distribution of these gases showed varying trends, with Rn concentration intensity decreasing from the Wushan segment to the east and west sections, while Hg, H₂, and CO₂ all broke the trend in the West Qinling fault zone's northern margin. The soil gas concentration intensity demonstrated a significant response to the Xiahe Ms5.7 earthquake, particularly in the west Ganjia sections. By integrating the seismogenic model and numerical simulation results, we explored the physical mechanism underlying these abnormal trends. Our findings suggest that the continuous decline characteristic of fault gas could be a valuable indicator of fracture tectonic activity, while an upward trend after continuous decline may signal a medium and short-term seismogenic event in the source area. These results provide a foundation for improved tracking of earthquake location and timing in a fault zone through cross-fault soil gas methods, highlighting the importance of enhancing deep fluid flow monitoring and seismogenic model research in fault zones.

Radon removal trap design and coefficient testing for the development of an effective radioxenon sampling, separation and measurement system

To monitor low-level radioxenon isotopes activity concentrations in the bulk gases, a radioxenon sampling, separation and measurement system has been developed. The xenon enrichment factor of this system is more than 10⁵ after the separation of impurities, including N₂, O₂, CO₂and H₂O, as well as radon and its progenies, such as ²¹⁴Pb and ²¹⁴Bi. Since radon and its progenies interfere with radioxenon measurement, they have to be removed before radioxenon counting. To separate radon from xenon, different dynamic adsorption coefficients of xenon and radon are used to design small radon removal trap to retain radon after eluting xenon, and the ratio between radon and xenon dynamic adsorption coefficient gives the adsorbent weight relationship between the xenon adsorption trap and its related radon removal trap. To test the effectiveness of radon removal, the relative measuring method is used by measuring γ-rays energies of radon progenies in canister filling with either the measuring sample prepared by the system or the original gas. The results show that the radon removal coefficient and the stable xenon recovery, which are two important parameters in the radioxenon system, are at the order of 10^-6 and >70% respectively. These meet the specifications proposed by the Comprehensive Nuclear-Test-Ban Treaty Organization.

Spatial distribution correlation of soil-gas radon (222Rn) and mercury with leveling deformation in northern margin fault zone of West Qinling, China

This study concerns measurement of ²²²Rn and mercury concentrations in soil-gas in the northern margin fault zone of West Qinling, Tibet (China). Based on profiles crossing perpendicularly the different segments of the fault at six different locations, the relations between the gas measurements, fault deformation, and seismic activity in each segment of the studied fault were analyzed, determining seismic risks in the fault zone. Soil-gas data are heterogeneous, but appear relatively organized along the three segments of the fault. The detailed multidisciplinary analysis reveals complex interactions between the structural setting, uprising fluids, leveling and seismic activity in different fault segments. The results for both fault soil gas and deformation indicated relatively stronger fault activity in the Wushan segment in the middle-eastern segment of the northern margin fault zone of West Qinling and lower activity in the Zhangxian segment, whereas the fault in the Tianshui segment was relatively locked. Additionally, in the Wushan strike-slip pull-apart area, the active influence of fluid activities facilitated the occurrence of small to medium-sized seismic events, which prevented the occurrence of larger events; in contrast, in the Tianshui segment, the west Zhangxian segment, the weak fluid activities and the corresponding strain rate will probably lead to strong earthquake buildup.