Geochemical characteristics of radon in the soil of active faults in the northern Hainan region

In this study, we collected and organized observational data on soil radon concentrations from across seven active-fault monitoring lines in the northern Hainan region from 2020 to 2022. The average concentration, anomaly threshold, and number of measurement points exceeding the soil radon concentration threshold in the seven monitoring lines over this period were calculated, and the characteristics of the concentration changes in each monitoring line during the three years were analyzed. The results indicated that from 2020 to 2022, the concentration changes in soil radon emitted from the seven monitoring lines were consistent with the characteristics of soil radon concentration changes across active faults. Except for the 2020 Jinkang Road survey line, which had no measurement points exceeding the threshold, the observed values for the other survey lines exceeded the threshold every year. However, the magnitude of the exceedance was relatively small, as was the number of measurement points exceeding the threshold. The activity risk of the three active faults where the seven survey lines are located is not high, and the possibility of destructive earthquakes occurring is relatively small. This is the first study in which a spatiotemporal database of radon concentrations in the soil around active faults in the northern Hainan region has been established, and the background range of soil radon near active faults (8500～33000 Bq/m³) has been defined. Our findings provide a baseline reference for subsequent earthquake precursor identification.