Analysis of anomaly characteristics of the soil gas radon from the crossing fault in the mid-east area of Qilian mountain before the 2016 Menyuan Ms6.4 earthquake

Based on the mobile monitoring network of tectonic geochemical in the Mid-East section of Qilian mountain, the precursory anomaly analysis and seismic situation tracking in the seismic hazard area were carried out by monitoring the concentration of soil gas radon crossing fault and combining with the distribution characteristics of seismic activity b value. Results show that the concentration of radon released changed significantly difference in the Mid-East segment of Qilian mountain during 2007–2013, under the background of the regional stress field enhancement, the gas release concentration of Gulang fault significantly decline, implying there is an obvious squeezing and the fault stress accumulation resulting in the decrease of porosity and radon concentration, so we circle a potential over magnitude 6 earthquake hazard fault segment in the future. Subsequently the 2016 Menyuan Ms6.4 earthquake occurred in this hazard zone. Therefore, we believe that soil gas radon can be used as a tracer for regional fault tectonic activities and stress changes, and it is necessary to pay attention to the monitoring of cross-fault soil gas in earthquake precursor observation.