Application of Radon Isotopes to Study Variations in the Stress State of Rocks in Earthquake Prediction

The results of interpreting radon-220 (thoron) and radon-222 monitoring observations, carried out in 2002–2004 in the Northern Tien Shan are presented. The prognostic capabilities of thoron as a short-term earthquakes precursor are shown. It is noted that thoron anomalies are more contrasting compared to radon-222 anomalies. Insufficient contrast of radon-222 anomalies is explained by methodological errors during observations by seismic radon stations. Thoron behavior during the earthquake preparation process is consistent with the previously established spatiotemporal patterns for radon-222 (Kozlova et al., 2021). When using gases that are part of the subsurface atmosphere, radon isotopes are the most suitable for earthquake preparation process monitoring observations. The prospect of using other gases is limited by the absence of sources of their constant generation, the presence of a cumulative effect, and the complexity in detecting them. The above also applies to using variations in the contents of chemical compounds dissolved in groundwater for prognostic purposes.