Statistical characteristics analysis on the relationship between radon anomalies and earthquakes in Yunnan region

This article is based on the summary report of Yunnan earthquake cases from 1976 to 2022. It sorts out 73 sets of earthquakes with M≥5.0 one by one, and extracts abnormal information of radon measurement items before earthquakes occur, then explores the characteristics of radon precursor anomalies. The results are as follows: 　　① There were water radon anomalies of 63 earthquake sets out of 73 before earthquake, with a total of 190 anomalies proposed. There were a large number of anomalies and a low rate of earthquake underreporting, indicating that water radon observation has a good monitoring capability for regional earthquakes. Compared to that, the proportion of gas radon anomalies is relatively low, as there were only 4 earthquake sets out of 39 gas radon anomalies before earthquake, totaling 5 items following a higher rate of earthquake underreporting. But measurement points with good basic conditions have a high repetition rate of gas radon anomalies, and the occurrence of anomalies corresponds well to earthquakes. Among the 5 accumulated radon anomalies in historical earthquake cases, 3 of them were observed by Gaoda well. 　　② The water radon anomalies in earthquakes with M≥5.0 are mainly anomalies within 6 months, accounting for 71% of the total anomalies, with anomalies within 3 months accounting for 49% of the total anomalies. Starting from the year before the 5.0−5.9 magnitude earthquake, the number of water radon anomalies in different stages increased significantly. One month before the earthquake, most anomalies showed a turning point and ended, with a decrease in the number of anomalies. There are not many earthquake cases with abnormal gas concentration, but all anomalies are within 6 months, of which 80% are within 3 months. 　　③ The spatial distribution of water radon anomalies is different before earthquakes of different magnitudes. The anomaly of water radon is dispersed in space when the time from the earthquake occurrence is greater than 6 months. Starting from 6 months before the earthquake occurred, the number of anomalies within 100 km of the epicenter gradually increased. Starting from 1 month before the earthquake occurred, most of the anomalies outside the 100 km range returned to normal, with anomalies mainly concentrated near the epicenter. This feature can provide reference for location tracking. Before earthquakes with a magnitude of 6.0 or above, more water radon anomalies appeared in areas far from the epicenter, which were relatively scattered. This may indicate that the widespread occurrence of anomalies transmitted information that the stress levels in the entire field were increasing. In this state, the likelihood of a major earthquake occurring is higher. There are relatively few cases of accumulated abnormal changes in radon gas, and the spatial distribution characteristics do not show significant changes. 　　④ Based on the summary report of earthquake cases, this article shows that there are more anomalies in water radon than in gas radon, and the prediction effect of water radon is better than that of gas radon. This result is consistent with the understanding reflected by the actual use of data by prediction analysts. Several possible main reasons are that the observation points of water radon are more focused on deep circulating hot spring water, which is more likely to reflect deep tectonic activity; the second difference is the different observation methods. Most observations of water radon are conducted through manual collection of water samples and testing, with relatively stable technology, while gas radon observation is mostly automated. The stability of the devices for extracting radon gas from water and collecting it in the observation devices has not been fully solved, and the technology from gas collection to automatic detection process is not yet mature. The efficiency and stability of degassing directly affect the observation quality of data; The third is that some observation points of gas radon extract the escaping gas from static water level wells, which is difficult to reflect information from deep Earth. 　　Overall, the differences in the effectiveness of water radon and gas radon data in earthquake prediction are caused by factors such as the location of measurement points and observation techniques. At present, the observation data of gas radon in Yunnan has not yet achieved the effect of water radon in earthquake prediction. However, gas radon observation has advantages that water radon does not have, such as higher automation, faster transmission, higher data sampling rates, and can achieve hourly or even minute sampling, greatly increasing the amount of information. Technology and intelligence are the main development directions of radon observation. With the continuous improvement of radon observation technology and the accumulation of observation experience, its ability to capture seismic anomaly information will also continue to improve.