Statistical Analysis of Response of Deep Well Radon Anomaly to Earthquake Activity

Abstract:

A lot of researches have shown that radon anomalies observed near fault zones are often related to crustal activities. However, the actual observation shows that this relationship is not clear. Sometimes no earthquake occurs when the gas radon anomaly appears, and sometimes no radon anomaly appears when earthquakes occur. Moreover, it is difficult to confirm whether the radon anomaly is caused by earthquakes.

The long-term observation station of the Chinese Continental Scientific Drilling Project (CCSD) is located at the junction of UHP metamorphic belt and Tanlu fault zone in eastern China. Based on the radon observation data during 2015~2019 in CCSD long-term observation station, we propose a new method to study the response of gas radon anomalies to earthquakes by analyzing the variation of probability density function (PDF) of gas radon anomaly data.

First, the gas radon observation data is converted to logarithmic domain. Then the daily variation component, annual variation component and the values related to air temperature and air pressure are removed by filtering and correlation analysis, so as to obtain the abnormal value of gas radon. Finally, the PDF of radon anomaly values are calculated by moving a fixed-length time window.

By analyzing the PDF variation of gas radon anomaly value, we confirm that the gas radon observation in CCSD has response to both near and far earthquakes. It is found that the gas radon anomaly caused by the earthquakes has a duration period (about 5 days), and earthquakes from different directions may cause different models of gas radon anomalies.

Based on the result above, we discuss the possibility of studying crustal activities by gas radon observation.