Investigating the Mechanisms of Earthquake-Induced Groundwater Radon Changes in a Hot Spring-Insight From Coupled Flow Rates, Water Temperature, and Radon Observation

Abstract

Radon (²²²Rn), a radioactive inert gas commonly found in the earth's crust, is sensitive to crustal strain. Radon monitoring is widely recognized as an effective method for earthquake precursor detection. However, the underlying physical mechanisms responsible for these anomalies have not been investigated quantitatively. Thus, in this study, changes in radon concentration were systematically analyzed by integrating flow rates and water temperature data from the Banglazhang #1 hot spring in Yunnan, China, following the 1996 Lijiang Mw 7.0 earthquake and the 2004 Sumatra Mw 9.1 earthquake, both of which induced significant hydrological responses. Our analysis demonstrated that meteorological factors were not the primary drivers of radon concentration changes. The change in the mixing ratio from different depths of water was identified as the primary mechanism driving radon concentration changes following the Lijiang earthquake. Furthermore, the release of radon from particle movement, along with the change in the mixing ratio after the earthquake, might explain the co-seismic response following the Sumatra earthquake. The water–rock interaction surface area increased from about 7 × 10⁴ m² to 1.85 × 10⁵ m² following the Sumatra earthquake. Our study showed that coupling of flow rates, water temperature, and radon could provide a robust explanation of the earthquake-induced hydrological response. Thus, monitoring multiple parameters is essential for accurately and promptly detecting earthquake-related signals.