Preseismic atmospheric radon anomaly associated with 2018 northern Osaka earthquake

Source: Science Daily

The concentration of the radioactive element radon is known to change in the ground before and after earthquakes. Previous studies have shown elevated radon levels in the atmosphere before the mainshock of a large inland earthquake due to foreshock activity and slow slip.

https://www.sciencedaily.com/releases/2021/04/210409104459.htm