Radon is a natural radioactive gas. You cannot see, hear, feel, or taste it. It comes from the minute amounts of uranium that occur naturally in all rocks and soils. According to the Health Protection Agency, radon gas disperses outdoors, so levels are generally very low and do not pose a health hazard.
“This change in radon gas in the air may help in predicting the future of earthquakes,” said one of the researchers.
Radon gas in the atmosphere is normally shown to increase or decrease, depending on the season. according to the study. The gas began showing strong changes in the air since 2008, and it suddenly increased from June to December 2010. Then, it drastically decreased for about three months before the Tohoku earthquake.
The group also analyzed the change of density in radon gas in the atmosphere prior to Hanshin earthquake in 1995, which showed an unusual increase and decrease change right before the earthquake.
Though there is a difference in the length of low-levels between the Hanshin earthquake and Tohoku earthquake, researchers believe the difference is due to “the scale of the quake.”
The group studied the density of radon gas from the ground level to the atmosphere within a 30-kilometer (around 18.6 miles) radius, analyzing the exhaust monitor data in the unsealed radioactive material at the research laboratory.
“The level of radon gas in the atmosphere can be monitored in facilities like universities and hospitals with indicators,” said Professor Hiroyuki Nagahama of Tohoku University. “If we can create the monitoring network to check the changes, it will be able to contribute in predicting the earthquakes in the future.”
More detailed research result will be presented at the academic conference of the Seismological Society of Japan on Oct. 12, 2011.