Density of radon in atmosphere soared before Great Hanshin Earthquake


The density of radon in the atmosphere sharply increased before the Great Hanshin Earthquake devastated Kobe and surrounding areas in January 1995, researchers have said.

A group of researchers from the semi-governmental National Institute of Radiological Sciences (NIRS), Kobe Pharmaceutical University and other organizations say the discovery will help predict earthquakes in the future.

However, a University of Tokyo seismologist cautioned that the causal relationship between the rise in the density of radon in the atmosphere and earthquakes must be clearly proven before establishing an earthquake prediction system.

"It's been pointed out for many years that there is a causal relationship between radon and earthquakes, but questions remain over its proof," Prof. Katsuyuki Abe of the university's Earthquake Research Institute, said. "Even if it was deemed successful this time, it is necessary to prove the causal relationship and clarify its mechanism before concluding that it can be used to predict other quakes."

The group used data on the density of radon that Kobe Pharmaceutical University has monitored at its campus since January 1984 as part of its observations of natural radiation. The campus is located 25 kilometers northeast of the epicenter of the Great Hanshin Earthquake.

The group of researchers compared the average level of radon over a nine-year period until December 1993 and data shortly before the killer quake, and found that the density started to rise around September 1994. It reached twice the normal amount in December of that year.

The epicenter of the quake is covered with granite that contains a massive amount of radium and radon.

The researchers applied the data from September to December 1994 to a model of the condition of energy in the earth's crust before the quake struck, and concluded that the energy would be released between Jan. 13 and 27, 1995. The killer quake occurred on Jan. 17 of that year.

The group presumes that radon was released from cracks in granite around the epicenter caused by minor tremors prior to the Great Hanshin Earthquake. (Mainichi)

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January 17, 2007