'Helium levels in groundwater may predict earthquake risk'

Groundwater helium level could signal potential risk of earthquakes, according to researchers who discovered a relationship between levels of the noble gas and the amount of stress exerted on inner rock layers of Earth.
Scientists at the University of Tokyo in Japan hope the finding will lead to the development of a monitoring system which catches stress changes that could foreshadow a big earthquake.
Several studies, including some on the massive earthquake in Kobe, Japan, in 1995, have indicated that changes to the chemical makeup of groundwater may occur prior to earthquakes.
Researchers found that when stress exerted on Earth's crust was high, the levels of a helium isotope, helium-4, released in the groundwater was also high at sites near the epicentre of the 2016 Kumamoto earthquake, a magnitude 7.3 quake in southwestern Japan, which caused 50 fatalities and serious damage.

They used a submersible pump in deep wells to obtain groundwater samples at depths of 280 to 1,300 meters from seven locations in the fault zones surrounding the epicentre 11 days after the earthquake in April 2016.
They compared the changes of helium-4 levels from chemical analyses of these samples with those from identical analyses performed in 2010.

"After careful analysis and calculations, we concluded that the levels of helium-4 had increased in samples that were collected near the epicentre due to the gas released by the rock fractures," said lead author Yuji Sano, professor at the University of Tokyo.

Furthermore, scientists estimated the amount of helium released by the rocks through rock fracture experiments in the laboratory using rock samples that were collected from around the earthquake region.
They also calculated the amount of strain exerted at the sites for groundwater sample collection using satellite data.
Combined, the researchers found a positive correlation between helium amounts in groundwater and the stress exertion, in which helium content was higher in areas near the epicentre, while concentrations fell further away from the most intense seismic activity.
"More studies should be conducted to verify our correlation in other earthquake areas," said Sano.

"It is important to make on-site observations in studying earthquakes and other natural phenomena, as this approach provided us with invaluable insight in investigating the Kumamoto earthquake," he said.
The study appears in the journal Scientific Reports.