Coal Mining Causing Earthquakes, Study Says

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Human-Caused Quakes

Coal mining isn't the only human activity that can trigger earthquakes.

Klose has identified more than 200 human-caused temblors, mostly in the past 60 years. "They were rare before World War II," he said.

Most were caused by mining, he said, but nearly a third came from reservoir construction.

Oil and gas production can also trigger earthquakes, he added.

Three of the biggest human-caused earthquakes of all time, he pointed out, occurred in Uzbekistan's Gazli natural gas field between 1976 and 1984 (map of Uzbekistan).

Each of the three had a magnitude greater than 6.8, and the largest had a magnitude of 7.3.

Human-triggered earthquakes are particularly dangerous, Klose said, if they occur in seismically inactive areas.

That's partly because people aren't prepared for them. But also, he said, "regions that are naturally inactive are very trigger-sensitive, because stress has built up over long periods of time."

Expensive Implications

Klose's presentation drew considerable attention from the assembled geophysicists, who wondered if there were ways to reduce the risk by altering mining practices.

"One way would be to find a way that doesn't reduce the water in the mine," Klose said.

But as far as he knows, mining engineers aren't examining this, because they are currently unaware of the earthquake risk.

The danger is also relevant to proposals to sequester carbon dioxide by injecting it into geologic formations deep underground where the gas cannot escape and contribute to global warming.

"That alters stress in the crust [too]," Klose said, adding that the risk of earthquakes should be taken into account in planning the locations of such facilities.

Basically, he said, "don't put the injection fields close to large cities."

The research could also have an impact on earthquake-insurance premiums, André Unger of the University of Waterloo, in Ontario, told National Geographic News by email.

The precise method by which premiums are calculated is a deeply guarded trade secret, but they appear to be based on a region's historical earthquake risk—"a purely statistical methodology," he said.

The new finding indicates that other factors are now at work, he said.

Furthermore, Unger noted that underground carbon sequestration might be a mixed blessing from insurance companies' points of view.

A carbon-sequestration plan could reduce the risk of some types of damage (such as from hurricanes, which some scientists say are being strengthened by global warming), while increasing the risk of others, like earthquakes.

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