Coal Mining Causing Earthquakes, Study Says

Implications for CO2 Storage plans

Richard A. Lovett

for National Geographic News

January 3, 2007

The most damaging earthquake in Australia's history was caused by humans, new research says.

The magnitude-5.6 quake that struck Newcastle, in New South Wales, on December 28, 1989, killed 13 people, injured 160, and caused 3.5 billion U.S. dollars worth of damage (Australia map).

That quake was triggered by changes in tectonic forces caused by 200 years of underground coal mining, according to a study by Christian D. Klose of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York.

The quake wasn't enormous, but Australia isn't generally considered to be seismically active and the city's buildings weren't designed to withstand a temblor of that magnitude, Klose said.

All told, he added, the monetary damage done by the earthquake exceeded the total value of the coal extracted in the area.

Klose presented his findings at a meeting of the American Geophysical Union in San Francisco, California last month.

Heavy Burden

The removal of millions of tons of coal from the area caused much of the stress that triggered the Newcastle quake, Klose said. But even more significant was groundwater pumping needed to keep the mines from flooding. "For each ton of coal produced, 4.3 times more water was extracted," Klose said.

Other mining operations, he added, sometimes require as much as 150 tons of water to be removed for each ton of coal produced. "So this is on the low end," he said.

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 one-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, were a trio that 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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