When towns to the east of Oklahoma City jiggled over the weekend with two of the state’s strongest-ever earthquakes, some people asked an obvious question: Does the recent expansion of “fracking” for natural gas in Oklahoma — shooting water and chemicals and sand into shale deposits to free trapped methane — account for the trembling ground?
Maybe. Oil and gas exploration has caused minor earthquakes in the U.S. since the ’30s, and a new report from Britain suggests that fracking itself can cause small quakes. It was “highly probable,” according to the report, that a drilling firm called Cuadrilla Resources caused two earthquakes near Blackpool, in northwest England, by fracking for shale gas in May.
But the British quakes were extremely mild — 2.3 and 1.4 magnitude — and experts argue that fracking, on its own, wouldn’t cause quakes much out of that range. (The weekend quakes in Oklahoma measured 4.7 and 5.6.) “It is extremely rare for fracking itself to cause detectable earthquakes,” writes Nicola Jones at Nature, “so rare that geologist Scott Ausbrooks of the Arkansas Geological Survey in Little Rock told this reporter in May that it never happens.”
Ausbrooks points out that a related activity does cause the earth to shake. Companies involved in mining, fracking, and oil exploration sometimes dispose of wastewater by pumping it into “injection wells,” and in the 1960s, the Rocky Mountain Arsenal, a U.S. Army site in Colorado, used injection wells to bury wastewater from chemical weapons. The Army shot a tainted solution of salty water more than 12,000 feet underground, which led to a flurry of quakes around Denver in the late ’60s. The largest were in the 4- and 5-magnitude range.
Fracking probably did cause a number of “micro quakes” in Oklahoma in January, according to seismic expert Austin Holland. The largest quake in that flurry measured 2.8. Holland says he doesn’t think fracking led to last weekend’s quakes. “It continues to be a possibility,” he told an Oklahoma news station, “but the connections are weak, and it would take much more research and a greater understanding of what’s going on in the sub-surface to begin to attribute this to oil and gas activities.”
Fracking, of course, is unpopular in some parts of the U.S. because poorly sealed wells have leached chemicals and methane into the surrounding groundwater. A flurry of Arkansas quakes raised a question about fracking there last year, but Ausbrooks said the shaking was probably related to injection wells, rather than fracking per se. The difference is important, because the nation’s shale-gas reserves could cut carbon emissions and free the country from its dependence on oil — if, and only if, the gas can be safely extracted.
Europe has been watching this U.S. debate. While France has outlawed fracking entirely, Germany is particularly anxious for new forms of energy, and it hopes to use natural gas as a “bridge” for its ambitious move away from nuclear power and toward renewable energy. It allows some limited fracking, but it plans to buy most of its gas from Russia. Authorities in the United Kingdom are cautious—they forced Cuadrilla to suspend its shale drilling after those two small earthquakes in May.
Poland, though, recently threw open its doors to fracking exploration by American firms. Poland burns more coal than almost any EU member, so natural gas would be a welcome alternative. Plus, Poland may have the largest shale-gas reserves in central Europe. “We’ll never be an oil state,” Andrzej Kozlowski, an executive at the Polish oil company PKN Orlen, told The Economist, “but we could become a Norway.”
Poland only has a few fracking wells so far, but it has suffered its own curious flurry of earthquakes over the last few years. They’ve been concentrated around Silesia, a southwestern coal- and metals-mining region. In late 2010 one of the largest quakes, measuring 4.5, killed three men in a copper mine.
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