By VOA

Since 2009, earthquake activity has greatly increased in the central and eastern United States. A new report from U.S. earthquake experts links drilling for oil and gas with the rise in the number of earthquakes in those areas.

It is widely known that certain parts of oil and gas drilling can lead to small earthquakes. The United States has expanded its oil and gas production in recent years.

Critics blame the use of a drilling method known as hydraulic fracturing, or fracking, for the increase in earthquakes. Fracking involves forcing high-pressure water, sand and chemicals into rock formations deep underground.

Chad Devereaux works at cleaning up the bricks that fell from three sides of his in-laws home in Sparks, Oklahoma, Nov. 6, 2011, after two earthquakes hit the area in less than 24 hours.

The U.S. Geological Survey published a report on a study of 17 fracking areas within eight states in the central and eastern parts of the U.S. Those states include Alabama, Arkansas, Colorado, Kansas, New Mexico, Ohio, Oklahoma and Texas. Fracturing the underground rock releases oil and gas trapped inside. It also creates a large amount of wastewater. Roger Musson of the British Geological Survey says the problem is what to do with that water. Mr. Musson spoke to VOA by telephone.

He says injecting wastewater into the ground to dispose of it is what causes earthquakes in the affected areas.It does this by loosening faults, or divisions, in the rocks that make up Earth's crust.

"Below the water table, there is water in the rocks. And if you change the pressure in that water, then it has the effect of lubricating the faults," he says.The USGS report says the new areas of earthquake activity are located "near deep fluid injection wells or other industrial activities capable of inducing earthquakes."The most significant increase has occurred in the central U.S. state of Oklahoma. Before 2008, Oklahoma had just one or two earthquakes a year with a magnitude of 3.0 or greater. Now, Oklahoma has one or two such earthquakes every day.In a recent report, the state of Oklahoma said for the first time it is "very likely" that the rise in earthquakes has been caused by the disposal of wastewater from oil and gas drilling.Most of the so-called manmade earthquakes have been small and have done little damage. But experts warn there is no guarantee earthquake activity will not increase and cause more damage."This is being debated very urgently by seismologists," Roger Musson says. Currently, scientists believe that wastewater injection can produce earthquakes in the magnitude 4 or 5 range. "But the upper limit is really very difficult to judge," Mr. Musson says.Environmental rights activists have criticized fracking. They say it pollutes groundwater and sends harmful gases into the atmosphere.

Supporters of fracking say the innovative drilling process has helped grow the U.S. economy and has reduced American dependence on foreign oil. They add that the reports linking earthquakes to drilling activity are exaggerated.

William Gallo reported this story from Washington. Jonathan Evans adapted it for Learning English. Ashley Thompson was the editor.

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Words in This Story

fracture – v. to cause a crack or break in something hard

fault – n. a break in the Earth's crust

inject – v. to force a liquid into something

innovative – adj. introducing or using new ideas or methods

magnitude – n. a number that shows the power of an earthquake

exaggerate – v. to describe something as larger or greater than it really is