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Study: Far quakes can ripple to oil, gas fields

LOS ANGELES -- The earthquake that rocked Japan in 2011 set off tremors around a West Texas oil field, according to new research that suggests oil and gas drilling operations may make fault zones sensitive to shock waves from distant quakes.

It's long been known that large quakes can trigger minor jolts thousands of miles from the epicenter. Volcanically active spots such as Yellowstone National Park often experience shaking after a distant event.

Less is known about the influence of remote quakes on fault lines that have been weakened by man-made activity such as the deep disposal of wastewater at the Texas oil field. A new study led by researchers at Columbia University and published today in the journal Science suggests that a strong quake halfway around the globe can set off small to mid-size quakes near injection wells in the U.S. heartland.

"The seismic waves act as the straw that breaks the camel's back, pushing the faults that last little bit toward an earthquake," lead researcher Nicholas van der Elst said.

Research has shown that wastewater disposal, the process of pumping fluids deep into the ground at high pressures, can weaken nearby fault lines and even produce quakes big enough to be felt.

The controversial practice of hydraulic fracturing, or fracking, which uses high-pressure mixtures of water, sand and chemicals to extract natural gas or oil, also can trigger quakes, but they're typically microquakes -- smaller than magnitude 2.

By poring through the quake archives, van der Elst and colleagues found evidence that faults near wastewater injection sites were loaded with stress when ripples from a faraway earthquake traveled around the planet.

They contend that the magnitude 9 Japan quake set off a swarm in the West Texas town of Snyder, where oil extraction has caused shaking in the past and the magnitude 8.8 Chile quake in 2010 triggered a magnitude 4.1 in Prague, Okla., home of active injection wells.

In those instances, the triggered seismic activity was followed months later by a moderate quake and researchers say that could be a warning sign of stress on the fault. Not all sites near injection wells showed increased shaking after a strong distant quake. The team found the most affected areas were places where pumping has been going on for decades.

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