Experts: Okla. quakes too powerful to be man-made
The weekend quakes were far stronger than the weak tremors caused by drilling - especially the controversial practice of hydraulic fracturing, known as fracking. The shaking caused by drilling is usually so weak that it can't be felt.
Experts say the Oklahoma quakes released nearly 16,000 times more energy than the strongest attributed to hydraulic fracturing.
Federal, state and academic experts say preliminary readings show that the Oklahoma quakes are natural, following along the lines of a long-known fault.
The drilling question has been raised because of recent small quakes in Oklahoma and neighboring oil and gas states.
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