States where hydraulic fracturing is taking place have seen a surge in earthquake activity, raising suspicions that the unconventional drilling method could be to blame, especially the wells where the industry disposes of its wastewater.
Fracking generates vast amounts of wastewater, far more than traditional drilling methods. The water is pumped into injection wells, which send the waste thousands of feet underground. No one knows for certain exactly what happens to the liquids after that. Scientists wonder whether they could trigger quakes by increasing underground pressures and lubricating faults.
Oklahoma has recorded nearly 250 small-to-medium earthquakes since January, according to statistics kept by the U.S. Geological Survey. That's close to half of all the magnitude 3 or higher earthquakes recorded this year in the continental United States.
A study published earlier this month in the journal Science suggests that just four wells injecting massive amounts of drilling wastewater into the ground are probably shaking up much of the state, accounting for one out of every five quakes from the eastern border of Colorado to the Atlantic coast.