This isn't just the stuff of comic-book villains: Real humans in the real world—actually, in Oklahoma, of all places—can cause earthquakes.
Scientists have known about man-made earthquakes for decades. They've blame some reservoirs for seismic activity because reservoir water that trickles underground ends up lubricating faults that then slip—or, quake—as a result.
These days, there appears to be a more common and growing culprit: fracking. (Scientists believe it's the deep disposal of wastewater from fracking that incites seismic events.) Some states where fracking is on the rise are in turn experiencing more and more earthquakes—which is why earthquake scientists believe the big one could strike Oklahoma any moment. "People are starting to compare Oklahoma to California in terms of the rate of magnitude-threes and larger," said Robert Williams, a geophysicist for the U.S. Geological Survey.
Earlier this summer, the U.S. Geological Survey issued a warning saying it's crucial for Oklahomans to prepare for the "increased hazard." That prediction is based on a flurry of earthquakes that registered at least 3.0 or higher in magnitude, an uptick that scientists agree is linked to fracking in the state.