Oklahoma has been a little shaky lately. On Aug. 19, the Sooner State was rattled by 20 earthquakes in one day, according to data from Oklahoma’s Geology Survey. It’s the latest manifestation of a significant increase in seismic activity in Oklahoma, which scientists believe is being caused by hydraulic fracturing, AKA fracking, to tap into oil and gas under the surface, and by the injection of wastewater from oil-gas wells into brine reservoirs underground.

While most of the quakes were so small — below a magnitude of 3 — that Oklahoma residents may barely have noticed them, the 10,000 inhabitants of Guthrie, Okla. definitely felt the 4.3 quake that rattled their small city at 7:45 a.m. The vibrations caused a local newscaster to raise her hands in the midst of a segment and shout, “earthquake!”

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A local liquor store owner captured the quake’s effects on this security camera video. “This one was a big boom a bang,” explained store owner Mark Uselton. At one end of the store, wine bottles rattled and teetered on the edge of the shelf, and stacked cases of beer swayed with the vibration. Amazingly, when the ground stopped shaking, Uselton found that only three of the 7,000 bottles in his store had broken. Even so, the quake was–to excuse the pun–an unsettling experience that “could have done some serious damage,” the store owner said.

That quake, though, may have just been a warning shot. At the Seismological Society of America annual meeting in Anchorage, Ak., in May, a panel of scientists warned that underground disposal fracking wastewater may pose a much greater risk of causing dangerous earthquakes than previously believed, particularly in areas here earthquake faults haven’t been thoroughly mapped.

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Even more alarmingly, the scientists said they can’t yet predict which wastewater-injection sites are likely to pose threats to buildings or critical infrastructure such as power plants, and they’re not sure how drilling operators can mitigate the hazard. Also, research suggests that disposal wells can affect earthquake faults that are miles away.

In 2011, Oklahoma experienced a 5.7 quake that scientists concluded most likely was caused by fracking.