What happens in Oklahoma doesn’t stay in Oklahoma, at least not when it comes to earthquakes.

That was evident Saturday morning when a 5.6 magnitude earthquake centered in Pawnee, Okla., shook residents awake in Lawrence some 250 miles to the northeast. The earthquake was the biggest in Oklahoma since 2011 when a 5.6 magnitude quake struck Prague in the center of the state. Saturday’s earthquake was felt from Dallas to Des Moines and from St. Louis to Fayetteville, Ark. Fortunately no serious injuries were reported in connection with the quake and damage was limited.

Still, Saturday was an alarming reminder of the increasingly dangerous connection between wastewater produced by oil and gas drilling and earthquakes. No one can say for sure that Saturday’s quake was caused by drilling, but note that the first step Oklahoma officials took in response to the earthquake was to order 37 of the state’s 4,000 underground disposal wells to be shut down.

It is these disposal wells that are at the center of the quake controversy. Disposal wells are used to get rid of wastewater — a mixture of saltwater, oil and chemicals — that results from drilling. The wastewater is injected into wells deep underground, oftentimes even deeper than the pockets of oil and gas. The Associated Press reports that in Kansas one barrel of oil produces 16 barrels of wastewater polluted with oil and salt.

It is the disposal of wastewater underground that geologists say is responsible for the spike in earthquakes in southern Kansas and northern Oklahoma, a region that now rivals Northern California as the country’s most earthquake prone.

After going from no earthquakes in 2012 to more than 120 in 2014, Kansas responded by placing limits on the volume of wastewater that is injected in the most earthquake-prone areas of Kansas. Those caps have produced a measurable decrease in seismic activity and the Kansas Corporation Commission recently expanded the caps to other quake-prone areas. Pennsylvania has severely limited the number of wells and most of the state’s wastewater is shipped to Ohio for disposal. Officials in Texas are increasingly mandating the recycling of wastewater as a means of dealing with drought.

By contrast, Oklahoma has been slower to respond, only starting to shut down wells earlier this year.

Variations in state guidelines in wastewater well injections are a risky proposition, especially for neighboring states. Unlike state regulations, earthquakes know no boundaries as Saturday’s event demonstrated all too well.