Water left over from oil and natural gas production may strengthen the magnitude of earthquakes in states like Oklahoma and Kansas, according to a new study.

Dense, salty water pumped deep into the Earth is putting stress on small, hidden fault lines scattered throughout oil-producing regions.

“It doesn’t take a large fault to generate a damaging earthquake,” says Martin Chapman, a seismologist at Virginia Tech.

He described the small fault lines found across the country as ubiquitous. “The whole crust is fractured by these kinds of faults,” he says.

And while scientists have long known that wastewater can trigger earthquakes, the new study published in the journal Nature finds that the water may be sinking deeper than previously thought, leading to