Oil-drilling wastewater pumped into a northeast Ohio well “almost certainly” triggered 11 minor earthquakes around Youngstown since last spring, including one Saturday, a seismologist tells the Associated Press.

Ohio officials closed four inactive “fluid injection” wells within a five-mile radius of the Youngstown well, which is near a fault that geologists apparently weren’t aware of. Pressure from the wastewater caused the fault to shift.Northstar Disposal Services has used the wells to dispose of brine wastewater from shale oil and gas drilling, which officials said is different from so-called fracking, the Youngstown Business Journal and AP report.