The 4.0 magnitude earthquake that struck Youngstown on Saturday occurred at an almost identical location to one a week before, a seismologist who studied the quakes said Monday. Both earthquakes occurred close to the bottom of a 9,200-foot-deep disposal well where for months, brine and other liquid waste from natural-gas wells had been injected under pressure. They were the 10th and 11th earthquakes to occur near the well since March, but the first to be precisely located.

The finding provides further evidence to support what some scientists had suspected: that the waste, from the drilling process called hydraulic fracturing that is used to unlock natural gas from shale rock, might have migrated from the disposal well into deeper rock formations, allowing an ancient fault to slip.

Read more: Ohio – Sites of Two Earthquakes Nearly Identical – NYTimes.com.