A spate of relatively small earthquakes that rattled northeast Ohio last year were quickly tried to hydraulic fracturing, prompting the state to announce new restrictions and rules for the practice.

This week, a new study says that there were actually dozens of quakes in March 2014, including one with a magnitude of 3.0, and linked them to hydraulic fracturing in the area.

Hydraulic fracturing, better known as fracking, involves blasting water and chemicals into wells to fracture the rock and release natural gas. Geologists in Ohio said after the March 2014 quakes near Youngstown that the injection of sand and water during the fracking process put pressure on a fault there, the Ohio Department of Natural Resources said.

The new study published by the Bulletin of the Seismological Society of America goes further, finding that dozens of additional quakes that were not felt in the area occurred over several days.

“This activity did not create a new fault, rather it activated one that we didn’t know about prior to the seismic activity,” Robert Skoumal, one of the study’s authors, said in a statement released by the society.

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Researchers looked at 77 quakes with magnitudes between about 1.0 and 3.0 that occurred between March 4 and March 12 last year. They studied these quakes and “active hydraulic fracturing operations,” ultimately finding a link between the well activities and the timing and location of the earthquakes, which occurred around Poland Township, which is near Youngstown and not far from the Pennsylvania border.

There were activities at other wells in the area that did not result in any tremors, though. Skoumal said that this means “a relatively small portion” of the fracking activities were responsible for tremors.

Not long after the March 2014 quakes, the Ohio Department of Natural Resources announced stronger permit requirements for drilling activities near faults or areas that have experienced seismic activities. Between 1999 and 2014, Ohio had experienced 109 earthquakes of at least a 2.0 magnitude, the state Department of Natural Resources said.

Earthquake activity has been on the rise in some parts of the country, something experts have linked to fracking activities. In Oklahoma, for example, there has been an incredible surge in the number of quakes recently. By May of last year, the state hadeasily broken its previous record for most earthquakes of at least a 3.0 magnitude in a single year.

The U.S. Geological Survey and Oklahoma Geological Survey said that the rising number of earthquakes there stemmed from wastewater being injected into deep disposal wells. Wastewater is a byproduct of oil and gas production, and millions of gallons of it are created during fracking. A study published in Science last year found that fracking couldn’t be directly tied to the increasing number of earthquakes, but said that the disposal of wastewater was probably behind the surge.

Meanwhile, a series of earthquakes in the Dallas area have prompted worry there and raised the specter of fracking. “Some are blaming fracking, though from what I understand, we don’t currently have any fracking in Irving,” Irving Mayor Beth Van Duyne told the Dallas Morning-News. A seismologist for the state’s Railroad Commission, which regulates oil and gas in Texas, said he believed wastewater disposal wells were not responsible.

It is still unclear what is causing the earthquakes, one of which had a magnitude of 3.6. Southern Methodist University and the U.S. Geological Survey are sending seismic sensors to the region to try to collect data and figure out what is happening.