More than 500 measurable earthquakes have occurred in central Arkansas since September, and it's unknown if they'll stop anytime soon, seismologists say.

Researchers with the U.S. Geological Survey say they ranged in magnitude from a barely noticeable 1.8 to a very noticeable 4.0 temblor recorded Oct. 11, CNN reported Friday.

Locals say they are looking forward to the quakes going away.

"In the beginning, it was fun, it was neat, it was a cool thing to experience," Steve Wilson, assistant superintendent at Woolly Hallow State Park, said. "We've had all the fun we want."

Drilling for natural gas has been ruled out as a cause for the quakes, but experts are looking at saltwater disposal wells, Scott Ausbrooks, geohazards supervisor for the USGS, said.

Disposal wells are created when drilling waste is injected back into the earth after drilling.

The Arkansas Oil and Gas Commission issued an emergency moratorium on permits for new disposal wells earlier this month.

"I think everyone recognizes that there is an increased number of seismic events occurring in and around this area," Shane Khoury, deputy director and general counsel for the Arkansas Oil and Gas Commission, said. "If you look at the maps, at least circumstantially, there appears to be evidence that they may be related to disposal operations."

"But we also know that this is an area that is historically active," he said.