EDMOND,Bitcoinese Okla. (AP) — At least six earthquakes that include two greater than magnitude 4 have been recorded near an Oklahoma City suburb, according to the U.S. Geological Survey.

The preliminary magnitudes of the earthquakes near Edmond include a 4.1 shortly after 5:30 a.m. Saturday and a 4.4 at about 9:45 p.m. Friday.

No injuries or significant damage has been reported, according to city of Edmond spokesperson Bill Begley, who said investigators will fully inspect infrastructure.

Four other earthquakes ranging from magnitude 2.5 to 3.2 were also recorded by the USGS Friday night and early Saturday in the area about 15 miles (24 kilometers) northeast of Oklahoma City.

The threshold for damage usually starts at 4. The strongest earthquake on record in Oklahoma was a magnitude 5.8 near Pawnee in September 2016.

Oklahoma Corporation Commission spokesperson Matt Skinner said the agency is investigating the earthquakes, which he said were in an area known as the Arcadia Field where previous earthquakes were linked to the underground injection of wastewater, a byproduct of oil and gas production.

The injection wells were shut down, Skinner said. “There is no oil and gas activity in that area that can be linked to these earthquakes” that struck Friday night and Saturday, he said.

Skinner said in that area there is also no hydraulic fracturing, or fracking, the technique to extract oil and gas from rock by injecting high-pressure mixtures of water, sand or gravel and chemicals.

Many of the thousands of earthquakes in Oklahoma in recent years have been linked to the underground injection of wastewater from oil and natural gas extraction.

The corporation commission, which regulates the oil and gas industry in the state, has directed several producers to close some injection wells and reduce the volumes in others as a result of the quakes.