The Oklahoma Corporation Commission says its Induced Seismicity Department and the Oklahoma Geological Survey are investigating several earthquakes in the central part of the state.
At least six quakes 3.0 or stronger have struck since Tuesday in an area about 15 miles northeast of Oklahoma City.
The strongest was a 4.2 quake Wednesday night. It knocked out two electric substations, leaving about 1,900 customers without power for about an hour.
No injuries or significant damage were reported.
The injection of wastewater from oil and gas production into disposal wells has been linked to an uptick in earthquakes, but the commission said Thursday no disposal wells are in the area. A known fault is in the vicinity.