An earthquake has shaken part of northwestern Oklahoma. The US Geological Survey says the 3.1 magnitude earthquake was recorded at 6:50 am Saturday more than 10 miles (16 kilometers) northeast of Helena in Alfalfa County. The earthquake was recorded at a depth of about 3 miles (5 kilometers). No damage or injuries were immediately reported. Geologists say damage is not likely in earthquakes below magnitude 4.0. Earthquakes of magnitudes 2.5 to 3.0 are generally the smallest that are felt by humans.
Thousands of earthquakes have been recorded in Oklahoma in recent years. Many have been linked to the underground injection of wastewater from oil and natural gas production operations. State regulators have directed oil and gas producers to close some disposal wells or reduce the volume of fluids they inject in others.