The US Geological Survey has recorded seven small earthquakes shaking central Oklahoma in a span of just about 14 hours.
They ranged from magnitude 2.6 to 2.9 and were centered in the Guthrie, Jones and Langston areas, 15 miles to 30 miles (24 to 48 kilometres) northeast of Oklahoma City.
The USGS said the quakes were recorded between 7:57 pm Saturday and 9:51 am Sunday, local time. No injuries or damage were reported.
Those follow four other quakes, including a 4.3-magnitude temblor near Langston recorded shortly after noon Saturday. The other Saturday morning quakes ranged in magnitude from 2.9 to 3.2.
Residents in central Oklahoma have said they want to know whether the surge in earthquake activity in the region is caused by oil and gas drilling operations in the area.
At a meeting with regulators and research geologists last month in Edmond, many urged regulators to ban or severely restrict the wells that are used to dispose of wastewater from drilling and that some scientists say could be linked to the quakes. Officials, meanwhile, are trying to reconcile the scientific data with the interests of their citizens and the oil and gas industry.
Austin Holland, a research seismologist with the Oklahoma Geological Survey, said at the time that the state is experiencing unprecedented earthquake activity and his agency is closely monitoring it to determine whether the earthquakes are a natural phenomenon or are man-made.
Holland said the same drilling methods have been used in the state for years but that frequent earthquakes did not become a problem until after 2009.
