And it's not just the first two 4.0-plus quakes that have occurred only seconds from one other.

A 3.0 and 3.5 recorded at 4:48 a.m. were only 24 seconds apart, with each located about 19 miles northwest of Fairview. The stronger of the two was around 3 miles deep, while the other was around 2.5 miles below ground.

Almost all of the quakes since Wednesday night were in the Alva-Fairview area. Alva is in Woods County, and Fairview is in Major County. The two towns are about a 50-mile drive apart.

A 2.8-magnitude quake occurred at 12:42 a.m. Thursday near Edmond, and a 2.6 quake occurred at 11:59 a.m. Thursday near Perry. The Edmond area had seen four more earthquakes earlier Wednesday.

A swarm of earthquakes in the Edmond area in late December and early January prompted state regulators to direct that the operators of five disposal injection wells within 10 miles of the heart of the new seismicity cut their injection volumes.

Matt Skinner, Oklahoma Corporation Commission spokesman, said Thursday that he could not provide an exact number of injection wells in the area of the most recent earthquake swarm, but he said "that is a region that has seen a sharp increase in disposed water over the past couple of years."