A magnitude 4.5 earthquake hit near Edmond, Oklahoma (just north of Oklahoma City) at 12:10 p.m. local time on 7 December 2013. The "did you feel it" map is from the USGS:
In addition, on 8 December 2013 there were several aftershocks, including a magnitude 3.1 quake just after midnight local time.
Reuters has a good overview of the Oklahoma earthquake situation in a November 11, 2013 article by Carey Gillam. Quakes are up sharply in recent years, and the ongoing concern is that they are related to the fracking (hydraulic fracturing) techniques used in the oil and gas industry. From Reuters: "In Oklahoma, water, fracking - and a swarm of quakes"
Seismologist Austin Holland wants to start an earthquake.
From his office a few feet below the earth's surface - a basement at the University of Oklahoma in Norman - Holland, who tracks quakes for the Oklahoma Geological Survey, is digging into a complex riddle: Is a dramatic rise in the size and number of quakes in his state related to oil and gas production activity? And, if so, what can be done to stop it?
As part of his wide-ranging research, Holland is proposing to inject pressurized water into porous rock in an area already known to be earthquake-prone, to see whether injections of oil industry wastewater are contributing to a "swarm" of earthquakes rocking the state.