UPDATE: THE UNITED STATES GEOLOGICAL SURVEY ANNOUNCED JUST AN HOUR AGO THAT THE EARTHQUAKE THAT RATTLED MOST OF OKLAHOMA AND WAS FELT AS FAR AWAY AS KANSAS AND TEXAS WAS A 4.7 MAGNITUDE. This morning about 9:15, I was busy packing when I heard a plane overhead.  Since we're only a couple miles from the airport, it's not unusual for planes to come over the house low and fast. 
What is unusual is for these planes to create sonic booms because they are passenger jets, not fighter jets.  Nonetheless, suddenly I heard a loud sound just like a sonic boom.  Simultaneously, the windows rattled and the house shook.  
"Wow!" I thought.  "That was one heck of a sonic boom!"
Turns out, it was NOT a sonic boom.  It was an earthquake.  The loud boom was the sound of the tectonic plate being lifted up and slammed back down.  The national center for earthquakes quantified it as a 4.1 while the Oklahoma Geological Center(OGC) stated it was a 5.1. Amazingly, the OGC reported that there have been 78 earthquakes in Oklahoma in the last 30 days.  Most were so minor that people barely felt them, if at all.
There is a fault line that runs vertically through Oklahoma from the Kansas border to the Texas line.  For the last couple of years , it has been active with several minor quakes along it.
This is the first  that has hit near Oklahoma City with the epicenter of today's shaking centered just east and south of Norman.  So far the only measurable damage is a few broken windows, although officials are taking close looks at elevated bridges and OU's football stadium, which will be filled with 85,000 people Saturday.  People in Norman reported being slammed against walls with the sound reminding them of a freight train or a tornado.
Amazingly, reports came in from as far away as Kansas City and Dallas from people who felt the quake, so this was much more significant than anything that has hit Oklahoma in over 100 years.
Experts said to expect some aftershocks, although we have not had one yet.