This is very abnormal for Oklahoma. The 4.7 quake Saturday morning was the 2nd strongest ever recorded in Oklahoma. The strongest was (emphasis on “was”) a 5.5 in 1952. This 5.6 is one for the records, I hope. Further up the scale would mean increasing amounts of damage. Let’s hope this 5.6 is the strongest ever in Oklahoma for a long time to come.
From a geologist's perspective it's pretty routine, actually. Had an earthquake nearby of almost the same magnitude in 1952, which in term of geology is seconds ago.
And central Oklahoma has clear seismic hazard shown on USGS seismic hazard maps.
http://boingboing.net/2010/10/14/earthquakes-in-oklah.html
http://www.okgeosurvey1.gov/pages/earthquakes/information.php