According to the USGS:
This figure [below] shows the distribution of earthquakes in north-central Arkansas that have occurred since June 2010. Earthquakes on the figure are color-coded, with red circles denoting earthquakes that occurred from June 4th, 2010 to February 14, 2011, and orange circles denoting earthquakes that occurred from February 15, 2011 to March 1, 2011. The space-time pattern shows a systematic shift in seismicity to the southwest starting on February 15, 2011. White triangles show the location of real-time seismic stations in the vicinity of the earthquake swarm that are used by the University of Memphis and USGS in their complimentary monitoring activities.
More in following posts.