Seismographs at the College of Charleston did not report any earthquakes, said Erin Beutel, S.C. Earthquake Education and Preparedness director. She suspected sonic booms, but a public affairs officer for the Marine Corps Air Station in Beaufort said no F-18s were flying in the area at that time. A public affairs officer for the Charleston Air Force Base said C-17s were operating, but not fast enough to cause sonic booms.
http://www.postandcourier.com/news/2011/mar/15/booms-revive-an-old-mystery/