At least five earthquakes have shaken Oklahoma this morning. The latest had a magnitude of 4.2, while the previous four ranged in strength from 2.8 to 4.3, NewsOK reports. No damage has been reported thus far, the site notes. Much of the state's central region felt the rumblings. "At this point it looks like a main shock, aftershock sequence. There are even a bunch of smaller ones," says an expert. The state's strongest-ever earthquake hit a magnitude of 5.7, he adds. (More Oklahoma stories.)