Kyodo News reporting that a 6.3 aftershock has hit Chiba Prefecture.  Narita airport has been shut down to check for cracks in the runways.

The epicenter is off the coast of Chiba Prefecture, which is just east of Tokyo, basically the east central coast of Japan, south of where the March 11 quake happened.

Less than an hour prior, Nagano Prefecture got hit with a 5.5 quake.