The earthquake - at a depth of 49km (32 miles) - struck close to the epicenter of the 11 March quake, which triggered a devastating tsunami.
Japanese authorities ordered a new evacuation from the warning zone.

The workers are trying to keep the damaged reactors cool to stop further releases of radioactive material.
Thursday's quake struck at 2332 local time (1432 GMT) on Thursday, 118km (78 miles) north of Fukushima, 40km offshore.
First reports said it had a magnitude of 7.4 but that was later revised downwards to 7.1, according to the US Geological Survey (USGS).
Last month's earthquake had a magnitude of 9.0 and struck at 32km deep.