A 5.5-magnitude earthquake struck off the east coast of Japan on Monday, the US Geological Survey reported, but no tsunami warning was issued.
The quake hit at a depth of 26 kilometres (16 miles) at 3:13 am (1813 GMT Sunday), about 324 kilometres east of the town of Namie, the USGS said.
The Pacific Tsunami Warning Center did not issue an alert.
A powerful 7.1-magnitude undersea quake off the east coast two days ago triggered a small tsunami, which was recorded as being as high as 55 centimetres (22 inches) in one place.
Workers were evacuated from the crippled Fukushima nuclear plant on Saturday but there were no reports of any damage. Japan's meteorological agency said the quake was an aftershock of the disastrous March 2011 tremor.
The quake-tsunami disaster two years ago left more than 18,000 people dead and battered the Fukushima plant in the world's worst atomic disaster in 25 years.