A 6.4-magnitude undersea earthquake on Monday jolted the sea area off the east coast of Honshu, the main island of Japan, US seismologists said, but no tsunami alert was issued.
The US Geological Survey said the quake had a depth of 31 kilometres and hit at 4:32 am (2:02 IST) some 140 kilometres east of the city of Sendai.
In March last year a 9.0-magnitude undersea earthquake off Japan's northeast coast triggered a monster tsunami, leaving about 19,000 people dead or missing and crippling the Fukushima nuclear power plant.