The tremor was recorded on the night of February 13-14, 55 kilometers from Fukushima Prefecture.
There were no tsunami warnings.
At least 950,000 homes were left without electricity.
A government source said the power outage situation is expected to improve in the early hours of Sunday.
A spokesman for the Meteorological Agency said aftershocks of up to 6 on the Japanese scale could be observed for at least a week. The official said the earthquake on Saturday was believed to be the aftermath of a large earthquake that struck eastern Japan on March 11, 2011.

“Since the 2011 earthquake was very strong, with a magnitude of 9.0, it is not surprising that an aftershock of this magnitude occurred 10 years later,” said Kenji Satake, a professor at the Earthquake Research Institute at the University of Tokyo.
According to Tokyo Electric Power, no abnormalities have been found at Fukushima NPPs 1 and 2.
On February 11, a devastating tornado swept along the coast of Turkish Izmir. Beginning with heavy rain, the hurricane caused significant damage and caused flooding of boats and road accidents.

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