The Japan Meteorological Agency says the strong earthquake that struck Tuesday off the coast of Fukushima prefecture was an aftershock of the magnitude 9.0 earthquake that spawned a deadly tsunami in the same region in 2011.
The agency warned that another large quake could hit in the next few days and urged residents to remain cautious for about a week.
Today's magnitude 7.4 quake triggered moderate tsunamis, but nothing high enough to cause major damage.
It was the largest earthquake in the northeast Japan region since the 2011 quake and some large aftershocks the same day.
All tsunami warnings and advisories have been lifted in Japan, seven hours after the quake.