Japanese officials issued tsunami warnings and evacuated a crippled nuclear plant after a strong earthquake struck the nation’s northeast coast Monday.

The U.S. Geological Survey initially reported the magnitude of the quake at 7.1, the same strength as a major aftershock that hit on Thursday, but later revised it downward to 6.6. A tsunami warning was issued for portions of the northeast coast – the same area hit by a massive earthquake and tsunami on March 11 – but was lifted after less than one hour.