Magnitude 6.1 earthquake strikes northern Japan

A preliminary magnitude 6.1 earthquake struck northern Japan early Monday, the United States Geological Survey reported, with no immediate reports of casualties or damage.

The quake hit about 18 kilometers west of Sarabetsu in Hokkaido at a depth of 81 kilometers, according to the agency.

Last week, a stronger magnitude 7.7 earthquake off northern Japan triggered a brief tsunami alert and raised concerns over a potential megaquake risk along coastal areas.