6.1 earthquake hits off Japan's coast: USG A 6.1-MAGNITUDE earthquake has struck off the south coast of Japan's main Honshu island, but no tsunami warning was issued. The quake hit 644km south of Tokyo, at a depth of 424km, the United States Geological Survey said. Another, weaker 4.2-magnitude quake struck in Fukushima prefecture in the northeast at a shallow depth of 10km and was felt throughout the region, the Japan Meteorological Agency said. It had no impact on the tsunami-ravaged Fukushima Daiichi plant, its operator Tokyo Electric Power Company said.