Tsunami Warning Issued In Japan Following 6.9 Magnitude Quake George Dvorsky Nov 22, 2016, 9:30am A tsunami warning has been issued in Japan's Fukushima Prefecture after a 6.9 magnitude quake struck of Honshu just before 6:00AM local time. The US Geological Survey had a preliminary magnitude of 7.3 but then downgraded it to 6.9.