Powerful 7.4-magnitude earthquake strikes off Japan and tsunami alert issued

A powerful earthquake has struck off the northern Japanese coast and the Japan Meteorological Agency has issued a tsunami alert in the region, warning of an increased risk of a possible mega-quake.The Cabinet Office and the Japan Meteorological Agency said there is 1% chance of a mega-quake occurring on the northern Japanese coast in the next week or so, following the powerful quake earlier near the Chishima trough.