A 7.7 magnitude earthquake Monday off northern Japan sparked a short-lived tsunami alert and an advisory of a slightly higher risk of a possible megaquake. The Cabinet Office and the Japan Meteorological Agency said there was a 1% chance for a megaquake, compared to a 0.1% chance during normal times, in the next week or so following the quake near the Chishima and Japan trenches. Officials said the advisory was not a prediction but urged residents in northeastern coastal towns to raise their preparedness. Two people were injured and a small tsunami was measured in two ports.