An earthquake measuring 5.1 on the Richter scale jolted 112km N of Yonakuni, Japan at 02:49:40 Hong Kong Time on Tuesday (18:49:40 Monday GMT), the U.S. Geological Survey said. The epicenter, with a depth of 228.6 km, was initially determined to be at 25.4726 degrees north latitude and 122.8348 degrees east longtitude.