A series of strong offshore earthquakes measuring above 6.0 on the Richter scale shook Japan early on Thursday. Seismologists said, there was however no danger of a destructive tsunami. The latest was a 6.8-magnitude quake that hit at 6:24 am local time, 400 kilometres northeast of Tokyo at a shallow depth of nine kilometres below the Pacific seafloor. The tremors follow a major 7.3 quake on Wednesday which swayed buildings in Tokyo and triggered a small tsunami but did not cause any casualties or property damage.