Just before 10.30 pm on Wednesday 7 September 2011 an earthquake occurred off the southern coast of Hokkaido Island, Japan. This was measured as having a magnitude of 5.3 on the Richter Scale by the United States Geological Survey, and 5.1 on the Richter Scale by the Japan Meteorological Agency. The depth of the quake is uncertain, but certainly less than 10 km - i.e. very shallow. A quake of this scale at this depth would be devastating in most parts of the world, but Japan is well prepared for earthquakes and there were no reports of any damage or casualties.
Map showing the location of the quake (red cross) and the areas where the quake was felt (circles). The colour of the circles indicates the level of shaking felt, as indicated on the key below. Higher numbers indicate more severe shaking.
Japan lies on the border between four tectonic plates, and is extremely tectonically active. However Hokkaido is less earthquake prone than Honshu, as it has no boundaries passing beneath it. The island was struck by a magnitude 8 quake in 2003, and a magnitude 7.8 quake in 1993. The 1993 quake caused a small tsunami, which killed 203 people.
If you felt this quake you can report it to the United States Geological Survey here.
See also Fukushima shaken by large earthquake, The Nagano Earthquake of 30 June 2011, and Earthquakes on Sciency Thoughts YouTube.