|A record 262 aftershocks of magnitude 5 or greater were registered in the seven days following the magnitude 9.0 earthquake off northeastern Japan on March 11, Kyodo News quoted the Japan Meteorological Agency as saying Friday.
Meanwhile, there were three aftershocks of magnitude 7 or greater, including one magnitude 7.5 that occurred shortly afterwards, and 49 aftershocks of magnitude 6 or more, according to Kyodo.
The aftershocks have occurred in waters off a wide stretch of land from Iwate to Ibaraki prefectures in a zone 500 kilometers in length and about 200 km in width, the agency said.
The National Police Agency said Friday that the catastrophic March 11 earthquake and ensuing tsunami have left 6,911 people dead and 10,316 others unaccounted for by 7:00 p.m.(1000 GMT).
The quake also caused nuclear crisis at the Fukushima Daiichi nuclear power plant. On Friday, Japan raised the severity level of quake-hit reactors at the Daiichi nuclear power plant from 4 to 5 on an international scale of 7. Efforts are continuing to cool down the overheating reactors and spent fuel a week after the massive earthquake and tsunami as International Atomic Energy Agency chief Yukiya Amano made an emergency visit to Tokyo.