The Guardian reports that Russian defense experts estimated the North Korean explosion's yield at between 10 and 20 kilotons, many times more than the 1 kiloton measured in its first nuclear test in 2006, and about as powerful as the bombs the US used against Hiroshima and Nagasaki at the end of the second world war. (One kiloton is equal to the force produced by 1,000 tons of TNT.)
The force of the blast made the ground tremble in the Chinese border city of Yanji, 130 miles away.
Koh Yu-hwan, a professor at Dongkuk University in Seoul, told Reuters, "North Korea had been expecting the new US administration to mark a shift from the previous administration's stance, but is realizing that there are no changes. It may have decided that a second test was necessary.”
Analysts believe the North Korean leader, Kim Jong-il, hopes to use the test to shore up support from the military amid mounting speculation that he is about to name one of his three sons as his successor.