Bill Menke's BLOG Page: A Bomb Is A bomb Is A Bomb
I've examined the seismograms from the recent (October 9, 2006) North Korean test. It certainly looks like an explosion, since it has amost none of the shear waves that are to be expected from an earthquake. And the strong Rg surface waves indicate that it was shallow, at a depth well within the reach of human industry. Its size is small, around magnitude 4, which corresponds to an explosive yield of about one kiloton, or maybe a little less.
The small size is rather a suprise. For comparison, the US's first atomic test, Trinity, in 1945, was about 19 kilotons, Russia's (in 1949) was 22, France's (in 1960) about 60, China's (in 1964) about 21, India's (in 1974) about 15 and Pakistan's (in 1998) about 30. The newspapers have been full of speculation as to the reason. Was it an intentially diminuitive atomic bomb, a large bomb that fizzled or just a huge pile of a conventional explosive such as TNT?
Unfortunately, this is not a question about which a seismologist like me has much to contribute. Except for mining explosions, which can be easily spotted from their use of ripple firing technology, all explosions look the same. While I can speculate on matter, I cannot add any facts that might lead to answers.
To the seismologist, a bomb is a bomb is a bomb.