[LETTERS TO THE EDITOR]Maybe underground tests?

I had questions on “Mystery explosions rock North Korea”(Sept. 13). “Immediately after the blasts, a concussion of 2.6 on the Richter scale was detected,” the official said. “Some are talking about a possible nuclear test, but our image data show that there was no mushroom-shaped cloud, a sign of a nuclear test.”

Is this also eliminating the possibility of underground testing? Mushroom clouds usually form in atmospheric tests; underground testing can produce ejection of nuclear dust if the crater leaks during the explosion.

by Mathieu Benoit