Noticing Nukes

In the wake of North Korea’s nuclear weapons test on Tuesday, Forrest Wickman wonders if it is possible to conduct such a test on the sly:

[T]he best bet would be to hollow out a large, round cavern deep underground and blow up a small device at the center of it. Because such a bomb would have a less immediate impact on the rock around it… its seismic impact could be of a small enough magnitude to go undetected. However, because of the difficulty of building such a large hole without drawing attention, it’s unlikely that any country would be able to hide an explosion of more than 1 or 2 kilotons. For comparison, the bombs dropped on Hiroshima and Nagasaki yielded explosions of 15 and 22 kilotons, respectively.