Data from a seismic station in Mudanjiang, China, also was used by Kim and his colleagues last week to study North Korean tests in 2009 and 2006. There is also genuine earthquake data from that station, as well as artificial explosions of non-nuclear sorts, used to generate seismic waves to study the structure of a volcano in the same area, said Kim. All that comparative data has made it possible to glean quite a lot from the new signal, he explained.
This week's test shows that the North Koreans are definitely learning the practical details of how to put material together, press the button, and get more out of it each time, he said.
"They are very similar signals (in 2009 and 2013), so it must be the same tunnel in the mountain." said Kim.
In fact, it looks like the latest bomb was detonated as little as 200 meters from the previous test, he said.
As for why non-government scientists are studying the test at all, when there are government scientists using more numerous and classified seismic stations in the area, it's a matter of wanting to shine a light.