The U.S. Geological Survey routinely reports on seismic activity worldwide, and its summary for May 25 lists 33 “events”–one of which turns out to be North Korea’s second nuclear explosion. But government agencies that focus on such signals typically do not rush to report their detailed analysis to the general public. So I and other experts have tried to fill an information vacuum by working intensively in recent days. In a posting on my institution’s website, my colleague Won-Young Kim and I conclude that:
- This was an explosion and not an earthquake;
- It was roughly five times bigger than North Korea’s first nuclear test (on Oct. 9, 2006);
- Because it was so large (the equivalent of thousands of tons of TNT, or several kilotons), it is not credible for it to have been a chemical explosion. It must have been nuclear;
- The seismic stations that monitor that part of the world are of such high quality, that explosions can be detected and identified even down to a few percent of a kiloton.
This all goes to show that expanded seismic networks have made it possible to quickly detect and assess even small nuclear tests.