Underground nuclear tests now 99% detectable, scientists say

Secret underground nuclear tests could soon be a thing of the past, thanks to a major scientific breakthrough in how to identify them.

It has previously been tricky to differentiate between nuclear explosions and other seismic sources, such as naturally occurring earthquakes or man-made noise above ground. This was certainly an issue seven years ago, when several of the existing methods used to identify underground nuclear explosions failed to establish that North Korea had carried out such a test. The secretive communist state later confirmed it had tested a weapon with a force of 100–370 kilotons, several times more powerful than the one the US dropped on Hiroshima in 1945.

There may still be instances of underground nuclear tests being carried out surreptitiously in some parts of the world, and the sheer volume of earthquakes makes it difficult to investigate each event to determine if it is suspicious or not. As noted by Dr Mark Hoggard of The Australian National University (ANU), “The explosion goes off and you have all this energy that radiates out, which can be measured on seismometers.

“So, the science problem becomes, how do we tell the difference between that and a naturally occurring earthquake?”

This issue now appears to have been resolved, thanks to research on a dataset of known nuclear tests carried out by Earth scientists and statisticians working at ANU and the Los Alamos government research lab in the US. They say their new approach, described in Geophysical Journal International, provides a means to rapidly assess the likelihood of an event being an explosion.

The mathematical model was built by analysing the physical differences in the pattern of rock deformation at the source of nuclear explosions and earthquakes, allowing experts to determine which seismic event a recorded noise is more likely to belong to. As explained by Hoggard, “Nuclear testing in the US has largely been carried out in Nevada — in the desert — and there is a thorough seismic record of all those tests, so it provides a really helpful dataset.

“By using some revised mathematics and more advanced statistical treatment, we have managed to improve the classification success rate from 82% to 99% for a series of 140 known explosions in the US.

“Our new method also successfully identifies all six of the tests conducted in North Korea from 2006 to 2017.”

Hoggard said the new model is “pretty fast”, making it suitable for real-time monitoring. “It also doesn’t require any new kit — you don’t have to put up satellites or anything like that, we’re just using standard seismic data,” he said.

The scientists behind the new research believe their innovative method could make things a lot easier for groups such as the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which is tasked with international surveillance of nuclear testing. Hoggard described the new mathematical model as “another tool in CTBTO’s armoury for detecting any potential underground tests that are conducted in secret”.

“A ban on all future tests is unlikely, given that several major nations remain unwilling to ratify the Comprehensive Nuclear-Test-Ban Treaty,” he said.

“This makes effective methods like ours all the more important.”

Image credit: iStock.com/Dennis Swanson - Studio 101 West Photography