Newswise – Secret underground nuclear tests could now be a thing of the past thanks to a major scientific breakthrough in identifying them.

A team of geoscientists and statisticians say they can now say with 99 percent accuracy whether such an explosion occurred. This is an increase of 82 percent and is based on a data set of known tests in the United States, says the new study published in Geophysical Journal International.

Until now, it has been difficult to distinguish between nuclear explosions and other seismic sources such as natural earthquakes or man-made noise above Earth.

“The explosion goes off and all this energy is radiated, which can be measured with seismometers,” said lead author Dr. Mark Hoggard from the Australian National University (ANU).

“So the scientific problem is: How can we tell the difference between this and a naturally occurring earthquake?”

This was a problem seven years ago, when several of the existing methods for identifying underground nuclear explosions failed to prove that North Korea had conducted such a test.

The secret communist state later confirmed that it had successfully tested a weapon with a strength between 100 and 370 kilotons. For comparison, a 100-kiloton bomb is six times more powerful than the one the United States dropped on Hiroshima in 1945.

North Korea is the only known country to have conducted an underground nuclear test in the 21st century. However, satellite images showed last year that Russia, the United States and China have all built new facilities at their nuclear test sites in recent years.

Although there is no indication that the three superpowers plan to resume such experiments, the war in Ukraine has unsettled the global security landscape.

“By using revised mathematics and more advanced statistical treatment, we have managed to improve the classification success rate for a set of 140 known explosions in the United States from 82 percent to 99 percent,” said Dr. Hoggard.

“Nuclear testing in the US has largely been done in Nevada – in the desert – and there is a thorough seismic record of all of those tests, so it’s a really useful data set.

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

Dr. Hoggard said secret underground nuclear tests could still occur in some parts of the world, and the sheer volume of earthquakes made it difficult to investigate each event to determine whether it was suspicious or not.

“Effective methods like ours are all the more important,” he added.

“There’s no new equipment required either – you don’t need to put up satellites or anything like that, we just use standard seismic data.”

Dr. Hoggard described the model as “quite fast,” making it “more or less suitable for real-time monitoring.”

The research was carried out by a team of geoscientists and statisticians working at ANU and the Los Alamos Government Research Laboratory in the US.

They say the new approach “provides a way to quickly assess the likelihood of an event being an explosion.”

The mathematical model was created by analyzing 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.

After the Cuban Missile Crisis and the Partial Nuclear-Test-Ban Treaty in the 1960s, which limited testing of nuclear weapons only underground, international efforts shifted to monitoring significant seismic waves.

The agreement was introduced following years of environmentally damaging experiments on the surface and/or underwater. These polluted many places and in some cases led to catastrophic radioactive fallout.

But the new monitoring required came with its challenges – particularly the question of how to distinguish between nuclear explosions and other seismic sources.

It’s taken more than six decades, but the scientists behind the new research believe their innovative method is now making it easier for groups like the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), whose mission is international monitoring , could greatly facilitate nuclear testing.

Dr. Hoggard said his team’s mathematical model is “another tool in the CTBTO’s arsenal to detect potential underground tests being conducted in secret.”

He added: “A ban on all future tests is unlikely as several major nations remain unwilling to ratify the Comprehensive Nuclear-Test-Ban Treaty.

“Well-supported monitoring programs are therefore critical to ensuring that all governments are held accountable for the environmental and societal impacts of nuclear weapons testing.”

The article “Seismic moment tensor classification using elliptic distribution functions on the hypersphere” was published in Geophysical Journal International.

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