Underground nuclear tests are hard to detect. A new method can spot them 99% of the time

US Department of Energy via Wikimedia Mark Hoggard, Australian National University

Since the first detonation of an atomic bomb in 1945, more than 2,000 nuclear weapons tests have been conducted by eight countries: the United States, the Soviet Union, the United Kingdom, France, China, India, Pakistan and North Korea.

Groups such as the Comprehensive Nuclear-Test-Ban Treaty Organization are constantly on the lookout for new tests. However, for reasons of safety and secrecy, modern nuclear tests are carried out underground – which makes them difficult to detect. Often, the only indication they have occurred is from the seismic waves they generate.

In a paper published in Geophysical Journal International, my colleagues and I have developed a way to distinguish between underground nuclear tests and natural earthquakes with around 99% accuracy.

Fallout

The invention of nuclear weapons sparked an international arms race, as the Soviet Union, the UK and France developed and tested increasingly larger and more sophisticated devices in an attempt to keep up with the US.

Many early tests caused serious environmental and societal damage. For example, the US’s 1954 Castle Bravo test, conducted in secret at Bikini Atoll in the Marshall Islands, delivered large volumes of radioactive fallout to several nearby islands and their inhabitants.

Between 1952 and 1957, the UK conducted several tests in Australia, scattering long-lived radioactive material over wide areas of South Australian bushland, with devastating consequences for local Indigenous communities.

In 1963, the US, the UK and the USSR agreed to carry out future tests underground to limit fallout. Nevertheless, testing continued unabated as China, India, Pakistan and North Korea also entered the fray over the following decades.

How to spot an atom bomb

During this period there were substantial international efforts to figure out how to monitor nuclear testing. The competitive nature of weapons development means much research and testing is conducted in secret.

Groups such as the Comprehensive Nuclear-Test-Ban Treaty Organization today run global networks of instruments specifically designed to identify any potential tests. These include:

• air-testing stations to detect minute quantities of radioactive elements in the atmosphere
• aquatic listening posts to hear underwater tests
• infrasound detectors to catch the low-frequency booms and rumbles of explosions in the atmosphere
• seismometers to record the shaking of Earth caused by underground tests.

A needle in a haystack

Seismometers are designed to measure seismic waves: tiny vibrations of the ground surface generated when large amounts of energy are suddenly released underground, such as during earthquakes or nuclear explosions.

There are two main kinds of seismic waves. First are body waves, which travel outwards in all directions, including down into the deep Earth, before returning to the surface. Second are surface waves, which travel along Earth’s surface like ripples spreading out on a pond.

The Comprehensive Test-Ban-Treaty Organization uses seismic stations to monitor the globe for underground nuclear explosions.

The difficulty in using seismic waves to monitor underground nuclear tests is distinguishing between explosions and naturally occurring earthquakes. A core goal of monitoring is never to miss an explosion, but there are thousands of sizeable natural quakes around the world every day.

As a result, monitoring underground tests is like searching for a potentially non-existent needle in a haystack the size of a planet.

Nukes vs quakes

Many different methods have been developed to aid this search over the past 60 years.

Some of the simplest include analysing the location or depth of the source. If an event occurs far from volcanoes and plate tectonic boundaries, it might be considered more suspicious. Alternatively, if it occurs at a depth greater than say three kilometres, it is unlikely to have been a nuclear test.

However, these simple methods are not foolproof. Tests might be carried out in earthquake-prone areas for camouflage, for example, and shallow earthquakes are also possible.

A more sophisticated monitoring approach involves calculating the ratio of the amount of the energy transmitted in body waves to the amount carried in surface waves. Earthquakes tend to expend more of their energy in surface waves than explosions do.

This method has proven highly effective for identifying underground nuclear tests, but it too is imperfect. It failed to effectively classify the 2017 North Korean nuclear test, which generated substantial surface waves because it was carried out inside a tunnel in a mountain.

This outcome underlines the importance of using multiple independent discrimination techniques during monitoring – no single method is likely to prove reliable for all events.

An alternative method

In 2023, my colleagues and I from the Australian National University and Los Alamos National Laboratory in the US got together to re-examine the problem of determining the source of seismic waves.

We used a recently developed approach to represent how rocks are displaced at the source of a seismic event, and combined it with a more advanced statistical model to describe different types of event. As a result, we were able to take advantage of fundamental differences between the sources of explosions and earthquakes to develop an improved method of classifying these events.

We tested our approach on catalogues of known explosions and earthquakes from the western United States, and found that the method gets it right around 99% of the time. This makes it a useful new tool in efforts to monitor underground nuclear tests.

Robust techniques for identification of nuclear tests will continue to be a key component of global monitoring programs. They are critical for ensuring governments are held accountable for the environmental and societal impacts of nuclear weapons testing.

Mark Hoggard, DECRA Research Fellow, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→February 21, 2024

Was going to space a good idea?

NASA Alice Gorman, Flinders UniversityIn 1963, six years after the first satellite was launched, editors from the Encyclopaedia Britannica posed a question to five eminent thinkers of the day: “Has man’s conquest of space increased or diminished his stature?” The respondents were philosopher Hannah Arendt, writer Aldous Huxley, theologian Paul Tillich, nuclear scientist Harrison Brown and historian Herbert J. Muller.

Sixty years later, as the rush to space accelerates, what can we learn from these 20th-century luminaries writing at the dawn of the space age?

The state of space 60 years on

Much has happened since. Spacecraft have landed on planets, moons, comets and asteroids across the Solar System. The two Voyager deep space probes, launched in 1977, are in interstellar space.

A handful of people are living in two Earth-orbiting space stations. Humans are getting ready to return to the Moon after more than 50 years, this time to establish a permanent base and mine the deep ice lakes at the south pole.

Water ice in the permanently shadowed craters of the lunar south pole. NASA/Goddard Space Flight Center Scientific Visualization Studio. Data from JAXA/Selene

There were only 57 satellites in Earth orbit in 1963. Now there are around 10,000, with tens of thousands more planned.

Satellite services are part of everyday life. Weather prediction, farming, transport, banking, disaster management, and much more, all rely on satellite data.

Despite these tremendous changes, Arendt, Huxley and Tillich, in particular, have some illuminating insights.

A brave new world

Huxley is famous for his 1932 dystopian science fiction novel Brave New World, and his experimental use of psychedelic drugs.

In his essay, he questioned who this “man” who had conquered space was, noting it was not humans as a species but Western urban-industrial society that had sent emissaries into space.

This has not changed. The 1967 Outer Space Treaty says space is the province of all humanity, but in reality it’s dominated by a few wealthy nations and individuals.

Huxley said the notion of “stature” assumed humans had a special and different status to other living beings. Given the immensity of space, talking of conquest was, in his opinion, “a trifle silly”.

Tillich was a theologian who fled Nazi Germany before the second world war. In his essay he wrote about how seeing Earth from outside allowed us to “demythologise” our planet.

In contrast to the much-discussed “overview effect” which inspires astronauts with a feeling of almost mystical awe, Tillich argued that the view from space made Earth a “large material body to be looked at and considered as totally calculable”.

An image of the lunar surface taken by the US Ranger 7 spacecraft in 1964. NASA/JPL-Caltech

When spacecraft began imaging the lunar surface in the 1960s, the process of calculation started for the Moon. Now, its minerals are being evaluated as commodities for human use.

Have humans changed, or is it how we view Earth?

Like Tillich, Arendt left Germany under the shadow of Nazism in 1933. She’s best remembered for her studies of totalitarian states and for coining the term “the banality of evil”.

Her essay explored the relationship between science and the human senses. It’s a dense and complex piece; almost every time I read it, I come away with something different.

In the early 20th century, Einstein’s theory of special relativity and quantum mechanics showed us a reality far beyond the ability of our senses to comprehend. Arendt said it was absurd to think such a cosmos could be “conquered”. Instead, “we have come to our present capacity to ‘conquer space’ through our new ability to handle nature from a point in the universe outside the earth”.

The new geocentrism

The short human lifespan and the impossibility of moving faster than the speed of light mean humans are unlikely to travel beyond the Solar System. There is a limit to our current expansion into space.

When that limit is reached, said Arendt, “the new world view that may conceivably grow out of it is likely to be once more geocentric and anthropomorphic, although not in the old sense of the earth being the center of the universe and of man being the highest being there is”. Humans would turn back to Earth to make meaning of their existence, and cease to dream of the stars.

This new geocentrism may be exacerbated by an environmental problem already emerging from the rapid growth of satellite megaconstellations. The light they reflect is obscuring the view of the night sky, cutting our senses off from the larger cosmos.

The far future

But what if it were technologically possible for humans to expand into the galaxy?

Arendt said assessing humanity from a position outside Earth would reduce the scale of human culture to the point at which humans would become like laboratory rats, studied as statistical patterns. From far enough away, all human culture would appear as nothing more than a “large scale biological process”.

Arendt did not see this as an increase in stature:

The conquest of space and the science that made it possible have come perilously close to this point [of seeing human culture as a biological process]. If they ever should reach it in earnest, the stature of man would not simply be lowered by all standards we know of, but have been destroyed.

Sixty years on, nations are competing to exploit lunar and asteroid mineral resources. Private corporations and space billionaires are increasingly being touted as the way forward. After the Moon, Mars is the next world in line for “conquest”. The contemporary movement known as longtermism promotes living on other planets as insurance against existential risk, in a far future where humans (or some form of them) spread to fill the galaxies.

But the question remains. Is space travel enhancing what we value about humanity? Arendt and her fellow essayists were not convinced. For me, the answer will depend on what values we choose to prioritise in this new era of interplanetary expansion.

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This article developed from a panel discussion at the Wheeler Centre. You can listen to it here.

Alice Gorman, Associate Professor in Archaeology and Space Studies, Flinders University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→December 05, 2023