theSIGNAL SCIENCE
19 September 2026
"The Earth does not forget what we do to it."
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Science

North Korea's Last Nuclear Blast Won't Stop Shaking

Seven years after North Korea's final nuclear test, Mount Mantap is still trembling — and scientists are only now understanding why.

In 2017, North Korea detonated its sixth and final underground nuclear bomb beneath Mount Mantap, a peak tucked into the remote forests of North Hamgyong province. The blast was enormous. Then, as expected, it went quiet. Except — it didn't.

The mountain kept shaking. And shaking. And shaking still. That is the startling finding of an international team led by Xingli Fan of Chengdu University of Technology, whose results were published in the journal *Science*.

The team sifted through 17 years of continuous seismic recordings — gathered between 2008 and 2025 from monitoring stations in China and South Korea — using a technique called matched-filter detection, which is sensitive enough to catch tiny tremors that standard networks routinely miss. What they found was not a fading echo. It was a crescendo. A total of 1,399 small earthquakes had occurred near the site, and the rate of shaking was actually *accelerating* toward 2025.

Photo: Romain Water / Unsplash
Seismic monitoring equipment records tremors near the North Korean nuclear test site at Mount Mantap.
Discuss
  • Why might scientists outside North Korea struggle to study seismic activity there?
  • What does the discovery of a previously unknown fault line tell us about the limits of geological mapping?
  • Should underground nuclear testing be banned purely on environmental grounds, even apart from weapons concerns?
Science

Does Gravity Treat All Particles Equally?

Drop a feather and a hammer on the Moon, and they land together. Galileo knew it. Einstein built a whole theory around it. But here is the twist: nobody has ever tested whether that rule holds for second-generation particles — the heavier, stranger cousins of ordinary matter. Physicists at ETH Zurich and the Paul Scherrer Institute in Switzerland are preparing to do exactly that. They plan to measure how muonium — a fleeting, exotic atom made of an antimuon and an electron — responds to gravity. It must be neutral, because gravity is extraordinarily weak compared with electromagnetism. Three generations of matter exist, yet nobody knows why.…
  • Should physics textbooks be rewritten if muonium defies Einstein's equivalence principle?
∞
Seismicity at Mt. Mantap continued to increase for years after the final test.
Xingli Fan, Chengdu University of Technology, lead study author
Science

Ozempic fixes blood sugar, not everything else

Millions of people take GLP-1 drugs like Ozempic and watch their blood sugar fall, their weight drop, and their cardiovascular risk shrink. But does life itself get better? University of Chicago economist Robert Kaestner tracked the same diabetic adults over a decade — and found almost no measurable change in depression, employment, or marital status after they started treatment. The a-ha moment: early differences between users and non-users vanished once researchers followed individuals over time, suggesting the drugs were attracting a certain kind of person rather than transforming one.…
  • If a drug improves your health but not your happiness, is it truly a cure?
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theSIGNAL IN THE LAB
1VOCABULARY
matched-filter detectioncrescendo
pre-existing weaknessesfleetingdetonated
sifted throughcardiovascular risk
2GRAMMAR FOCUS
Modal verbs — deduction and speculation (must have, cannot have, might have)
Use 'must have + past participle' for near-certain deductions about the past, 'cannot have + past participle' for near-certain negatives, and 'might have + past participle' for uncertain possibilities.
must have · cannot have · might have · fractured · caused · occurred · fallen · known
  1. The 2017 nuclear blast ___ the crust around pre-existing fault lines — the seismic data leaves almost no doubt.
  2. The hidden fault near Mount Mantap ___ appeared on any map before the study, since researchers describe it as entirely new.
  3. Scientists ___ that the rate of earthquakes would still be accelerating eight years after the final test.
  4. The 1,399 small earthquakes ___ randomly — their alignment along two parallel tracks is too precise for chance.
  5. If muonium falls at a different rate than ordinary matter, gravity ___ differently on second-generation particles.
  6. Early researchers ___ the seismic signals near Mount Mantap without matched-filter detection — the tremors were too small for standard networks.
3IDIOMS
Define each idiom in your own words. Then write one sentence of your own using one idiom of your choice.
  1. went quiet (article 1: 'Then, as expected, it went quiet.')
  2. a long memory (article 1: 'a mountain has a very long memory')
  3. a long grudge (article 1: 'perhaps an even longer grudge')
  4. here is the twist (article 2: 'But here is the twist')
  5. some explaining to do (article 2: 'the universe suddenly has some explaining to do')
4CRITICAL THINKING
All three articles suggest that science regularly uncovers things that contradict what experts assumed to be settled — a mountain that keeps shaking, a law of physics that may have exceptions, a drug whose benefits are narrower than believed. What does this pattern imply about the way scientific findings should be communicated to the public, and what risks arise when results are presented as final before long-term evidence exists?
5CREATIVE · HEADLINES
Write a headline for the North Korea seismic story in each of the following styles. One line each, no explanation:
  • TABLOID NEWSPAPER
  • LUXURY MAGAZINE
  • ACTIVIST BLOG
6WRITING
The Ozempic study found that researchers initially drew the wrong conclusions because they were not following the same individuals over time — only comparing groups. Choose one of the other two articles and explain how a similar flaw in research design could have led scientists to a misleading result.
7DEGREES OF EXTREMITY
Complete each ladder from mild to strong.
  • move→→
  • find→→
  • concern→→
  • decrease→→
  • problem→→
  • change→→
8SPEAKING
  1. Could the seismic acceleration near Mount Mantap ever pose danger?
  2. Why test gravity using exotic atoms rather than ordinary matter?
  3. What makes muonium especially difficult to study experimentally?
  4. Can a drug be considered successful without improving wellbeing?