Could the seismic signal from an underground nuclear explosion be concealed by the seismic waves of a natural earthquake? A new review article published in the Bulletin of the Seismological Society of America challenges long-held assumptions about the phenomenon known as explosion masking.
Joshua Carmichael and colleagues at Los Alamos National Laboratory analyzed how even advanced signal detection technology struggles when seismic signals from a nuclear test are overlapped by earthquake signals. Their study found that while a state-of-the-art detector could identify a 1.7-ton buried explosion with 97% accuracy under normal conditions, that success rate dropped to just 37% when the explosion occurred within 100 seconds and roughly 250 kilometers of a natural earthquake.
"The overlapping waveforms of an explosion and an earthquake obscure even the most sensitive digital detectors’ ability to identify an explosion," said Carmichael.
These findings could prompt experts to reconsider a 2012 report that had concluded earthquake signals could not mask explosion signals. Explosion masking poses a significant concern for scientists tasked with monitoring nuclear tests worldwide.
In regions like North Korea, where six nuclear tests have occurred in the past two decades, increased seismic monitoring has revealed much more low-magnitude seismicity near test sites than previously known, Carmichael noted.
The study suggests that in any seismically active region, background seismic activity could significantly lower the likelihood of detecting underground explosions. Carmichael and his team also found that natural events like earthquake swarms or repeating seismic activity could similarly mask signals, dropping detection rates from 92% to just 16%.
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"This suggests we may be undercounting the number of earthquakes during swarms or aftershock sequences," Carmichael said.
Testing the explosion masking theory has been challenging due to a lack of real-world data containing both explosion and natural seismic signals. Simulating explosion data has proven difficult because of uncertainties around the high-frequency signals from smaller explosions.
Instead, the researchers used actual explosion and natural seismicity data from the Nevada National Security Site. They scaled down the amplitude of explosion data to mimic smaller events and then injected these waveforms into earthquake data to see if sophisticated multi-channel correlation detectors could still identify them.
This method created a dense dataset that allowed the researchers to rigorously test the idea that natural seismicity could hide explosion signals.
While seismic monitoring is not the only tool used to detect nuclear tests—scientists also monitor for atmospheric radionuclides—the study offers a new framework for calculating the likelihood of detecting explosions based on seismic data alone. According to Carmichael, the results provide an important step in improving nuclear test monitoring capabilities by integrating seismic probabilities with other detection methods.
Joshua Carmichael and colleagues at Los Alamos National Laboratory analyzed how even advanced signal detection technology struggles when seismic signals from a nuclear test are overlapped by earthquake signals. Their study found that while a state-of-the-art detector could identify a 1.7-ton buried explosion with 97% accuracy under normal conditions, that success rate dropped to just 37% when the explosion occurred within 100 seconds and roughly 250 kilometers of a natural earthquake.
"The overlapping waveforms of an explosion and an earthquake obscure even the most sensitive digital detectors’ ability to identify an explosion," said Carmichael.
These findings could prompt experts to reconsider a 2012 report that had concluded earthquake signals could not mask explosion signals. Explosion masking poses a significant concern for scientists tasked with monitoring nuclear tests worldwide.
In regions like North Korea, where six nuclear tests have occurred in the past two decades, increased seismic monitoring has revealed much more low-magnitude seismicity near test sites than previously known, Carmichael noted.
The study suggests that in any seismically active region, background seismic activity could significantly lower the likelihood of detecting underground explosions. Carmichael and his team also found that natural events like earthquake swarms or repeating seismic activity could similarly mask signals, dropping detection rates from 92% to just 16%.
https://www.kumander.org/viewtopic.php?t=236
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"This suggests we may be undercounting the number of earthquakes during swarms or aftershock sequences," Carmichael said.
Testing the explosion masking theory has been challenging due to a lack of real-world data containing both explosion and natural seismic signals. Simulating explosion data has proven difficult because of uncertainties around the high-frequency signals from smaller explosions.
Instead, the researchers used actual explosion and natural seismicity data from the Nevada National Security Site. They scaled down the amplitude of explosion data to mimic smaller events and then injected these waveforms into earthquake data to see if sophisticated multi-channel correlation detectors could still identify them.
This method created a dense dataset that allowed the researchers to rigorously test the idea that natural seismicity could hide explosion signals.
While seismic monitoring is not the only tool used to detect nuclear tests—scientists also monitor for atmospheric radionuclides—the study offers a new framework for calculating the likelihood of detecting explosions based on seismic data alone. According to Carmichael, the results provide an important step in improving nuclear test monitoring capabilities by integrating seismic probabilities with other detection methods.
