An underground nuclear explosion in North Korea from early September 2017 moved a mountain, according to new research. The most recent nuclear weapons detonation happened inside the country's high-security mountain test site, causing the peaks of the mountain to travel upwards and then outwards by several meters.
This is the first time there's been a combined satellite radar imaging and seismic analysis of the blast at Mount Mantap. The new study also determined that the seismic activity clocked in at an impressive 6.3 magnitude, which also caused the mountain's top to sink in by half a meter.
"I have mapped surface displacement from many geodynamic processes such as earthquakes, volcano eruptions, landslides, but I have never seen such a large displacement caused by human activity," said study co-author Teng Wang, a remote-sensing and geodesy researcher at Nanyang Technological University in Singapore.
The Democratic People's Republic of North Korea became the first country to remove themselves from the Treaty on the Non-Proliferation of Nuclear Weapons in 2003, despite upholding the treaty since 1968. In 2006, the country started nuclear testing. These activities culminated in the September 3, 2017 display of its sixth test -- and its most powerful nuclear device yet. Unconfirmed reports suggested that the mighty explosion collapsed a tunnel shortly after the test, killing hundreds of workers inside the mountain.
Researchers involved in the most recent analysis said the study used techniques normally involved in making 3D terrain maps. However, they hope making the technique more popular could help geophysicists collect data to supplement traditional seismic models and monitor future nuclear tests around the world.
"Nuclear tests are not common these days," said Matt Wei, a geophysicist at the University of Rhode Island in Narragansett. "However, monitoring nuclear tests is still one of the most important things that we do."
In total, the international team of geophysicists estimated the bomb's power was equivalent to roughly 190 kilotonnes of TNT. For context, that's 13 times more powerful than the bomb that was dropped on Hiroshima, Japan during WWII. This recent analysis actually comes in higher than the bomb's initial power estimates.
“We have never seen such large displacement caused by human activity via SAR imagery,” said Douglas Dreger, a scientist at the Department of Earth and Planetary Science, University of California-Berkeley and a co-author of the study. “But the vertical displacement is much smaller comparing to the horizontal displacement. We later figured out that this is due to the gravity-driven compaction after the explosion.”
There have also been two different studies from Chinese research teams since the bomb's detonation that suggest that the mountain's partial collapse could compromise it entirely and could be leaking radiation. While the new study doesn't speak to whether the site is still usable, it does give geologists around the world new technologies with which to track future detonations.
"The radar information really seems to help create a more accurate picture of what happened at the test site," said David Albright, president of the non-governmental Institute for Science and International Security, who was not involved in the study.
This information was published in the most recent edition of the journal Science.