Earth Observatory Blog
All Eyes and Ears: Insights from a Seismo-Geodesy Study into an Underground Nuclear Test Site
On 3 September 2017, the Democratic People’s Republic of Korea (North Korea) conducted its sixth underground nuclear test at the Punggye-ri test site. In collaboration with scientists from Germany, USA, and China, my colleagues from the Earth Observatory of Singapore (EOS) and I published our findings in Science on 11 May 2018, revealing the complex physical processes associated with the nuclear test.
We found that the top of the mountain experienced a rise, collapse, and compaction at different time scales after the explosion. The explosive yield from the nuclear detonation with seismic and geodetic modeling was between 120-304 kilotons of TNT, which is more than 10 times the power of the Hiroshima bombing (~15 kilotons).
Despite the explosion occurring in an inaccessible region, space geodesists can “see” the displacement via radar images acquired by satellites flying on the orbit 500 kilometres above the ground. By tracking the features in the satellite images acquired before and after the explosion, we were able to translate the microwave signals into surface displacements. The results showed as much as 3.5 metres (m) of divergent horizontal motion with 0.5 m of subsidence on the top of Mt. Mantap, which hosted this and four previous nuclear tests. This is the first time the complete three-dimension (3D) surface displacements associated with an underground nuclear test were imaged and presented to the public. From the modeling of the displacement data, we were able to locate the explosion precisely and determine the depth of the buried detonation.
World peace benefits from the adherence to internationally-negotiated nuclear-test-ban treaties that strive to promote the non-proliferation of nuclear weapons. Surveillance of clandestine nuclear tests relies on a global seismic network, but the potential of spaceborne monitoring has been underexploited. This study demonstrates the capability of space borne remote sensing to help characterise large underground nuclear tests, if any, in the future.