Abstract
Abstract. On 3 September 2017 official channels of the Democratic People's Republic of Korea announced the successful test of a thermonuclear device. Only seconds to minutes after the alleged nuclear explosion at the Punggye-ri nuclear test site in the mountainous region in the country's northeast at 03:30:02 (UTC), hundreds of seismic stations distributed all around the globe picked up strong and distinct signals associated with an explosion. Different seismological agencies reported body wave magnitudes of well above 6.0, consequently estimating the explosive yield of the device on the order of hundreds of kT TNT equivalent. The 2017 event can therefore be assessed as being multiple times larger in energy than the two preceding North Korean events in January and September 2016. This study provides a multi-technology analysis of the 2017 North Korean event and its aftermath using a wide array of geophysical methods. Seismological investigations locate the event within the test site at a depth of approximately 0.6 km below the surface. The radiation and generation of P- and S-wave energy in the source region are significantly influenced by the topography of the Mt. Mantap massif. Inversions for the full moment tensor of the main event reveal a dominant isotropic component accompanied by significant amounts of double couple and compensated linear vector dipole terms, confirming the explosive character of the event. The analysis of the source mechanism of an aftershock that occurred around 8 min after the test in the direct vicinity suggest a cavity collapse. Measurements at seismic stations of the International Monitoring System result in a body wave magnitude of 6.2, which translates to an yield estimate of around 400 kT TNT equivalent. The explosive yield is possibly overestimated, since topography and depth phases both tend to enhance the peak amplitudes of teleseismic P waves. Interferometric synthetic aperture radar analysis using data from the ALOS-2 satellite reveal strong surface deformations in the epicenter region. Additional multispectral optical data from the Pleiades satellite show clear landslide activity at the test site. The strong surface deformations generated large acoustic pressure peaks, which were observed as infrasound signals with distinctive waveforms even at distances of 401 km. In the aftermath of the 2017 event, atmospheric traces of the fission product 133Xe were detected at various locations in the wider region. While for 133Xe measurements in September 2017, the Punggye-ri test site is disfavored as a source by means of atmospheric transport modeling, detections in October 2017 at the International Monitoring System station RN58 in Russia indicate a potential delayed leakage of 133Xe at the test site from the 2017 North Korean nuclear test.
Highlights
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) and its associated entity, the Preparatory Commission for the CTBT organization (CTBTO), are dedicated to monitoring and banning nuclear explosions worldwide – underground, in water, or in the atmosphere
– The explosive character of the 3 September 2017 North Korean event is confirmed by moment tensor inversion (MTI) analysis
– The aftershock directly following the nuclear explosion has a similar depth as the test and can be characterized as a collapse of the cavity created by the test
Summary
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) and its associated entity, the Preparatory Commission for the CTBT organization (CTBTO), are dedicated to monitoring and banning nuclear explosions worldwide – underground, in water, or in the atmosphere. From a scientific point of view, the depth of the event, its strength in terms of radiated high- and low-frequency seismic energy, the contribution of possible faulting or slope instability processes, the near-surface damage in the test area, and the proof of whether fission products are detected as atmospheric tracers are key questions to be answered These questions are approached by an integrated study based on different seismological As there is no easy concept to verify and characterize nuclear explosions, especially in a country where direct observations are difficult to assess, this study demonstrates and emphasizes the strength of an integrated multi-technology approach In this context, new methodical approaches are introduced to improve the depth estimate from teleseismic observations and to quantify uncertainties in the non-isotropic source component. While radionuclide monitoring provides the only direct evidence of nuclear explosions, it is demonstrated by careful modeling how difficult it is to interpret such data and that early claims of causal anomalies have possibly been over-interpreted
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