Relative Seismic Source Scaling of Pn Phases from Six North Korean Underground Nuclear Explosions
Abstract
We estimate the range of yields and source depths for the six North Korean underground nuclear explosions in 2006 (UNE06), 2009 (UNE09), 2013 (UNE13), 2016 (January; UNEJ16 and September; UNES16), and 2017 (UNE17), based on regional seismic observations in South Korea and China. Spectral ratios are calculated for event pairs using seismograms from the six explosions observed along the same paths and at the same receivers. These relative seismic source scaling spectra for Pn provide a basis for a grid search source solution that estimates source yield and depth for each event based on either the Mueller and Murphy (1971; MM71) or Denny and Johnson (1991; DJ91) source models. The grid search is used to identify the best-fit empirical spectral ratios subject to the source models by minimizing the goodness-of-fit (GOF) in the frequency range of 0.5-15 Hz. The DJ91 model produces higher ratios of depth and yield than those estimated using MM71, with significant trade-offs between depth and yield in all cases. In order to address the trade-off between depth and yield, a modified grid search was implemented that includes the propagation effects for different source depths using reflectivity Green's functions in the procedure, thus modeling slight differences in propagation path based on source depth. This revision reduces trade-offs between depth and yield, results in better model fits to frequencies as high as 15 Hz, and produces smaller GOF values than those where the depth effects of the Green's functions were ignored. These results indicate that MM71 provides comparable estimates with good agreement of spectral ratio matching long period level and corner frequency, while DJ91 estimates relatively lower yields due to a misfit in corner frequency. Based on the UNE06 estimates (depth of 250-350 m and yield of 0.8-1.5 kt), the best grid-search solutions produce depths of 450, 750, 600, 650, and 600 m and yields of 6.2, 13.0, 8.0, 20.0, and 180.0 kt for UNE09, UNE13, UNEJ16, UNES16, and UNE17, respectively.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S53E0443P
- Keywords:
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- 3355 Regional modeling;
- ATMOSPHERIC PROCESSESDE: 1040 Radiogenic isotope geochemistry;
- GEOCHEMISTRYDE: 6620 Science policy;
- PUBLIC ISSUESDE: 7219 Seismic monitoring and test-ban treaty verification;
- SEISMOLOGY