Relative Seismic Source Scaling Based on Pn Observations from North Korean Underground Nuclear Explosions
Abstract
Relative seismic source scaling spectra using the Pn phases along the same propagation paths and at the same receivers provide a basis for a grid search for a source solution that estimates yields and depths for each explosion pair. We estimate these parameters based on a range of source models for the six North Korean underground nuclear explosions (UNEs) in 2006, 2009, 2013, 2016 (January and September), and 2017. The Pn spectral ratios are calculated using seismograms from the six UNEs recorded at regional seismic stations in South Korea. A grid search is used to identify the best-fit empirical spectral ratios based on a collection of source models by minimizing the root mean square misfit from 0.2 to 15 Hz. Source models used in this analysis include Mueller and Murphy (1971; MM71), Denny and Johnson (1991; DJ91), and Walter and Ford (2018; WF18). To address the trade-off between depth and yield, a modified grid search using reflectivity Green's functions in the procedure was implemented to include the elastic propagation effects for different source depths. This addition reduces trade-offs between depth and yield and results in better model fits to spectral rations including frequencies as high as 15 Hz. Results from modified grid search for both the MM71 and WF18 models produce comparable source depth and yield estimates. There is good agreement between the theoretical and observed spectral ratios for these two models which match both the long period level and the corner frequency with similar yield and depth estimates. In contrast, source estimates using the DJ91 model produce lower yields due to a misfit in corner frequency.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMS049...02P
- Keywords:
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- 4430 Complex systems;
- NONLINEAR GEOPHYSICS;
- 7219 Seismic monitoring and test-ban treaty verification;
- SEISMOLOGY;
- 7270 Tomography;
- SEISMOLOGY;
- 7290 Computational seismology;
- SEISMOLOGY