DPRK Nuclear Explosion Yields from Teleseismic Modeling
[Technical Report, Final Report]
University of California Santa Cruz
Pagination or Media Count:
Seismic yields for the six declared underground nuclear tests at the North Korean test site are estimated. Absolute calibration is obtained by modeling broadband P wave ground displacements observed at teleseismic distances for the 2017 event for a granite source medium using the Mueller-Murphy explosion model, adjusting the site attenuation parameter and the pP lag time and relative amplitude in order to match the waveshapes and average amplitude. Relative to the resulting yield estimate for the 2017 event of 230 50 kt for a frequency independent average t 0.78 0.03, 4-Hz amplitude signals from the other five events are modeled using the same explosion model and attenuation operator, giving estimates in the range of 2.6 to 18.8 kt for the events from 2006 to 2016. This gives absolute-amplitude based yield estimates for all six events. The modeling uses a simple half-space or a plane-layered medium, frequency-independent attenuation, and the apparently significant effects of non-elastic behavior of the pP phase delayed in time relative to elastic predictions for the 2017 event are modeled in a simplified fashion. Broader band seismic wave estimates of the yields are obtained using short-period waveform equalization by the process of intercorrelation, involving cross-convolution with the Greens functions for two events, tied in absolute amplitude to the direct modeling results. Generally consistent relative yield estimates for the six events are obtained for a procedure that uses simple half-space media for the Greens functions and allows for non-elastic delay times of pP. Estimates of yields are in the range 1.4 to 250 kt for preferred values with burial depths constrained by event location in the mountain. Direct estimates of the Greens functions are obtained by deconvolving the source time functions from the foregoing analysis from regional broadband recordings, and layered 1D velocity structures are developed to match the deconvolved traces.
- Radiofrequency Wave Propagation