Probing the DPRK nuclear test-site down to low seismic magnitude

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1785/0220180116. This is version 1 of this Preprint.

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Authors

Steven John Gibbons , Tormod Kværna, Sven Peter Näsholm, Svein Mykkeltveit

Abstract

On 3 September 2017, the Democratic People’s Republic of Korea (DPRK) carried out its sixth declared underground nuclear test (NK6) at the Punggye‐ri test site. With body‐wave magnitude 6.1, this explosion was significantly larger than any of the previous five explosions, and it has been followed by numerous smaller seismic events. The explosion generated seismic waves dominated by significantly lower frequencies than the earlier tests, which makes accurate measurement of relative time delays using cross‐correlation challenging. Finding a frequency band at which one observes common features in the NK6 signals and the corresponding signals from an earlier event can result in reduced signal‐to‐noise ratio (SNR). Classical double‐difference location estimates for NK6 show a significant spread, depending on the set of measurements used. We treat the first five declared DPRK explosions as a source array and demonstrate, using a geometrical argument about the relative time shifts visible between the signals on pairs of stations, that NK6 was very close to the 9 September 2016 explosion (NK5), assumed to be close to the maximal overburden beneath the summit of Mount Mantap. In addition to the magnitude 4.1 presumed collapse event 8 min after NK6, numerous other small events have been observed at or close to the test site since September 2017. We demonstrate how the test site is monitored to magnitudes below two using multichannel correlation templates from all existing observations. Processing all available historical data from the KSRS and USRK arrays reveals a few small events in 2013, 2014, and 2016 that are similar in nature to those observed in late 2017. This suggests that the more recent low‐magnitude events are not simply a direct result of NK6. We urge caution in the interpretation of the correlation functions between the signals from different events at or close to the test site because the signals are a function of both the source term and of near‐source structure, with the effects of topography likely to be significant.

DOI

https://doi.org/10.31223/X58W30

Subjects

Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Keywords

Seismology, Seismic monitoring, CTBT, IMS, DPRK, North Korea, International Monitoring System, Nuclear tests, Detection Thresholds

Dates

Published: 2021-04-14 19:31

License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
No conflict of interest

Data Availability (Reason not available):
Data from the USRK, KSRS, and MJAR arrays were obtained from the International Data Center (IDC) of the Comprehensive Nuclear‐Test‐Ban Treaty Organization (CTBTO) in Vienna. The virtual data exploitation center (vDEC) at the CTBTO may provide a mechanism by which scientists not from National Data Centers can obtain access to the data. vDEC is available at https://www.ctbto.org/specials/vdec/ (last accessed July 2018).

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