The North Korean nuclear explosion test site in Punggye-ri is located in a seismically quiescent region on a stable Precambrian basement. The 3 September 2017 M W 5.6 North Korean underground nuclear explosion (UNE) test produced unprecedented strong ground motions. The peak ground accelerations might reach tens to hundreds m/s 2 on the surface of the UNE test site, decaying exponentially with distance. Ten shallow events with magnitudes greater than or equal to M L 2.5 and source depths less than 3 km followed the 2017 UNE for 5 months in an area with a radius of 15 km from the UNE where strong ground shaking was experienced. The largest event with M W 3.7 occurred 20 days after the 2017 UNE test at shallow depths less than 3 km. Its moment tensor solution indicates a combined source behavior with comparable strengths of double-couple and compensated linear vector dipole (CLVD) components, suggesting an unusual event different from typical natural earthquakes in the Korean Peninsula. The clustered shallow seismic events appeared to have occurred in damaged media that were effectively perturbed by the strong ground motions of the UNE.
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We are grateful to two reviewers for their valuable comments that improved the presentation of the paper. The analysis results from the processed data are presented in the supporting information. The seismic waveforms and station information are available with permission from the Korea Meteorological Administration (http:// www.kma.go.kr/) and Korea Institute of Geoscience and Mineral Resources (http://www.kigam.re.kr/). This work was supported by the Korea Meteorological Administration Research and Development Program under Grant KMI2018-02910. In addition, this research was partly supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1A6A1A07015374).
© 2019, The Author(s).
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