We characterize the seismic events that occurred in North Korea on 9 September 2016 and South Korea on 12 September 2016. The 9 September 2016 event was identified as an explosion, and the two 12 September 2016 events were identified as natural earthquakes using the P/S (P‐ and S‐wave) spectral ratios, Pg/Lg, Pn/Lg, and Pn/Sn as discriminants. The explosive event was relocated within the North Korean nuclear test site using a relative location method and the 2006 North Korea underground nuclear test as the master event, and the epicenter was identified at 41.2976° N latitude and 129.0804° E longitude. From the regional Lg and Rayleigh waves, the body‐ and surface‐wave magnitudes for the 9 September 2016 event were calculated as mb(Lg)=4.8±0.2 and Ms=4.2±0.1. By adopting an empirical magnitude–yield relation for the body‐wave magnitude, and assuming that the explosion was fully coupled and detonated at a normally scaled depth, we estimated that the seismic yield was 6  kt, and the uncertainty range was between 3 and 11 kt. If an overburied depth range between 780 and 1200 m was applied, then the yield would be increased to 16–22 kt.

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