The 9 September 2016 North Korean underground nuclear test

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 degrees N latitude and 129.0804 degrees 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+ or -0.2 and Ms=4.2+ or -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 approximately 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.