Seismic instruments: article

Аnnotation: The results of the analysis of the aftershock sequences initiated by the underground nuclear tests conducted in North Korea in 2016 and 2017 are presented. Waveform cross-correlation and a multi-master method applied to phase association allowed us to find and analyze almost 100 aftershocks and divide them into two clusters related to the underground explosions con-ducted on 09.09.2016 (DPRK-5) and on 03.09.2017 (DPRK-6). The duration, intensity, and sporadic nature of these two sequences indicate specific mechanisms of seismic energy release, probably related to the interaction of the destruction zones of the DPRK-5 and DPRK-6 ex-plosions and the collapse of their cavities with the gradual advance of the collapse column to the free surface. The aftershock activity in 2021 allows assuming the collapse process is not yet completed and expecting new after-shocks in the near future, which could end in the collapse column reaching the free surface. These assump-tions were confirmed – during the preparation of the article, on 11.02.22, a strong aftershock with a magnitude of 3.85 was recorded, which, according to preliminary estimates, indicates the beginning of the final stage of the collapse, the probability of which is discussed in this study.