ABSTRACT

The most recent declared nuclear test (DPRK‐6) at the North Korean Punggye‐ri nuclear test site was an order of magnitude larger than any of the previous explosions, and for the first time was accompanied by additional seismicity large enough to be observed at regional distances. The first such event was a collapse about 8.5 min after the explosion, and this was followed by three earthquakes over the next several weeks. In this work, signals from these earthquakes recorded at four stations were used to build subspace detectors, which were then used to scan the available data for previously unobserved events near the test site. The time period scanned extends from early 2009 until March 2018, and in that time four explosions, the collapse event, the three template events, and 30–37 additional template‐matched events were detected. (Seven of the detections are low‐reliability single‐station detections at station MDJ.) Most of the events occurred within the weeks following DPRK‐6. Thirteen of the detected events have been located. These events form two clusters, both to the northwest of the test site. The first cluster is about 3 km from the test site and contains an event that occurred in 2016 (before DPRK‐5) as well as two of the last events detected in this work. The second cluster is about 6 km northwest of the test site and contains only events that occurred after the last test. Both clusters appear to be quite compact. The north–south extent of the clusters is well constrained by the observations to be less than 1–2 km. Moreover, the relatively high correlation coefficients in the 2–8 Hz band also argue for small separations between events. These events are hypothesized to have occurred on a northwest‐striking fault plane that passes near or under the Punggye‐ri test site. High stress state (inferred from low b‐values) supports the idea that each cluster is located at an asperity on the hypothesized fault plane. Prior to DPRK‐3, no events were observed from either cluster, but since DPRK‐3 there has been at least one event per year. This is consistent with stress change triggering behavior observed elsewhere and suggests that all these events were triggered by stress changes on the asperities due to the explosions.

You do not currently have access to this article.