Abstract
North Korea’s 3 September 2017 nuclear test was followed by several small seismic events, with one eight‐and‐a‐half minutes after the test and three on and after 23 September 2017. Seismic analysis reveals that the first event is a near vertical on‐site collapse toward the nuclear test center from 440 ± 260 m northwest of the test site, with its seismic source best represented by a single force with a dip angle of 70°–75° and an azimuth of ~150°, and the later events are an earthquake swarm located 8.4 ± 1.7 km north of the test site within a region of 520 m, with a focal depth of at least 2.4 km and a focal mechanism of nearly pure strike slip along the north‐south direction with a high dip angle of 50°–90°. The occurrence of the on‐site collapse calls for continued monitoring of any leaks of radioactive materials from the test site.
