资源环境科技发展态势分析平台

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 degrees-75 degrees and an azimuth of similar to 150 degrees, 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 degrees-90 degrees. The occurrence of the on-site collapse calls for continued monitoring of any leaks of radioactive materials from the test site.