Collapse and Earthquake Swarm After North Korea's 3 September 2017 Nuclear Test

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.Plain Language Summary On 3 September 2017, the Democratic People's Republic of Korea (North Korea) announced that it had successfully conducted a thermonuclear (hydrogen bomb) test. The nuclear test was followed by several reported small seismic events occurring in the region. While there have been intense interests and concerns about what has happened after the nuclear test among the scientific community, governmental agencies, and the public, the nature of those events is unknown. In this study, we present high-precision relative locations and detailed source characteristics of the small events following the test. Seismic analysis reveals that the first event occurring eight-and-a-half minutes after the test is a near vertical on-site collapse toward the nuclear test center from 440 ± 260 m northwest of the nuclear test site, with its seismic source best represented by a near vertical single force, and the later three events on and after 23 September 2017 are an earthquake swarm located 8.4 ± 1.7 km north of the nuclear test site within a region of 520 m, with an event depth of at least 2.4 km. The occurrence of the on-site collapse calls for continued monitoring of any leaks of radioactive materials from the test site.

The rise, collapse, and compaction of Mt. Mantap from the 3 September 2017 North Korean nuclear test

“…The divergent horizontal motions and the moment tensor of the first event consistently suggest a predominant isotropic explosive source buried at shallow depth. The moment of the geodesy-derived models, assuming an empirical rigidity of 5.7 GPa (36), is M w = 5.5, larger than the one inferred seismically (M w = 5.24), because it includes slow deformation that did not generate seismic waves, with a total volume change of 0.01 km 3 . The seismic analysis of the second event reveals an implosive seismic source that occurred south of the first event with a dominant negative isotropic component, suggesting an inverse process of the main explosion.…”

Seismic Constraints on the Magmatic System Beneath the Changbaishan Volcano: Insight Into its Origin and Regional Tectonics

“…These nuclear tests have led to the question of whether the dynamic stress changes are large enough to disturb the magma chambers beneath the volcano and therefore accelerate the volcanic activity (Hong et al, ) or trigger microseismicity around the volcano (Liu, Li, Peng, et al, ). A recent study by Tian et al () reported that the North Korea's 3 September 2017 nuclear test has triggered an earthquake swarm with a maximum magnitude of 3.6 located ~8.4 km to the north of the test site.…”

Seismic detection of strong ground motions by MW5.6 North Korean nuclear explosion

“…The inverted vertical source location of the 6th UNE is 597 m above the sea level, which corresponds to 1611 m below the surface considering the topography of the source region 21 . The inverted detonation depth of the 6th UNE is close to the elevation of tunnel entrance (~1400 m above the sea level and ~760 m below the surface), supporting the depth accuracy of the hypocenter-inversion method 10 .…”