Measurement of Surface Deformation due to the 2016 Nuclear Test of North Korea Using SAR Interferometry

Underground nuclear test was performed on January 6 (01:30 UTC), 2016, at Punggye-ri Nuclear Test Site (129.049°E, 41.308°N) in North Korea. The United States Geological Survey (USGS) reported that seismic signals of a 5.1 magnitude were recorded from the location. We observed the surface deformation caused by the nuclear test using interferometric synthetic aperture radar (InSAR) technique. InSAR is a powerful method for the quantitative measurement of surface deformation, and has been widely used for inferring vital clues pertaining the source or mechanism in geologic studies. In this study, we demonstrate the surface deformation induced by the 4th nuclear test of the North Korea using high resolution L-band ALOS PALSAR data. Coseismic InSAR pairs acquired from descending and ascending orbits were used for the investigation. By the analysis of the descending pair, we obtained the deformation signals away from the satellite. The maximum displacement measured by descending data was about 13cm along the satellite's line of sight (LOS) direction. On the other hand, surface deformation measured from the ascending data enabled us to detect the movements to the opposite direction compared to the descending data. Also, we were able to decompose the horizontal and vertical displacements by integrating interferograms from both ascending and descending orbits. As a result, we confirmed that most of the surface deformation induced by the nuclear test was horizontal movements, particularly to the westward direction. It was anticipated that most of the horizontal displacements were happened by landslides as a secondary effect of the nuclear test. Weak vertical movements of about 4-5cm to the subsiding direction were also estimated, and the geometry and volumetric changes of the deformation source can be determined from these vertical signals. In conclusion, InSAR measurements will be helpful to the characterization and the better understanding about the nuclear test.