Three-Dimensional Surface Deformation Related to the 2017 North Korea Nuclear Test Observed by Sar Offset-Tracking Approach

North Korea conducted the sixth nuclear test in Punggye-ri on 3 September 2017. An artificial earthquake of Mw 6.3 was reported near North Korea's Punggye-ri nuclear test site. Several minutes later, a second smaller earthquake followed the initial event, and it was characterized as a collapse of the cavity. The large and complex deformations related to the earthquakes occurred in the ground surface. It is very important to measure the artificial earthquake-related deformations, because it enables us to estimate the location, depth and cavity radius of the nuclear test. We observed the three-dimensional surface deformations related to the sixth North Korea nuclear test using the ascending and descending ALOS-2 PALSAR-2 radar offset-tracking. We used the multi-kernel offset tracking method to improve the precision of the offset-tracking measurement. The maximum deformation of more than 3 m was observed in the horizontal direction. We estimated the location, depth and cavity radius using the Mogi model. The estimated depth and cavity radius are about 600 m and about 52 m, respectively. The satellite offset-tracking observation will contribute to the nuclear test monitoring and characterization.