Geodetic Signature of Nuclear Tests

NEWS: Preliminary InSAR results of the September 3, 2017 Nuclear Test [link].

Nuclear monitoring is important for national security and world peace. Recently, I used interferometric synthetic aperture radar (InSAR) data to study the nuclear tests in North Korea. North Korea conducted its fourth underground nuclear test on 2016 January 6 and its fifth on 2016 September 9. InSAR data from the Japan Aerospace Exploration Agency ALOS-2 satellite show possible deformation associated with the 2016 January 6 North Korean nuclear test whereas the European Space Agency Sentinel-1A data are decorrelated. This is the first time that deformation related to a nuclear test has been measured since 1992. In a paper published in the Geophysical Journal International, I present two interpretations of the observed deformation: First, the deformation can be explained by a triggered landslide on the western slope of Mt Mantap, with a displacement of up to 10 cm across a patch of 1 km by 1 km. Second, the observation may be from uplift created by the nuclear explosion. In the second interpretation, the location, depth and cavity size can be estimated from a topography-corrected homogenous half-space model (Mogi). The preferred location of the 2016 January 6 event is 41.2993N 129.0715E, with an uncertainty of 100 m. The estimated depth is 420–700 m and the cavity radius is 23–27 m. Based on empirical data and the assumption of granite as the host rock, the yield is estimated to be 11.6–24.4 kilotons of TNT, which is consistent with previous results based on seismic data. With these two interpretations, I demonstrate that InSAR data provide an independent tool to locate and estimate source characteristics of nuclear tests in North Korea. The ambiguity of interpretation is mainly due to the limited InSAR data acquisition. Future frequent data collection by current and upcoming InSAR satellites will allow full use of InSAR for nuclear monitoring and characterization in North Korea and around the world.

My group is actively working on improving this method for nuclear monitoring in the future.

 

Figure 1. Map of the Punggye-ri test-site region near Mt Mantap in North Korea (41.298N 129.073E). (a) Optical image as viewed on Google Earth. The lower right overlay shows the location of the test site on a larger map. The red square is the area of (d)–(f) at Mt Mantap. (b) ALOS-2 InSAR image of 2015 December 17–2016 January 14 overlays the topography in the same area of (a). The interferogram is masked at correlation of 0.1 and unwrapped. (c) ALOS-2 InSAR image between 2015 February 5 and 2016 January 7 overlays the topography in the same area as (a). The image is masked at correlation of 0.1 and unwrapped. (d)–(f) are enlarged area of (a)–(c). The green circle is the InSAR determined location for the 2016 January 6 event based on interpretation2.The other circles are estimated locations for the 2016 January 6 event from different sources based on seismic data.
Figure 2. Diagrams show the two interpretations of the InSAR data at the Punggye-ri test-site region near Mt Mantap in North Korea. (a) An optical image near the test site from Google Earth. The green circle is the InSAR determined location of the 2016 January 6 event from the second interpretation. The other circles are estimated locations for the 2016 January 6 from different sources using seismic data. (b) Diagram shows the interpretation of a triggered landslide near the test site. (c) Diagram shows the interpretation of uplift near the test site. The diagram does not scale. The uplift and cavity is exaggerated. The buried depth is f and the cavity radius is r. When the buried depth is deep and no collapse after the nuclear test, the uplift caused by the initial explosion will stay.