The Comprehensive Test Ban Treaty Organistation (CTBTO)  (https://www.ctbto.org/the-treaty/developments-after-1996/2016-sept-dprk-announced-nuclear-test/) based in Vienna and e.g. the USGS (earthquake.usgs.gov/earthquakes/eventpage/us10006n8a) earthquake service registered an unconventional seismic event at the known nuclear test site in North Korea, showing the characteristics of an explosion. However, whether the explosion was in fact of nuclear origin cannot be determined from seismic recordings alone.

Just as for the January test, the seismic waves created by tonights test were measured by the temporary AlpArray stations deployed by the University of Vienna in Austria and Slovakia (see Figure). The recorded waveforms reveal a striking similarity between the event from January 2016 and today. While the shape of the waveforms is almost identical, the event from tonight induced sligtly stronger ground motion. This suggests very similar source mechanisms for the two tests and indicated that the explosion from September 9, 2016 was slightly stronger than the one from January 2016.