Infrasound observations from the site of past underground nuclear explosions in North Korea

Abstract

Infrasound signals from the announced underground nuclear explosions at the North Korean test site were first identified in 2009 at regional infrasound stations in South Korea. For the subsequent nuclear test in 2013 corresponding arrivals were again identified at these stations, but could also be detected at the two closest IMS stations in Russia (IS45) and Japan (IS30) and were associated to the event in the Reviewed Event Bulletin of the CTBTO. When the nuclear test in January 2016 occurred and infrasound signals for IS45 were reported, it spurred this investigation of potential observations from such events conducted over the past 10 or more years. By applying F-K analyses interactively on the data of IMS infrasound stations IS45 and IS30 we verified the detections for the 2013 event, but found additional signals related to other tests except for the 2009 and September 2016 events. Additionally, we found a signal in 2009 at IS45 that we interpret as being related to the source for which a precursory signal was identified at the regional infrasound station network in South Korea. We also investigated the potential for infrasound observations for a small seismic event in May 2010 on the test site and obtained some evidence for a very weak signal. By atmospheric propagation modelling using ray tracing and parabolic equation calculations we aim at interpreting the observations and attempt to explain the corresponding arrival times of signals. As most of the signals are hidden in the background noise, we also studied the detection pattern of IS45 and IS30 in order to assess the probability of the identified signals to be random observations coming from preferred arrival directions.