Seismic and ionospheric disturbances caused by the 3 September 2017 underground nuclear test in North Korea

We investigated lithospheric and ionospheric disturbances caused by the 3 September 2017 underground nuclear test (UNT) in North Korea based on data from networks of seismic stations and GPS/GLONASS receivers. We analyzed frequency composition of longitudinal and surface waves detected at more than 40 seismic stations. Low frequencies (∼0.45 ± 0.21 Hz) were found to prevail in the spectrum of longitudinal waves. For both types of waves, frequencies decreased with distance according to the power law. Analysis revealed two trends in the spatial distribution of peak frequencies. First, high and mid-frequencies (0.14–0.50 Hz) are typical for the continental landmass regions, and low frequencies of surface waves (0.13 Hz and below) are more common for the regions adjacent to fringe seas. Second, uneven frequency variations of seismic waves for different azimuths relative to the UNT epicenter (frequencies subside rapidly in the east, southeast, and southwest directions from the epicenter; towards the continental landmass inner parts, frequency variation is much slower). Records of longitudinal waves made at different distances from the epicenter allowed estimating the size of the focal area. Analysis of data from GPS/GLONASS receiving stations near the Korean Peninsula revealed ionospheric disturbances that were most likely caused by UNT. The ionospheric disturbances started to be detected ∼ 8 min after UNT and were observed for about 5 hrs. During the first 1.5–2 hrs after UNT, travelling ionospheric disturbances (TID) were recorded; they propagated from the epicenter at ∼ 600, 250 and 133 m/s. These TIDs had periods of 1–10.5 min and could be associated with acoustic waves induced in the Earth's atmosphere by the underground nuclear test. After TID passage over the UNT site, there was a long-lived (more than 3.5 hrs) region of non-travelling perturbations of ionospheric plasma with the velocity about 7 m/s. This velocity describes not so much the disturbance travel, but the time when the "receiver – satellite" line of sight (LOS) crosses the disturbance. This region can possibly occur due to the formation of standing waves in the atmosphere, development of plasma instabilities or penetration into the ionosphere of an anomalous electric field generated by radioactive substances leaked out onto the surface.