Spatio-temporal variations of short-period S waves attenuation field structure in the region of North-Korean Pungeri nuclear test site

We have been studying spatio-temporal variations of shear wave attenuation field structure in the area of North-Korean Pungeri nuclear test site. We processed recordings of underground nuclear explosions (UNEs), obtained by two stations: VLA and MDJ at distances up to 400 km. The ratios of maximum amplitudes of Lg and Pg waves for frequency of 1.25 Hz (Lg/Pg parameters) were determined. It was shown that values of Lg/Pg parameters for UNEs recordings diminished abruptly from 2006 to 2017. It is supposed that this effect is connected with ascending deep-seated fluids in the lithosphere, stipulated by intensive artificial influence of the UNEs onto the earth’s crust. It was established that mean values Lg/Pg are higher essentially for the UNEs aftershocks than for the explosions. A comparison of the attenuation field characteristics in the regions of the Pungeri and Semipalatinsk test sites is carried out.