固物研究生论坛 - A crustal P-velocity model

The large yield nuclear test conducted by Democratic People’s Republic of Korea (DPRK) (North Korea) on September 3, 2017 registered high-quality seismic waveforms at nearby seismic stations. The source time function and radiation pattern of nuclear explosions are much simpler than natural earthquakes, thus providing a good opportunity to study the crustal structure. The crustal model of China-North Korea border region can provide an initial model for a three-dimensional model and can be of importance for the source analysis of North Korea nuclear tests. High-precision location result shows that the absolute geographic location of this nuclear test is (129.0745 °N，41.3006 °E), with an error of 200 meters. By waveform modeling and travel time analysis of the seismic data recorded by broadband seismic stations in Northeast China, we obtain a crustal P-velocity model of the China-DPRK border region. The crustal structure can be represented by a two-layered model with a constant velocity in the upper crust and a gradient velocity in the lower crust. The P wave velocity of the upper crust is estimated to be 6.1 km/s by fitting the absolute travel times of the Pg phases, the P wave velocity of the uppermost mantle is 8.019 km/s based on the absolute Pn wave arrival times and the velocity gradient in the lower crust is inferred based on the indiscernible Moho PmP reflections in the seismic data. An additional discontinuity may exist below the Moho in some regions of the uppermost mantle, to account for the large amplitude of Pn waves observed in some stations.