A seismo-acoustic analysis of the 2017 North Korean nuclear test

The 2017 North Korean nuclear test gave rise to seismic and low-frequency acoustic signals, i.e. infrasound. The infrasonic signals are due to seismo-acoustic coupling and have been detected on microbarometer array I45RU in the Russian Federation at 401 km from the test site. I45RU is part of the International Monitoring System for the verification of the Comprehensive Nuclear Test-Ban-Treaty. We analyze the seismo-acoustic coupling by making use of array processing and back projection techniques. The back projections show, that infrasound is radiated from a much larger region than was previously expected. These regions are found to be consistent with the locations of topography and sedimentary basins. The back projections can be used to estimate the average infrasonic propagation speed through the atmosphere. We discuss these findings in the context of infrasound propagation conditions during the sixth nuclear test. It is suggested that propagation from the test site to I45RU may have occurred along unexpected paths instead of typical stratospheric propagation. We present several scenarios that could be considered in the interpretation of the observations.