ABSTRACT

Examination of regional distance seismic data from historic nuclear test sites has led to a variety of very effective discriminants between explosions, earthquakes, and collapses. We focus on the body‐wave methods. We show that ratios between P‐ and S‐wave amplitudes (P/S ratios) above about 2  Hz very effectively separate the six Democratic People’s Republic of Korea (DPRK) declared nuclear tests between 2006 and 2017 from natural earthquakes in the region. Similarly, P/S ratios separate historic Nevada Test Site (NTS) nuclear explosions from western U.S. earthquakes. We show that combining P/S ratios with ratios of low‐frequency to high‐frequency S‐wave amplitudes can effectively separate postexplosion collapse events, such as the 1982 NTS Atrisco collapse, and the apparent collapse that followed about eight and a half minutes after the 3 September 2017 DPRK explosion. Explosions often produce fewer and smaller aftershocks than comparably sized earthquakes, which has been proposed as a potential discriminant. We apply the body‐wave techniques to the recent seismicity following the largest DPRK event, after first using correlation methods to build a more complete catalog of these events. Despite the empirical effectiveness of the regional body‐wave discriminants, the physical basis for the generation of explosion S waves, and therefore the predictability of P/S and low/high frequency techniques, as a function of path, frequency, and event properties such as size, depth, and geology, remains incompletely understood. A goal of current research, such as the Source Physics Experiments (SPE), is to improve our physical understanding of the mechanisms of explosion S‐wave generation and advance our ability to numerically model and predict them.

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