Regional Seismic Characteristics of Chemical Explosions on the Eastern Margin of the Junggar Basin, Northwest China, and of Historical Semipalatinsk Nuclear Tests

The applicability of the empirical magnitude–yield relations developed for northeast China and Korean Peninsula explosions was investigated for data from northwest China. We collected regional broadband digital seismic data from 13 chemical explosions (CEx) detonated between 6 September and 10 October 2018, on the eastern margin of the Junggar basin, northwest China, five nuclear tests at the Semipalatinsk nuclear test site, and eight natural earthquakes. Both Lg and Rayleigh‐wave magnitudes (⁠$mb(Lg)$ and $Ms$⁠, respectively) were estimated for these events. Similar to the North Korean test site, the $mb(Lg)–Ms$ discriminant did not properly distinguish explosions from natural earthquakes at the Semipalatinsk test site. However, network‐averaged P/S spectral ratios (Pg/Lg, Pn/Lg, and Pn/Sn) did successfully discriminate explosions from earthquakes at both the North Korean and the Semipalatinsk test sites at frequencies above 2.0 Hz. Based on 13 known‐yield CEx, we selected an empirical magnitude–yield relation to constrain the explosive yields of five historical nuclear tests at the Semipalatinsk test site. The resulting yields are lower than those previously obtained from teleseismic observations.