Magnitude Calculation, Yield Estimation and Seismic Discrimination in Northwest China and East Kazakhstan

We investigate characteristics of regional seismic waves generated by explosion sources and recorded in Northwest China and East Kazakhstan. The sources include 13 chemical explosions with known yields, originally detonated in Northwest China for deep sounding purpose and 5 underground nuclear tests at the Soviet Semipalatinsk test site. For comparison, 8 earthquakes, of which 6 occurred in Northwest China and 2 occurred near the Semipalatinsk test site, are also included. The dataset includes 815 vertical-component broadband digital seismograms recorded at 122 stations. Based on this dataset, we exam various empirical relations previously developed in Northeast China for monitoring North Korea nuclear tests, e.g., the magnitude measurement, yield estimation and event discrimination, and evaluate their applicability in Northwest China. The global body wave magnitude m_b(P), regional body wave magnitude m_b(Lg), and Rayleigh-wave magnitude M_s are obtained for all events. Based on 13 chemical explosions with known yields, the empirical magnitude-yield relation given by Bowers et al. (2001) and adopted by Zhao et al. (2008; 2012) for North Korean nuclear test site is reevaluated and found it is likely applicable in Northwest China for Semipalatinsk nuclear tests. Comparison between m_b(P) and m_b(Lg) calculated in Northwest China reveals that the empirical relation obtained from small earthquakes may underestimate the size of large explosions. Similar to that observed at North Korean nuclear test site, the m_b(Lg) versus M_s discriminant cannot properly separate Semipalatinsk explosions from earthquakes. However, the P/S type spectral ratios, e.g., Pg/Lg, Pn/Lg and Pn/Sn, calculated in a regional network work successfully as discriminants to separate nuclear explosions from earthquakes in Northwest China. This research was supported by the National Key Research and Development Program of China (2017YFC0601206) and the National Natural Science Foundation of China (41630210, 41674060).