This electronic supplement contains figures comparing Pn waveforms from North Korean test site (NKTS) explosions and three aftershocks recorded at YNB station and the spectral ratios from individual stations and events for six North Korean underground nuclear tests, three postexplosion seismic events, and four nearby earthquakes, as well as a table of the residuals of Pn differential travel times at individual stations.
Table S1. Pn differential travel times at individual stations. The data recorded at stations 1–726 are not available for international users outside China mainland. The provincial network codes are BJ, Beijing; TJ, Tianjin; HE, Hebei; HL, Heilongjiang; JL, Jilin; LN, Liaoning; NM, Neimeng; SD, Shandong; and SX, Shanxi Provinces. The BU network is affiliated with the Institute of Geophysics, China Earthquake Administration (CEA). IC, II, IU, JP, KG, and KS belong to the Global Seismograph Network (GSN); BO represents Japan F-net network. Δt0, measured differential travel time in milliseconds with a zero mean. Δt1, corrected differential travel time in milliseconds with the best-fitting locations of the NKT1–NKT6 and PEV1–PEV3. NKT1–NKT6, six North Korean nuclear tests occurred in 2006, 2009, 2013, January and September 2016, and 2017, respectively. PEV1–PEV3, three postexplosion events at the North Korean nuclear test site on 3 and 23 September and 12 October 2017, respectively.
Figure S1. Comparisons of Pn waveforms from NKTS explosions and three aftershocks recorded at YNB station. Event names, cross-correlation coefficients (R), and differential travel times (T) are all labeled on the traces. The inset map illustrates the locations of NKTS (solid red star) and some close-in stations, where the YNB is highlighted by green.
Figure S2. Spectral ratios from individual stations and events, where the shaded areas indicate the standard errors.
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