Generalized Source Model of the North Korea Tests 2009–2017

Abstract

The 2017 North Korea test is analyzed together with the previous 2009-2016 tests, and a generalized source model is derived using waveform data. Data are represented by lowfrequency records of 11 broadband near-regional stations (epicentral distances 140-310 km), bandpassed from 0.03 to 0.09 Hz. The events feature a significant degree of similarity. Therefore, mean records can be calculated by averaging the five tests, using the cross-correlation shifts and amplitude scaling. The mean records are inverted for the full moment tensor in terms of its posterior probability density function. The meansource model reveals significant uncertainties and parameter tradeoffs, due to well-known resolution problems at shallow depths and long wavelengths. Nevertheless, the moment tensor is undoubtedly dominated by its nonshear parts, that is, the isotropic component, and compensated linear vector dipole (inclined ∼15°to the vertical). The source type is very close to an opening crack, consistent with existing physical models of explosive shallow sources, accompanied by material damage. The generalized source model presented here is new. It can be used as a prior, realistically constrained model, applicable in early discriminations between natural earthquakes and explosions at the test site. Users at any station (not involved in this study) could precompute template synthetics in their preferred frequency ranges and velocity models. If fitting with real data by a single-constant source scaling, a real-time indication of an explosion similar to the previous Democratic People's Republic of Korea (DPRK) tests can be obtained. Electronic Supplement: Tables and figures illustrating details of the individual 2009-2017 tests and of the mean-source model. METHOD Moment Tensor Inversion and Resolution AnalysisThis issue has been thoroughly explained in Paper 1; thus we present only a short summary herein. Seismic waveforms are inverted for full MT using ISOLA software (e.g., Sokos et al.,

Yield Estimates for the Six North Korean Nuclear Tests From TeleseismicPWave Modeling and Intercorrelation ofPandPnRecordings

“…A variety of methods have been used to estimate the yields or seismic moments of the six tests, including assumed transportability of body wave, surface wave, or Lg magnitude yield scaling relations (e.g., Chun et al, ; Hartmann et al, ; Yao et al, ; Zhang & Wen, ; Zhao et al, , , , , Zhao, Xie, Wang, et al, ,Zhao, Xie, He, et al, ); modeling of surface deformation (Wang et al, ; Wei, ), regional waveforms and spectra (e.g., Murphy et al, ; Rougier et al, ; Stevens & O'Brien, ; Stroujkova, ; Wang et al, ), regional coda envelopes (e.g., Pasyanos & Myers, ), network‐averaged teleseismic P wave spectra (e.g., Murphy et al, ), and teleseismic P waveforms (e.g., Chaves et al, ; Ni et al, ); and moment tensor inversion for the total and isotropic moment of the explosions (e.g., Alvizuri & Tape, ; Barth, ; Cesca et al, ; Chiang et al, ; Ford et al, ; Ichinose et al, ; Liu, Li, Zahradnik, Sokos, Liu, et al, ,Liu, Li, Zahradník, Sokos, & Plicka, ; Vavrycuk & Kim, ; Wang et al, ; Yao et al, ). Some depth constraints are inferred from infrasound as well (Assink et al, ).…”

The 2019 MW 5.7 Changning Earthquake, Sichuan Basin, China: A Shallow Doublet With Different Faulting Styles

“…At shallow depths and relatively low frequencies, the MT resolution is limited and must be accompanied by an assessment of uncertainties and parameter trade-offs (Halló et al, 2017(Halló et al, , 2019Vackář et al, 2017). Using these new methods, validated also on nuclear tests (Liu, Li, Zahradník, Sokos, & Plicka, 2018;Liu, Li, Zahradník, Sokos, Liu, & Tian, 2018) and demonstrated in Figure 2b, we find that nodal planes are strongly nonunique. While the P-axis is very well resolved (P_azimuth 69°, P_plunge 3°), the T-axis is arbitrary in the orthogonal plane.…”

Coseismic Faulting Complexity of the 2019 Mw 5.7 Silivri Earthquake in the Central Marmara Seismic Gap, Offshore Istanbul

“…To elucidate the details of the source process for the Silivri Mw5.7 mainshock, we perform a centroid-moment-tensor inversion with a special focus on the reliability of non-DC components. We use the established ISOLA software package (Zahradník and Sokos, 2018) that was recently complemented by uncertainty analyses and validated on non-shear components of nuclear tests (Liu et al, 2018a;2018b). The seismic moment tensor (MT) is solved by the least-squares method, while the centroid position is gridsearched.…”