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B. H. Jacobsen

Constraints of crustal heterogeneity and Q(f) from regional (< 4 Hz) wave propagation for the 2009 North Korea nuclear test

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  • Kim B. Olsen, San Diego State University
  • ,
  • Michael Begnaud, Los Alamos National Laboratory
  • ,
  • Scott Phillips, Los Alamos National Laboratory
  • ,
  • Bo Holm Jacobsen

We carried out 3D finite-difference (FD) simulations (< 4 Hz) of regional wave propagation for the 2009 North Korea nuclear explosion and compared the synthetics with instrument-corrected records at stations INCN and TJN in South Korea. The source is an isotropic explosion with a moment magnitude of 4.1. Synthetics computed in the relatively smooth Sandia/Los Alamos National Laboratory SALSA3D (SAndia LoS Alamos 3D) velocity model significantly overpredict Rayleigh-wave amplitudes by more than an order of magnitude while underpredicting coda amplitudes. The addition to SALSA3D of a von Karman distribution of small-scale heterogeneities with correlation lengths of ∼1000 m, a Hurst number of 0.1, and a horizontal-to-vertical anisotropy of ∼5 produces synthetics in general agreement with the data. The best fits are obtained from models with a gradient in the strength of the velocity and density perturbations and strong scattering (10%) limited to the top 7.5–10 km of the crust. Deeper scattering tends to decrease the initial P-wave amplitudes to levels much below those for the data, a critical result for methods discriminating between explosive and earthquake sources. In particular, the amplitude at the onset of Pn can be affected by as little as 2% small-scale heterogeneity in the lower crust and upper mantle. Simulations including a constant Q of 200 (INCN) to 350 (TJN) below 1 Hz and a power-law Q(f) formulation at higher frequencies, with an exponent of 0.3, generate synthetics in best agreement with the data. In our simulations, very limited scattering contribution from the near-source area accumulates along the regional path.

Original languageEnglish
JournalBulletin of the Seismological Society of America
Pages (from-to)1369-1383
Number of pages15
Publication statusPublished - 1 Jun 2018

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