Modeling 0-2 Hz 3D Wave Propagation of the North Korean Nuclear Tests Across the Sea of Japan

Date: 4/24/2019

Time: 04:45 PM

Room: Cascade I

We have simulated 0-4 Hz wave propagation for the 2009 nuclear test on the Korean Peninsula in the SALSA3D velocity model developed by Sandia and LANL (Begnaud, 2015). The simulations are carried out using the highly scalable 4th-order finite-difference GPU-enabled code AWP-ODC code with discontinuous mesh capabilities. Broadband observations at regional distances (~500 km) are well modeled when appropriate statistical distributions of small-scale heterogeneities are included in the crust. We find that at INCN, the phase amplitudes and Pn/Lg, Pg/Lg and Pn/Sn ratios for data fall within the standard deviation of those calculated from the synthetic ensembles for an isotropic source at the North Korea Nuclear Test Site (NKNTS) for almost all frequencies between 0.5 and 4 Hz. This result is then used to calculate P/S ratios for isotropic and double-couple sources at all distances from NKNTS to station INCN. We carried out array analysis for KSRS data and synthetics for the 2009 event. Our results suggest that crustal small-scale heterogeneities with parameters constrained by our study are needed to reproduce the coherence from the data, and that array analysis is capable of constraining the properties of the velocity structure in this region. We find that a different scattering behavior appears to be associated with the two different source types (e.g., P-S versus S-P scattering), indicating that the predominant S wave train for the double-couple source is very efficiently generating converted S-P scattered waves after Pn. We also model broadband stations in Japan for the 2017 mb=6.3 event at NKNTS (~1200 km) to better understand the leakage of Lg energy at the transition between the continental and oceanic crustal layers, as well as the formation of the long-period Rayleigh waves widely observed at stations in Japan. We show the contributions in the synthetics from both isotropic and non-isotropic moment tensor components to address S-wave generation in the source area.

Presenting Author: Te-Yang Yeh

Authors