Numerical Simulation of Topographic and Crustal Scattering – Case Study of the 2009 DPRK Nuclear Explosion

Session: Numerical Modeling of Rupture Dynamics, Earthquake Ground Motion and Seismic Noise
Type: Oral
Date: 4/29/2020
Time: 09:30 AM
Room: 230 + 235
Description: 

We estimate the relative contribution from 0-4 Hz topographic and crustal scattering at regional distances on the Korean Peninsula from shallow DPRK nuclear explosions using 3D finite-difference simulations. The simulations are carried out in a curvilinear coordinate system to accommodate non-planar topography field, following O’Reilly et al. (2019). Olsen et al. (2018) showed using simulation with isotropic sources in the SALSA3D model that crustal small-scale heterogeneities were needed to adequately model the observed strong scattering effects at distances of 400 - 500 km from the 2009 DPRK nuclear explosion. Here, we quantify the additional scattering generated by mountain topography and the effects of the ocean water layer, which were omitted in Olsen et al. (2018). Our simulations use the inverted moment tensor source obtained by Chiang et al. (2018), which provides an improved fit to the long-period S-waves, as compared to isotropic sources. Our results show that the topography of the Korean Peninsula generates considerable amount of scattering for the 2009 DPRK nuclear test at regional distances, which greatly reduces the amplitudes of the high-frequency Rayleigh waves and enhance the P-wave coda. On the other hand, our simulations show that small-scale heterogeneities in the shallow crust are still required to reduce the amplitudes of Pn and high-frequency Lg waves to the observed range. The ocean water layer further reduces the Rayleigh wave amplitudes, to the level observed in regional records. Our results thus warrant additional simulations to determine a revised set of statistical parameters that characterizes the crustal small-scale heterogeneities, while considering topography and water.

Presenting Author: Te-Yang Yeh

Authors