Joint Regional Waveform, First-Motion Polarity, and Surface Displacement Moment Tensor Inversion of the 3 September 2017 North Korean Nuclear Test

Rodrigo Chi-Durán,Douglas S Dreger,Arthur J Rodgers,Avinash Nayak

doi:10.1785/0320210022

Abstract

AbstractThe 3 September 2017 Mw 5.2 North Korean underground nuclear test (DPRK2017) is the largest man-made explosion with surface displacements observed by Synthetic Aperture Radar (SAR) and showed as much as 3.5 m of horizontal permanent deformation. Although regional distance waveform-based seismic moment tensor (MT) inversion methods successfully identify this event as an explosion, the inverted solutions do not fit the SAR displacement field well. To better constrain the source, we developed an MT source-type inversion method that incorporates surface ground deformation (accounting for free-surface topography), regional seismic waveforms, and first-motion polarities. We applied the source-type inversion over a grid of possible source locations to find the best-fitting location, depth, and point-source MT for the event. Our best-fitting MT solution achieves ∼70% horizontal geodetic fit, ∼80% waveform fit, and 100% fit in the first-motion polarities. The joint inversion narrows the range of acceptable source types improving discrimination, and reduces the uncertainty in scalar moment and estimated yield. The method is transportable and can be applied to other types of events that may have measurable geodetic signals such as underground mine collapses and volcanic events.

Highlights

On 3 September 2017, the Democratic People’s Republic of Korea conducted its largest nuclear test (DPRK2017) at the Pungee-Ryi test site having an mb 6.3 (U.S Geological Survey [USGS] and National Earthquake Information Center) and a scalar moment of 8:06 × 1016 N · m corresponding to Mw 5.2 (Chiang et al, 2018)
This event had a substantially larger yield than previous tests and provides a high-quality seismic waveform dataset from the Chinese Digital Seismic Network (BJT, HIA, and MDJ), Korean Seismic Network (TJN), and Incorporated Research Institutions for Seismology (IRIS)-USGS Global
We report in panels (c,d) the Bowers and Hudson (1999) moment, which is defined as the sum of the isotropic moment and the maximum deviatoric eigenvalue, and as they showed it is a better estimate for non-double-couple (DC) sources such as compensated linear vector dipole (CLVD) and cracks as well as combinations of those fundamental types

Summary

Introduction

On 3 September 2017, the Democratic People’s Republic of Korea conducted its largest nuclear test (DPRK2017) at the Pungee-Ryi test site having an mb 6.3 (U.S Geological Survey [USGS] and National Earthquake Information Center) and a scalar moment of 8:06 × 1016 N · m corresponding to Mw 5.2 (Chiang et al, 2018). This event had a substantially larger yield than previous tests and provides a high-quality seismic waveform dataset from the Chinese Digital Seismic Network (BJT, HIA, and MDJ), Korean Seismic Network (TJN), and Incorporated Research Institutions for Seismology (IRIS)-USGS Global. Seismographic Network (GSN; INCN and MAJO) stations. These data have been utilized in studies of DPRK2017 and previous explosions at the test site (e.g., Ford et al, 2009, 2012; Alvizuri and Tape, 2018; Chiang et al, 2018). Above-shot ground displacement obtained from pixel tracking of Synthetic Aperture Radar (SAR) data from the German TerraSAR-X satellite (Wang et al, 2018; Fig. 1b) reveals as much as

Methods

Results

Discussion

Conclusion