Large Isotropic Component in the Source Mechanism of the 2013 Democratic People’s Republic of Korea Nuclear Test Revealed via a Hierarchical Bayesian Inversion

Abstract

The 12 February 2013 nuclear test conducted by the Democratic People’s Republic of Korea stands out among other nuclear tests because it produced unusually large transversal motions. Previous studies found various percentages of isotropic components of the seismic moment tensor (MT), which opens up an important question about the reliability of the methods and assumptions we routinely use to recover the seismic MT in the point source approximation. Of particular interest is the data noise model that can be utilized to represent the uncertainty associated with the recorded data. If the noise is not accounted for, this may result in a range of unwanted effects such as overfitting waveform data, and, in turn, it may lead to erroneous conclusions. We thus scrutinize the analyses of the seismic MT of this explosion by performing a thorough analysis of the source depth and time utilizing newly developed Earth structure models to invert seismograms at regional distances at different frequency bands. In addition, we estimate the solution uncertainty within a hierarchical Bayesian framework that allows accounting for noise in the data. Our results show that the resulting MT of this event contains an expectedly large isotropic component (about 70%) and a dip-slip faulting.

Resolvability of the Centroid‐Moment‐Tensors for Shallow Seismic Sources and Improvements From Modeling High‐Frequency Waveforms

“…Such a combination of subevents could be associated with the collapse of magma chamber followed by a ring-type rupture along the walls of the caldera (Fichtner & Tkalčić, 2010;Tkalčić et al, 2009). Similar scenario could be associated with nuclear explosions, where a volumetric explosion may trigger slip on nearby faults (e.g., Mustać et al, 2020). Although the estimation of CLVD and its interpretation are quite challenging, it has been associated with interesting phenomena, such as volcanic activities, fluid motions, tensile cracks, and fault complexity (see recent examples in Fontaine et al, 2019;Liu & Zahradník, 2020;White et al, 2019).…”

“…A common practice in regional CMT inversion is to derive a 1‐D local Earth model from existing information, and sometimes multiple 1‐D models for each source‐receiver paths are preferred (e.g., Mustać et al, 2020). To test a similar approach, we performed CMT inversion using a 1‐D velocity model derived from the 3‐D AusREM model beneath the source region of the earthquake.…”

“…There is an ongoing effort to address the uncertainty of the source parameters in global‐scale catalogs using data at frequencies <0.025 Hz (Stähler & Sigloch, 2014, 2016; Valentine & Trampert, 2012) as well as in regional studies—with specific applications—at frequencies >0.025 Hz (Fichtner & Simutė, 2018; Ford et al, 2010; Halló & Gallovič, 2016; Mustać et al, 2020; Mustać & Tkalčić, 2016; Scognamiglio et al, 2016; Silwal & Tape, 2016; Sokos & Zahradník, 2013; Vackář et al, 2017; Zahradník & Custódio, 2012). Estimating uncertainty of finite fault inversion of large earthquakes is gaining attention as well (Benavente et al, 2019; Dettmer et al, 2014).…”

Rotational Ground Motion Measurements for Regional Seismic Moment Tensors: a Review

“…Since a couple of years, the progress in computational and storage resources allowed to investigate the usage of 3-dimensional (3D) structural models for various studies, including regional waveform inversion for moment tensors (e. g. Hingee et al, 2011;Zhou et al, 2016;Hejrani et al, 2017). Several authors have shown that the usage of 3D structural models can be strongly beneficial for the reliability of the inversion result, that means the seismic moment tensor (e. g. Fichtner and Tkalčić, 2010;Kim et al, 2011;Covellone and Savage, 2012;Kühn and Vavryčuk, 2013;Hejrani and Tkalčić, 2020). It allows to extend the waveform inversion to higher frequency ranges, but still below the corner frequency, because the chances to decipher the more complex waveforms due to more detailed structure increase.…”

“…The determination on a regional (or even local) scale is more complicated. The stability of the waveform inversion result is affected by less well-known structural models (e. g. Šilený, 2004;Vasyura-Bathke et al, 2021), influence of theoretical and measurement noise (e. g. Sipkin, 1986;Duputel et al, 2012;Mustać et al, 2020), unfavourable event-receiver geometries (e. g. Dreger and Helmberger, 1993;Delouis and Legrand, 1999), ignored source complexities (e. g. Adamova andŠilený, 2010), and limitations of methodological approaches (e. g. Fan and Wallace, 1991;Frohlich, 1994;Julian et al, 1998;Cesca and Heimann, 2018).…”