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

2020 ◽  
Vol 110 (1) ◽  
pp. 166-177 ◽  
Author(s):  
Marija Mustać ◽  
Babak Hejrani ◽  
Hrvoje Tkalčić ◽  
Seongryong Kim ◽  
Sang-Jun Lee ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Nuclear Test ◽  
Republic Of Korea ◽  
Noise Model ◽  
Seismic Moment Tensor ◽  
Hierarchical Bayesian ◽  
Waveform Data ◽  
Isotropic Component ◽  
Recorded Data ◽  
Nuclear Tests

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.

Seismic Moment Tensor Inversion of an Induced Microseismic Event, Offshore Norway: An Insight into the Possible Cause of Wellbore Liner Failure during a Drilling Operation

2021 ◽  
Vol 92 (6) ◽  
pp. 3460-3470
Author(s):  
Zoya Zarifi ◽  
Fredrik Hansteen ◽  
Florian Schopper
Keyword(s):  
Seismic Moment ◽  
Moment Tensor ◽  
Moment Tensor Inversion ◽  
Seismic Moment Tensor ◽  
Isotropic Component ◽  
High Pump ◽  
Dc Component ◽  
Pump Pressure ◽  
Microseismic Event ◽  
Possible Cause

Abstract A microseismic event with Mw∼0.8 was recorded at the Grane oilfield, offshore Norway, in June 2015. This event is believed to be associated with a failure of the wellbore liner in well 25/11-G-8 A. The failure mechanism has been difficult to explain from drilling parameters and operational logs alone. In this study, we analyzed the detected microseismic event to shed light on the possible cause of this event. We inverted for the seismic moment tensor, analyzed the S/P amplitude ratio and radiation pattern of seismic waves, and then correlated the microseismic data with the drilling reports. The inverted seismic moment indicates a shear-tensile (dislocation) event with a strong positive isotropic component (67% of total energy) accompanied by a positive compensated linear vector dipole (CLVD) and a reverse double-couple (DC) component. Drilling logs show a strong correlation between high pump pressure and the occurrence of several microseismic events during the drilling of the well. The strongest microseismic event (Mw∼0.8) occurred during peak pump pressure of 277 bar. The application of high pump pressure was associated with an attempt to release the liner hanger running tool (RT) in the well, which had been obstructed. Improper setting of the liner hanger could have caused the forces from the RT release to be transferred to the liner and might have resulted in ripping and parting of the pipe. The possible direct impact of the ripped liner with the formation or the likely sudden hydraulic pressure exposure to the formation caused by the liner ripping may explain the estimated isotropic component in the moment tensor inversion in the well. This impact can promote slip along the pre-existing fractures (the DC component). The presence of gas in the formation or the funneled fluid to the formation caused by the liner ripping may explain the CLVD component.

scholarly journals Seismic Moment Tensor Solutions from GeoNet Data to Provide a Moment Magnitude Scale for New Zealand

2021 ◽  
Author(s):  
◽  
Elizabeth de Joux Robertson
Keyword(s):  
New Zealand ◽  
Seismic Moment ◽  
Moment Tensor ◽  
Velocity Model ◽  
Moment Tensor Inversion ◽  
Moment Magnitude ◽  
Seismic Moment Tensor ◽  
Waveform Data ◽  
Moment Tensors ◽  
The Moment

<p>The aim of this project is to enable accurate earthquake magnitudes (moment magnitude, MW) to be calculated routinely and in near real-time for New Zealand earthquakes. This would be done by inversion of waveform data to obtain seismic moment tensors. Seismic moment tensors also provide information on fault-type. I use a well-established seismic moment tensor inversion method, the Time-Domain [seismic] Moment Tensor Inversion algorithm (TDMT_INVC) and apply it to GeoNet broadband waveform data to generate moment tensor solutions for New Zealand earthquakes. Some modifications to this software were made. A velocity model can now be automatically used to calculate Green's functions without having a pseudolayer boundary at the source depth. Green's functions can be calculated for multiple depths in a single step, and data are detrended and a suitable data window is selected. The seismic moment tensor solution that has either the maximum variance reduction or the maximum double-couple component is automatically selected for each depth. Seismic moment tensors were calculated for 24 New Zealand earthquakes from 2000 to 2005. The Global CMT project has calculated CMT solutions for 22 of these, and the Global CMT project solutions are compared to the solutions obtained in this project to test the accuracy of the solutions obtained using the TDMT_INVC code. The moment magnitude values are close to the Global CMT values for all earthquakes. The focal mechanisms could only be determined for a few of the earthquakes studied. The value of the moment magnitude appears to be less sensitive to the velocity model and earthquake location (epicentre and depth) than the focal mechanism. Distinguishing legitimate seismic signal from background seismic noise is likely to be the biggest problem in routine inversions.</p>

Focal mechanisms of the 2017 North Korean nuclear test and its early collapse event

2019 ◽  
Vol 220 (2) ◽  
pp. 737-752 ◽  
Author(s):  
Henglei Xu ◽  
Sidao Ni ◽  
Wenxue Liu ◽  
Haofeng Zhu ◽  
Xuliang Wang
Keyword(s):  
Surface Wave ◽  
Wave Amplitude ◽  
Amplitude Ratio ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Focal Mechanisms ◽  
Nuclear Test ◽  
Quality Data ◽  
Waveform Data ◽  
Event Identification

SUMMARY North Korea conducted sixth underground nuclear test on 3 September 2017. Unlike its previous tests, a rare subsequent collapse event occurred after about 8.5 min. As two types of distinctive shallow seismic events, accurate inversion of their focal mechanisms is important for event identification for CTBT. In this paper, we carry out moment tensor inversion of the nuclear test and the collapse event with gCAP using waveform data from dense regional seismic stations. And their focal mechanisms are further constrained with surface wave amplitude ratio. The results show that the surface wave amplitude ratio has further constraints for screening the waveform inversion results. The resolution of the focal mechanism inversion for the nuclear test is high, which is close to a Crack source. However, the resolution for the collapse event inversion is not so high and the source type is difficult to be accurately determined. One reason of the poor resolution for the collapse event may be due to the limited availability of high quality data, and complexity of the source process might be another factor.

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

2021 ◽  
Vol 1 (2) ◽  
pp. 107-116
Author(s):  
Rodrigo Chi-Durán ◽  
Douglas S. Dreger ◽  
Arthur J. Rodgers ◽  
Avinash Nayak
Keyword(s):  
Ground Deformation ◽  
Joint Inversion ◽  
Moment Tensor ◽  
Permanent Deformation ◽  
Nuclear Test ◽  
Inversion Method ◽  
Seismic Moment Tensor ◽  
Source Type ◽  
Best Fitting ◽  
First Motion

Abstract The 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.

Path Calibration of the Democratic People’s Republic of Korea 3 September 2017 Nuclear Test

2021 ◽  
Author(s):  
Douglas S. Dreger ◽  
Roland Gritto ◽  
Owen Nelson
Keyword(s):  
Moment Tensor ◽  
Source Parameters ◽  
Seismic Source ◽  
Nuclear Test ◽  
Republic Of Korea ◽  
Source Analysis ◽  
The Sea Of Japan ◽  
Source Modeling ◽  
Velocity Models ◽  
Cross Correlation Analysis

Abstract The recovery of seismic source parameters requires the use of calibrated velocity models. Although at long periods it is possible to use relatively simple plane-layered models, calibration is still needed to better constrain source parameters. For the Democratic People’s Republic of Korea (DPRK) nuclear tests, this is particularly true when considering the use of seismic stations in Japan where paths cross the Sea of Japan. In this study, we perform forward waveform modeling to calibrate velocity structures. We show that we can arrive at a set of models that minimizes Rayleigh group-velocity anomaly at stations located in China, South Korea, and Japan. Overall moment tensor capability with the new models is improved such that cross-correlation analysis of the 20–50 s period waveforms recovers the true time alignment of the data, enabling better automated source analysis. We performed source-type inversions for the moment tensor jointly for long-period regional waveforms and regional and teleseismic P-waves polarity data for the latest and largest DPRK nuclear test and examine event discrimination/screening capability, scalar moment, and yield estimates with uncertainty. We present the models for improved seismic source modeling of the region.

Infrasound from the North Korea underground explosion and subsequent collapse on 3 September 2017

2020 ◽  
Author(s):  
Il-Young Che ◽  
Keehoon Kim ◽  
Alexis Le Pichon
Keyword(s):  
Acoustic Waves ◽  
North Korea ◽  
Ground Motions ◽  
Moment Tensor ◽  
Nuclear Test ◽  
Acoustic Energy ◽  
Underground Explosion ◽  
Seismic Moment Tensor ◽  
Cavity Collapse ◽  
Mountainous Regions

&lt;p&gt;Strong ground motions induced by North Korea&amp;#8217;s declared underground nuclear test in September 2017 and a subsequent subsurface collapse excited substantial and characteristic atmospheric acoustic waves (infrasound) that were detected by multiple stations at regional distances. Back-projection method is applied to the detected long-lasting coherent infrasound wavetrains related to the nuclear test. This allows to reconstruct source locations and reveals ground-to-air coupling in a large area over the northeast Korean Peninsula. To understand the excitation of atmospheric acoustic phases from the underground sources, full 3-D seismo-acoustic simulations are performed with pre-defined seismic moment tensor solutions of the underground sources. The simulations quantitatively predict the excitation of epicentral and diffracted acoustic phases developed by direct vertical ground motion at the immediate epicenter and by seismic surface waves propagating through high mountainous regions, respectively. In the atmosphere, the direct acoustic phases propagate spherically at the speed of sound, but the diffracted phases form inclined wavefronts in the atmosphere as the surface wave moves away from the epicenter. On a broad scale, the simulated acoustic coupling shows good agreement with the infrasound radiation patterns determined from the infrasound observations. Additional simulations for the subsequent subsurface collapse event show that an underground cavity collapse can be a potential mechanism for the production of low-frequency acoustic energy that is also detectable at regional distances. Finally, this study highlights the link between ground motions caused by underground sources and infrasound detection, further enabling infrasound as a depth discriminant for subsurface sources.&lt;/p&gt;

scholarly journals Parametrization of general seismic potency and moment tensors for source inversion of seismic waveform data

2013 ◽  
Vol 194 (2) ◽  
pp. 839-843 ◽  
Author(s):  
Lupei Zhu ◽  
Yehuda Ben-Zion
Keyword(s):  
Moment Tensor ◽  
Relative Size ◽  
Seismic Moment Tensor ◽  
Source Inversion ◽  
Waveform Data ◽  
Moment Tensors ◽  
Linear Vector ◽  
Seismic Waveform ◽  
Isotropic Media ◽  
Double Couple

Abstract We decompose a general seismic potency tensor into isotropic tensor, double-couple tensor and compensated linear vector dipole using the eigenvectors and eigenvalues of the full tensor. Two dimensionless parameters are used to quantify the size of the isotropic and compensated linear vector dipole components. The parameters have well-defined finite ranges and are suited for non-linear inversions of source tensors from seismic waveform data. The decomposition and parametrization for the potency tensor are used to obtain corresponding results for a general seismic moment tensor. The relations between different parameters of the potency and moment tensors in isotropic media are derived. We also discuss appropriate specification of the relative size of different source components in inversions of seismic data.

scholarly journals Seismic Moment Tensor Solutions from GeoNet Data to Provide a Moment Magnitude Scale for New Zealand

2021 ◽  
Author(s):  
◽  
Elizabeth de Joux Robertson
Keyword(s):  
New Zealand ◽  
Seismic Moment ◽  
Moment Tensor ◽  
Velocity Model ◽  
Moment Tensor Inversion ◽  
Moment Magnitude ◽  
Seismic Moment Tensor ◽  
Waveform Data ◽  
Moment Tensors ◽  
The Moment

<p>The aim of this project is to enable accurate earthquake magnitudes (moment magnitude, MW) to be calculated routinely and in near real-time for New Zealand earthquakes. This would be done by inversion of waveform data to obtain seismic moment tensors. Seismic moment tensors also provide information on fault-type. I use a well-established seismic moment tensor inversion method, the Time-Domain [seismic] Moment Tensor Inversion algorithm (TDMT_INVC) and apply it to GeoNet broadband waveform data to generate moment tensor solutions for New Zealand earthquakes. Some modifications to this software were made. A velocity model can now be automatically used to calculate Green's functions without having a pseudolayer boundary at the source depth. Green's functions can be calculated for multiple depths in a single step, and data are detrended and a suitable data window is selected. The seismic moment tensor solution that has either the maximum variance reduction or the maximum double-couple component is automatically selected for each depth. Seismic moment tensors were calculated for 24 New Zealand earthquakes from 2000 to 2005. The Global CMT project has calculated CMT solutions for 22 of these, and the Global CMT project solutions are compared to the solutions obtained in this project to test the accuracy of the solutions obtained using the TDMT_INVC code. The moment magnitude values are close to the Global CMT values for all earthquakes. The focal mechanisms could only be determined for a few of the earthquakes studied. The value of the moment magnitude appears to be less sensitive to the velocity model and earthquake location (epicentre and depth) than the focal mechanism. Distinguishing legitimate seismic signal from background seismic noise is likely to be the biggest problem in routine inversions.</p>

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