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.

scholarly journals Adaptive moment-tensor joint inversion of clustered microseismic events for monitoring geological carbon storage

2019 ◽  
Vol 219 (1) ◽  
pp. 80-93
Author(s):  
Yu Chen ◽  
Lianjie Huang
Keyword(s):  
Carbon Storage ◽  
Oil Recovery ◽  
Joint Inversion ◽  
Moment Tensor ◽  
Crack Opening ◽  
Cost Effective ◽  
Microseismic Monitoring ◽  
Moment Tensor Inversion ◽  
Inversion Method ◽  
Microseismic Events

SUMMARY Moment-tensor inversion of induced microseismic events can provide valuable information for tracking CO2 plumes at geological carbon storage sites, and study the physical mechanism of induced microseismicity. Accurate moment-tensor inversion requires a wide-azimuthal coverage of geophones. Cost-effective microseismic monitoring for geological carbon storage often uses only one geophone array within a borehole, leading to a large uncertainty in moment-tensor inversion. We develop a new adaptive moment-tensor joint inversion method to reduce the inversion uncertainty, when using limited but typical geophone receiver geometries. We first jointly invert a number of clustered microseismic events using a uniform focal mechanism to minimize the waveform misfit between observed and predicted P and S waveforms. We then invert the moment tensor for each event within a limited searching range around the joint inversion result. We apply our adaptive joint inversion method to microseismic data acquired using a single borehole geophone array at the CO2-Enhanced Oil Recovery field at Aneth, Utah. We demonstrate that our inversion method is capable of reducing the inversion uncertainty caused by the limited azimuthal coverage of geophones. Our inverted strikes of focal mechanisms of microseismic events are consistent with the event spatial distribution in subparallel pre-existing fractures or geological imperfections. The large values up to 40 per cent of the CLVD components might indicate crack opening induced by CO2/wastewater injection or rupture complexity.

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.

Microseismic moment-tensor inversion and sensitivity analysis in VTI media

Geophysics ◽  
2020 ◽  
pp. 1-74
Author(s):  
Han Li ◽  
Xu Chang ◽  
Xiao-Bi Xie ◽  
Yibo Wang
Keyword(s):  
Hydraulic Fracturing ◽  
Focal Mechanism ◽  
Moment Tensor ◽  
Staggered Grid ◽  
Inversion Method ◽  
Model Parameters ◽  
Seismic Moment Tensor ◽  
Tensor Model ◽  
Double Couple ◽  
The Impact

Through the study of microseismic focal mechanisms, information such as fracture orientation, event magnitude, and in-situ stress status can be quantitatively obtained, thus, providing a reliable basis for unconventional oil and gas exploration. Most source inversion methods assume that the medium is isotropic. However, hydraulic fracturing is usually conducted in sedimentary rocks, which often exhibit strong anisotropy. Neglecting this anisotropy may cause errors in focal mechanism inversion results. We propose a microseismic focal mechanism inversion method that considers velocity anisotropy in a vertically transverse isotropic (VTI) medium. To generate synthetic data, we adopt the moment-tensor model to represent microearthquake sources. We use a staggered-grid finite-difference (SGFD) method to calculate synthetic seismograms in anisotropic media. We perform seismic moment-tensor (SMT) inversion with only P-waves by matching synthetic and observed waveforms. Both synthetic and field datasets are used to test the inversion method. For the field dataset, we investigate the inversion stability using randomly selected partial datasets in the calculation. We pay special attention to analyze the sensitivity of the inversion. We test and evaluate the impact of noise in the data and errors in the model parameters ( VP0, ε, and δ) on the SMT inversion using synthetic datasets. The results indicate that for a surface acquisition system, the proposed method can tolerate moderate noise in the data, and deviations in the anisotropy parameters can cause errors in the SMT inversion, especially for dip-slip events and the inverted percentages of non-double-couple components. According to our study, including anisotropy in the model is important to obtain reliable non-double-couple components of moment tensors for hydraulic fracturing induced microearthquakes.

scholarly journals Edges of overlying seams as a factor responsible for strong mining tremors occurrence during underground hard coal extraction in the light of seismic moment tensor inversion method

2019 ◽  
Vol 133 ◽  
pp. 01005
Author(s):  
Łukasz Wojtecki ◽  
Adam Mirek ◽  
Grażyna Dzik
Keyword(s):  
Seismic Moment ◽  
Longwall Mining ◽  
Moment Tensor ◽  
Moment Tensor Inversion ◽  
Coal Extraction ◽  
Hard Coal ◽  
Inversion Method ◽  
Seismic Moment Tensor ◽  
The Difference ◽  
Mining Tremors

Physical processes occurring in the focus of tremor can be identified by solving a focal mechanism via the seismic moment tensor inversion method. In this article the estimation of focal mechanisms of strong mining tremors (according to Polish law tremors of energy higher or equal 1·105 J), which occurred during longwall mining of coal seam no. 507 in one of the hard coal mines in the Polish part of Upper Silesian Coal Basin was performed. Totally 7 strong mining tremors with the local magnitude from 1.84 to 2.52 were analysed. The most probable geomechanical processes in the foci of these tremors have been reconstructed. An attempt to determine the correlation between the edges of overlying seams no. 502, 504 or 506 and strong mining tremors occurrence has been made. The strike of determined nodal planes is in accordance with the azimuth of mentioned edges. The difference between them (absolute value) varies from 0.3° to 34.1° (on average approximately 19°).

scholarly journals Generalized orthonormal moment tensor decomposition and its source-type diagram

2020 ◽  
Author(s):  
Ting-Chung Huang ◽  
Yih-Min Wu
Keyword(s):  
Seismic Moment ◽  
Decomposition Method ◽  
Moment Tensor ◽  
Tensor Decomposition ◽  
New Method ◽  
Seismic Moment Tensor ◽  
Linear Vector ◽  
Source Type ◽  
Sign Problem ◽  
Double Couple

Abstract Moment tensor decomposition is a method for deriving the isotropic (ISO), double-couple (DC), and compensated linear vector dipole (CLVD) components from a seismic moment tensor. Currently, there are two families of methods, namely, standard moment tensor decomposition and Euclidean moment tensor decomposition. Although both methods can usually provide workable solutions, there are some minor inconsistencies between the two methods: an equality inconsistency that occurs in standard moment tensor decomposition and the pure CLVD unity and flip basis inconsistency encountered in Euclidean moment tensor decomposition. Moreover, there is a sign problem when disentangling the CLVD component from a DC-dominated case. To address these minor inconsistencies, we propose a new moment tensor decomposition method inspired by both previous methods. The new method can not only avoid all these minor inconsistencies but also withstand deviations in ISO- or CLVD-dominated cases when using source-type diagrams.

Aftershocks of the 1952 Kern County, California, earthquake sequence

1999 ◽  
Vol 89 (4) ◽  
pp. 1094-1108 ◽  
Author(s):  
Douglas Dreger ◽  
Brian Savage
Keyword(s):  
Sierra Nevada ◽  
Dynamic Range ◽  
Moment Tensor ◽  
Source Parameters ◽  
High Dynamic Range ◽  
Earthquake Sequence ◽  
Seismic Moment Tensor ◽  
Kern County ◽  
Waveform Modeling ◽  
First Motion

Abstract We have studied the seismograms recorded at the historic Berkeley (BRK) and Pasadena (PAS) stations for 20 aftershocks of the 21 July 1952 Kern County earthquake sequence. These events, in the magnitude range of MW 4.5 to 5.6, are too small to be studied teleseismically, yet they are important for better understanding the tectonics of the southern Sierra Nevada and the Tehachapi Mountains. On-scale recordings of moderate-sized events from this important earthquake sequence were first scanned, digitized, and then subjected to waveform modeling using a seismic moment tensor inverse procedure. In particular, the long-period, three-component Galitzen instrument at BRK and the 6-sec Wood-Anderson at PAS provided very high quality seismograms that could be analyzed in this manner. These two sites have been continuously operated from 1887 and 1927, respectively, and both are current sites of state-of-the-art broadband, high dynamic range instrumentation. First-motion polarities reported by Bath and Richter (1958) were used as additional constraints in the estimation of source parameters. There is considerable variability in the three-component seismograms of the 1952 aftershocks, which in turn result in a diversity of focal mechanisms. The majority of the solutions are northwest-striking reverse mechanisms that likely occurred on various mapped thrust faults in the hanging block of the mainshock. There are several events with northeast-striking, left-lateral mechanisms that are consistent with the strike of the White Wolf fault, as well as several normal slip events. The results of this study indicate that there are a variety of active fault structures adjacent to the White Wolf, Garlock and San Andreas faults in this 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

<p>Strong ground motions induced by North Korea’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.</p>

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