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

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.

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Generalized orthonormal moment tensor decomposition and its source-type diagram

Journal of Seismology ◽

10.1007/s10950-020-09951-2 ◽

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.

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Analysis of non-double-couple source mechanisms in an area of induced seismicity, West Texas (USA).

10.5194/egusphere-egu21-13438 ◽

2021 ◽

Author(s):

Savvaidis Alexandros ◽

Roselli Pamela

Keyword(s):

Stress Field ◽

Time Domain ◽

Seismic Moment ◽

Moment Tensor ◽

P Wave ◽

Seismic Moment Tensor ◽

Ground Displacement ◽

Moment Tensors ◽

West Texas ◽

Double Couple

In the scope to investigate the possible interactions between injected fluids, subsurface geology, stress field and triggering earthquakes, we investigate seismic source parameters related to the seismicity in West Texas (USA). The analysis of seismic moment tensor is an excellent tool to understand earthquake source process kinematics; moreover, changes in the fluid volume during faulting leads to existence of non-double-couple (NDC) components (Frohlich, 1994; Julian et al., 1998; Miller et al., 1998). The NDC percentage in the source constitutes the sum of absolute ISO and CLVD components so that %NDC= % ISO + %CLVD and %ISO+%CLVD+%DC=100%. It is currently known that the presence of NDC implies more complex sources (mixed shear-tensile earthquakes) correlated to fluid injections, geothermal systems and volcano-seismology where induced and triggered seismicity is observed.With this hypothesis, we analyze the micro-earthquakes (M <2 .7) recorded by the Texas Seismological Network (TexNet) and a temporary network constituted by 40 seismic stations (equipped by either broadband or 3 component geophones). Our study area is characterized by Northwest-Southeast faults that follow the local stress/field (SHmax) and the geological characteristic of the shallow basin structure of the study area. After a selection based on signal-to-noise ratio, we filter (1-50 Hz) the seismograms and estimate P-wave pulse polarities and the first P-wave ground displacement pulse in time domain. Then, we perform the full moment tensor analysis by using hybridMT technique (Andersen, 2001; Kwiatek et al., 2016) with a detailed 1D velocity model. The key parameter is the polarity/area of the first P-wave ground displacement pulse in time domain. Uncertainties of estimated moment tensors are expressed by normalized root-mean-square (RMS errors) between theoretical and estimated amplitudes (Vavricuk et al., 2014). We also evaluate the quality of the seismic moment tensors by bootstrap and resampling. In our preliminary results we obtain NDC percentage (in terms of %ISO and %CLVD components), Mw, seismic moment, P, T and B axes orientation for each source inverted.

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

10.26686/wgtn.16947268 ◽

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

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.

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A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes

Bulletin of the Seismological Society of America ◽

10.1785/bssa0730020419 ◽

1983 ◽

Vol 73 (2) ◽

pp. 419-434

Author(s):

Jeffery S. Barker ◽

Charles A. Langston

Keyword(s):

Body Wave ◽

Moment Tensor ◽

Normal Fault ◽

Strike Slip ◽

Body Waves ◽

P Wave ◽

Moment Tensors ◽

Double Couple ◽

The Moment ◽

Mammoth Lakes

abstract Teleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.

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KAMCHATKA AND COMMANDER ISLANDS

Zemletriaseniia Severnoi Evrazii [Earthquakes in Northern Eurasia] ◽

10.35540/1818-6254.2020.23.16 ◽

2020 ◽

pp. 172-182

Author(s):

D. Chebrov ◽

A. Chebrova ◽

I. Abubakirov ◽

E. Matveenko ◽

S. Mityushkina ◽

...

Keyword(s):

Moment Tensor ◽

Seismic Intensity ◽

Earthquake Catalogue ◽

Seismic Moment Tensor ◽

Magnitude Of Completeness ◽

Commander Islands ◽

Strong Earthquakes ◽

Double Couple ◽

Kamchatka Earthquake ◽

Surrounding Areas

The seismicity review of Kamchatka and surrounding territories for 2014 is given. In Kamchatka earthquake catalogue minimum local magnitude of completeness is MLmin=3.5, and for earthquakes under the Okhotsk sea with h≥350 kmMLmin=3.6. The Kamchatka earthquake catalogue for 2014 with ML3.5, published in the Appendix to this annual, includes 1114 events. 86 earthquakes of the catalogue with ML=3.35–6.2 were felt in Kamchatka and surrounding areas with seismic intensity I ranged from 2 to 5 according the MSK-64 scale. For all events with ML5.0 occurred in the area of responsibility of the KB GS RAS in 2014, an attempt to calculate the seismic moment tensor (SMT) was made. There are 40 such events in the regional catalogue. For 36 earthquakes, the SMT and depth h of the equivalent point source were calculated successfully. The calcu-lations were performed for the SMT double-couple model using a nonlinear algorithm. In 2014, a typical location of the earthquake epicenters was observed in the Kamchatka zone. In 2014, the seismicity level in all selected zones and in the region as a whole corresponded to the background one according to the “SESL’09” scale. The number of recorded events with ML3.6 and strong earthquakes with ML5.1 is close to the average annual value. Anomalous and outstanding events were not recorded.

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Moving from 1-D to 3-D velocity model: automated waveform-based earthquake moment tensor inversion in the Los Angeles region

Geophysical Journal International ◽

10.1093/gji/ggz435 ◽

2019 ◽

Vol 220 (1) ◽

pp. 218-234 ◽

Cited By ~ 4

Author(s):

Xin Wang ◽

Zhongwen Zhan

Keyword(s):

Los Angeles ◽

Moment Tensor ◽

Velocity Model ◽

Primary Control ◽

Lateral Velocity ◽

Real Time System ◽

Moment Tensors ◽

Velocity Models ◽

Double Couple ◽

The Moment

SUMMARY Earthquake focal mechanisms put primary control on the distribution of ground motion, and also bear on the stress state of the crust. Most routine focal mechanism catalogues still use 1-D velocity models in inversions, which may introduce large uncertainties in regions with strong lateral velocity heterogeneities. In this study, we develop an automated waveform-based inversion approach to determine the moment tensors of small-to-medium-sized earthquakes using 3-D velocity models. We apply our approach in the Los Angeles region to produce a new moment tensor catalogue with a completeness of ML ≥ 3.5. The inversions using the Southern California Earthquake Center Community Velocity Model (3D CVM-S4.26) significantly reduces the moment tensor uncertainties, mainly owing to the accuracy of the 3-D velocity model in predicting both the phases and the amplitudes of the observed seismograms. By comparing the full moment tensor solutions obtained using 1-D and 3-D velocity models, we show that the percentages of non-double-couple components decrease dramatically with the usage of 3-D velocity model, suggesting that large fractions of non-double-couple components from 1-D inversions are artifacts caused by unmodelled 3-D velocity structures. The new catalogue also features more accurate focal depths and moment magnitudes. Our highly accurate, efficient and automatic inversion approach can be expanded in other regions, and can be easily implemented in near real-time system.

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Seismic moment tensors from synthetic rotational and translational ground motion: Green’s functions in 1-D versus 3-D

Geophysical Journal International ◽

10.1093/gji/ggaa305 ◽

2020 ◽

Vol 223 (1) ◽

pp. 161-179

Author(s):

S Donner ◽

M Mustać ◽

B Hejrani ◽

H Tkalčić ◽

H Igel

Keyword(s):

Ground Motion ◽

Seismic Moment ◽

Structural Model ◽

Moment Tensor ◽

Waveform Inversion ◽

Seismic Moment Tensor ◽

Tectonic Event ◽

Moment Tensors ◽

Rotational Ground Motion ◽

D Model

SUMMARY Seismic moment tensors are an important tool and input variable for many studies in the geosciences. The theory behind the determination of moment tensors is well established. They are routinely and (semi-) automatically calculated on a global scale. However, on regional and local scales, there are still several difficulties hampering the reliable retrieval of the full seismic moment tensor. In an earlier study, we showed that the waveform inversion for seismic moment tensors can benefit significantly when incorporating rotational ground motion in addition to the commonly used translational ground motion. In this study, we test, what is the best processing strategy with respect to the resolvability of the seismic moment tensor components: inverting three-component data with Green’s functions (GFs) based on a 3-D structural model, six-component data with GFs based on a 1-D model, or unleashing the full force of six-component data and GFs based on a 3-D model? As a reference case, we use the inversion based on three-component data and 1-D structure, which has been the most common practice in waveform inversion for moment tensors so far. Building on the same Bayesian approach as in our previous study, we invert synthetic waveforms for two test cases from the Korean Peninsula: one is the 2013 nuclear test of the Democratic People’s Republic of Korea and the other is an Mw 5.4 tectonic event of 2016 in the Republic of Korea using waveform data recorded on stations in Korea, China and Japan. For the Korean Peninsula, a very detailed 3-D velocity model is available. We show that for the tectonic event both, the 3-D structural model and the rotational ground motion, contribute strongly to the improved resolution of the seismic moment tensor. The higher the frequencies used for inversion, the higher is the influence of rotational ground motions. This is an important effect to consider when inverting waveforms from smaller magnitude events. The explosive source benefits more from the 3-D structural model than from the rotational ground motion. Nevertheless, the rotational ground motion can help to better constraint the isotropic part of the source in the higher frequency range.

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SEISMICITY of KAMCHATKA and COMMANDER ISLANDS in 2015

Zemletriaseniia Severnoi Evrazii [Earthquakes in Northern Eurasia] ◽

10.35540/1818-6254.2021.24.14 ◽

2021 ◽

pp. 153-163

Author(s):

D. Chebrov ◽

V. Saltikov ◽

E. Matveenko ◽

S. Droznina ◽

E. Romasheva ◽

...

Keyword(s):

Moment Tensor ◽

Seismic Intensity ◽

Earthquake Catalogue ◽

Seismic Moment Tensor ◽

Commander Islands ◽

Strong Earthquakes ◽

Significant Events ◽

Double Couple ◽

Kamchatka Earthquake ◽

Surrounding Areas

The seismicity review of Kamchatka and surrounding territories for 2015 is given. In the Kamchatka earthquake catalogue, the minimum local magnitude of completeness is MLmin=3.5, and for earthquakes with h≥350 km under the Okhotsk sea MLmin=3.6. The Kamchatka earthquake catalogue for 2015 with ML3.5, published in the Appendix to this issue, includes 1213 events. 92 earthquakes of the catalogue with ML=3.0–6.5 were felt in Kamchatka and surrounding areas with seismic intensity I=2–6 according to the MSK-64 scale. For all events with ML5.0 that occurred in 2015 in the KB GS RAS area of responsibility, an attempt to calculate the seismic moment tensor (SMT) was made. There are 32 such events in the regional catalogue. For 28 earthquakes the SMT and depth h of the equivalent point source were calculated successfully. The calculations were performed for the SMT double-couple model using a nonlinear algorithm. In 2015, a typical location of the earthquake epicenters was observed in the Kamchatka zone. In 2015, the seismicity level in all selected zones and in the region as a whole correspond to the background one according to the “SESL’09” scale. The number of recorded events with ML3.5 and strong earthquakes with ML5.0 is close to the average annual value. Anomalous and significant events were not recorded.

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

Bulletin of the Seismological Society of America ◽

10.1785/0120190062 ◽

2020 ◽

Vol 110 (1) ◽

pp. 166-177 ◽

Cited By ~ 2

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.

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