scholarly journals Moment tensor catalogue of microearthquakes in West Bohemia from 2008 to 2018

2021 ◽  
Author(s):  
Václav Vavryčuk ◽  
Petra Adamová ◽  
Jana Doubravová ◽  
Josef Horálek
Keyword(s):  
Seismic Anisotropy ◽  
Moment Tensor ◽  
Technical Specification ◽  
Local Stress ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Moment Tensors ◽  
West Bohemia ◽  
Double Couple ◽  
Tensile Fracturing

Abstract. We present a unique catalogue of full moment tensors (MTs) of microearthquakes that occurred in West Bohemia, Czech Republic, in the period from 2008 to 2018. The catalogue is exceptional in several aspects: (1) it represents an extraordinary extensive dataset of more than 5.000 MTs, (2) it covers a long period of seismicity in the studied area, during which several prominent earthquake swarms took place, (3) the locations and retrieved MTs of microearthquakes are of a high accuracy. Additionally, we provide three-component records at the West Bohemia (WEBNET) seismic stations, the velocity model in the region, and the technical specification of the stations. The dataset is ideal for being utilized by a large community of researchers for various seismological purposes, e.g., for studies of (1) the migration of foci and the spatiotemporal evolution of seismicity, (2) redistribution of stress during periods of intense seismicity, (3) the interaction of faults, (4) the Coulomb stress along the faults and local stress anomalies connected to fault irregularities, (5) diffusivity of fluids along the activated faults, or (6) the time-dependent seismic risk due to the migration of seismicity in the region. In addition, the dataset is optimum for developing and testing new inversions for MTs and for tectonic stress. Since most of the earthquakes are non-shear, the dataset can contribute to studies of non-double-couple components of MTs and their relation to shear-tensile fracturing and/or seismic anisotropy in the focal zone.

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

2019 ◽  
Vol 220 (1) ◽  
pp. 218-234 ◽  
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.

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

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.

Focal Mechanisms of West Bohemia, Central Europe, Earthquakes—End of May 2014: Evidence of Volume Changes

2021 ◽  
Author(s):  
Dana Křížová ◽  
Jiří Málek
Keyword(s):  
Central Europe ◽  
Moment Tensor ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Earthquake Swarms ◽  
Quaternary Volcanism ◽  
Moment Tensors ◽  
Isotropic Part ◽  
West Bohemia ◽  
Source Mechanisms

Abstract West Bohemia is a region with a lot of mineral springs and gas outflows, which seems to be related to the remains of Quaternary volcanism in Central Europe. Earthquake swarms in shallow depths (less than 15 km) are very frequent there. We focused on the strongest earthquake over the past 30 yr (31 May, 2014 Mw∼3.8) and on two smaller ones (Mw∼2.9 and 2.5) from the same day. Seismograms from local and regional seismic stations were used to calculate the full and deviatoric moment tensors using low-frequency full-waveform inversion. The studied events have similar source mechanisms. The aforementioned earthquake sequence was selected to observe the isotropic part (negative value = implosion) of full moment tensors. It could relate to the motion and phase transition of fluids, especially water, and CO2. The main goal of this study is to contribute to clarification of the nature of earthquake swarms in the western edge of the Bohemian Massif. Negative value of the isotropic part of full moment tensor could be related to the closing of cracks and fissures during a rupture process.

Non‐Double‐Couple Moment Tensors of Earthquakes Calculated Using Empirical Green’s Functions

2019 ◽  
Vol 91 (1) ◽  
pp. 390-398
Author(s):  
Václav Vavryčuk ◽  
Petra Adamová
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Joint Inversion ◽  
Velocity Model ◽  
Moment Tensors ◽  
Empirical Green’S Functions ◽  
Fracturing Process ◽  
Double Couple ◽  
Focal Zone ◽  
Empirical Green's Functions

Abstract We present a joint inversion for empirical Green’s functions (EGFs) and high‐resolution non‐double‐couple (non‐DC) moment tensors. First, the EGFs are constructed using known moment tensors of earthquakes occurring in a small focal zone. Second, the estimated EGFs are applied to refine the original moment tensors used for constructing the EGFs. Because the EGFs describe the velocity model better than the standard GFs, the refined moment tensors are more accurate. The method is applied to real observations of earthquakes of the 2008 swarm in West Bohemia, Czech Republic, where tiny details in fracturing in the focal zone are revealed. Refined moment tensors indicate fault closing caused by compaction of fault gouge during fracturing process related to fault weakening by fluids in the focal zone. The application of the proposed inversion can improve moment tensors reported in existing local, regional, or global catalogs for areas with a concentrated seismicity.

Aftershock Analysis of the 2018 Mw 7.1 Anchorage, Alaska, Earthquake: Relocations and Regional Moment Tensors

2019 ◽  
Vol 91 (1) ◽  
pp. 114-125 ◽  
Author(s):  
Natalia A. Ruppert ◽  
Avinash Nayak ◽  
Clifford Thurber ◽  
Cole Richards
Keyword(s):  
Moment Tensor ◽  
Hanging Wall ◽  
Velocity Model ◽  
Aftershock Sequence ◽  
Fault Rupture ◽  
Moment Tensors ◽  
3D Velocity Model ◽  
The Moment ◽  
The Relationship ◽  
Alaska Earthquake

Abstract The 30 November 2018 magnitude 7.1 Anchorage earthquake occurred as a result of normal faulting within the lithosphere of subducted Yakutat slab. It was followed by a vigorous aftershock sequence with over 10,000 aftershocks reported through the end of July 2019. The Alaska Earthquake Center produced a reviewed aftershock catalog with a magnitude of completeness of 1.3. This well‐recorded dataset provides a rare opportunity to study the relationship between the aftershocks and fault rupture of a major intraslab event. We use tomoDD algorithm to relocate 2038 M≥2 aftershocks with a regional 3D velocity model. The relocated aftershocks extend over a 20 km long zone between 47 and 57 km depth and are primarily confined to a high VP/VS region. Aftershocks form two clusters, a diffuse southern cluster and a steeply west‐dipping northern cluster with a gap in between where maximum slip has been inferred. We compute moment tensors for the Mw>4 aftershocks using a cut‐and‐paste method and careful selection of regional broadband stations. The moment tensor solutions do not exhibit significant variability or systematic differences between the northern and southern clusters and, on average, agree well with the mainshock fault‐plane parameters. We propose that the mainshock rupture initiated in the Yakutat lower crust or uppermost mantle and propagated both upward into the crust to near its top and downward into the mantle. The majority of the aftershocks are confined to the seismically active Yakutat crust and located both on and in the hanging wall of the mainshock fault rupture.

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>

scholarly journals Supplemental Material: Is the Eastern Denali fault still active?

2021 ◽  
Author(s):  
Minhee Choi ◽  
David W. Eaton ◽  
et al.
Keyword(s):  
Hierarchical Clustering ◽  
Moment Tensor ◽  
Velocity Model ◽  
Coulomb Stress ◽  
Stress Inversion ◽  
Moment Tensors ◽  
Stress Calculation ◽  
Denali Fault

Catalog of relocated seismicity, table of moment tensor parameters, detailed methodology of the velocity model, hierarchical clustering, moment tensors, stress inversion, Coulomb stress calculation, and Figures S1–S12.<br>

Seismic Source Processes of 25 Earthquakes (Mw>5) in the Gulf of California

2022 ◽  
Author(s):  
Eduardo Huesca-Pérez ◽  
Edahí Gutierrez-Reyes ◽  
Luis Quintanar
Keyword(s):  
Gulf Of California ◽  
Moment Tensor ◽  
Source Parameters ◽  
Seismic Source ◽  
Focal Mechanisms ◽  
Process Models ◽  
Moment Tensors ◽  
Time Space ◽  
Double Couple ◽  
Broadband Seismograms

ABSTRACT The Gulf of California (GoC) is a complex tectonic boundary that has been instrumented in the past several decades to record broadband seismograms. This volume of data has allowed us to study several source parameters systematically. Before, only a few source parameters of earthquakes greater than magnitude five had been studied in the GoC area. We re-examined the focal mechanisms of several earthquakes in the southern GoC that occurred over the last 20 yr using local–regional distance broadband seismograms. These focal mechanisms were then used as input data to retrieve the time–space history of the rupture for each earthquake. This work contributes to the study of 25 rupture-process models computed with the method proposed by Yagi et al. (1999). To investigate more about the nature of the seismicity in the GoC, we also calculated the non-double-couple component of moment tensors for 45 earthquakes. Previous studies (e.g., Ortega et al., 2013, 2016) have shown that non-double-couple components from moment tensors in this region are associated with complex faulting, suggesting that oblique faults or several parallel faults are interacting simultaneously. Our results show that, at least for moderate earthquakes (5 &lt; M &lt; 6), rupture processes in the GoC show a complex interaction between fault systems. It is revealed on the important contribution of non-double-couple component obtained in the full moment tensor analysis.

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

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;With this hypothesis, we analyze the micro-earthquakes (M &lt;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 (SH&lt;sub&gt;max&lt;/sub&gt;) 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.&lt;/p&gt;

Probabilistic Moment Tensor Inversion for Hydrocarbon-Induced Seismicity in the Groningen Gas Field, The Netherlands, Part 1: Testing

2020 ◽  
Vol 110 (5) ◽  
pp. 2095-2111 ◽  
Author(s):  
Daniela Kühn ◽  
Sebastian Heimann ◽  
Marius P. Isken ◽  
Elmer Ruigrok ◽  
Bernard Dost
Keyword(s):  
Input Data ◽  
Moment Tensor ◽  
Good Practice ◽  
Velocity Model ◽  
Moment Tensor Inversion ◽  
Phase Identification ◽  
Moment Tensors ◽  
Velocity Models ◽  
3D Velocity Model ◽  
1D Velocity Model

ABSTRACT Since 1991, induced earthquakes have been observed and linked to gas production in the Groningen field. Recorded waveforms are complex, resulting partly from a Zechstein salt layer overlying the reservoir and partly from free-surface reverberations, internal multiples, interface conversions, guided waves, and waves diving below the reservoir. Therefore, picking of polarities or amplitudes for use in moment tensor inversion is problematic, whereas phase identification may be circumvented employing full waveform techniques. Although moment tensors have become a basic tool to analyze earthquake sources, their uncertainties are rarely reported. We introduce a method for probabilistic moment tensor estimation and demonstrate its use on the basis of a single event within the Groningen field, concentrating on detailed tests of input data and inversion parameters to derive rules of good practice for moment tensor estimation of events recorded in the Groningen field. In addition to the moment tensor, event locations are provided. Hypocenters estimated simultaneously with moment tensors are often less sensitive to uncertainties in crustal structure, which is pertinent for the application to the Groningen field, because the task of relating earthquakes to specific faults hitherto suffers from a limited resolution of earthquake locations. Because of the probabilistic approach, parameter trade-offs, uncertainties, and ambiguities are mapped. In addition, the implemented bootstrap method implicitly accounts for modeling errors affecting every station and phase differently. A local 1D velocity model extracted from a full 3D velocity model yields more consistent results than other models applied previously. For all velocity models and combinations of input data tested, a shift in location of 1 km to the south is observed for the test event compared to the public catalog. A full moment tensor computed employing the local 1D velocity model features negative isotropic components and may be interpreted as normal fault and collapse at reservoir level.

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