Reliability tests of moment tensor inversion of anthropogenic seismicity

2021 ◽  
Author(s):  
Anna Tymińska ◽  
Grzegorz Lizurek
Keyword(s):  
Moment Tensor ◽  
P Wave ◽  
Quality Data ◽  
Seismic Moment Tensor ◽  
Signal Ratio ◽  
Amplitude Inversion ◽  
Double Couple ◽  
Anthropogenic Seismicity ◽  
Determine Mechanism ◽  
Seismic Networks

<p>Seismic moment tensor becomes part of basic seismic data processing. For anthropogenic events mostly common and available method to determine mechanism is amplitude inversion. However essential for correct amplitude inversion are good quality data. Factors commonly occurring in anthropogenic seismicity like high noise to signal ratio, low magnitude and shortage of seismic stations with unfavorable focal coverage can introduce undetected errors to inversion solution. In this work, synthetic tests for two seismic networks are presented to examine the reliability of P-wave first peak amplitude inversion for these areas. The synthetic tests of the noise influence on the results of full MT solutions were carried out for two surface networks monitoring anthropogenic seismicity: VERIS network in Vietnam and LUMINEOS network in Poland. Various mechanisms with double couple component variability from 10% to 100% were considered to take into account mechanisms caused by different types of human activity. High variability of solutions in tests shows that some spurious components cannot be avoided in full moment tensor solutions obtained for presented networks in certain cases.</p><p>This work was partially supported by research project no. 2017/27/B/ST10/01267, funded by the National Science Centre, Poland, under agreement no. UMO-2017/27/B/ST10/01267.</p>

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

<p>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.</p><p>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 (SH<sub>max</sub>) 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.</p>

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.

scholarly journals KAMCHATKA AND COMMANDER ISLANDS

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.

scholarly journals Closing crack earthquakes within the Krafla caldera, North Iceland

2016 ◽  
Vol 207 (2) ◽  
pp. 1137-1141 ◽  
Author(s):  
Zoë K. Mildon ◽  
David J. Pugh ◽  
Jon Tarasewicz ◽  
Robert S. White ◽  
Bryndís Brandsdóttir
Keyword(s):  
Signal To Noise Ratio ◽  
Moment Tensor ◽  
Full Range ◽  
P Wave ◽  
High Signal ◽  
Closing Crack ◽  
Double Couple ◽  
Moment Tensor Analysis ◽  
First Arrival ◽  
Microseismic Activity

Abstract Moment tensor analysis with a Bayesian approach was used to analyse a non-double-couple (non-DC) earthquake (Mw ∼ 1) with a high isotropic (implosive) component within the Krafla caldera, Iceland. We deduce that the earthquake was generated by a closing crack at depth. The event is well located, with high signal-to-noise ratio and shows dilatational P-wave first arrivals at all stations where the first arrival can be picked with confidence. Coverage of the focal sphere is comprehensive and the source mechanism stable across the full range of uncertainties. The non-DC event lies within a cluster of microseismic activity including many DC events. Hence, we conclude that it is a true non-DC closing crack earthquake as a result of geothermal utilization and observed magma chamber deflation in the region at present.

scholarly journals SEISMICITY of KAMCHATKA and COMMANDER ISLANDS in 2015

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.

scholarly journals Micro-Crack Mechanism in the Fracture Evolution of Saturated Granite and Enlightenment to the Precursors of Instability

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4595 ◽  
Author(s):  
Longjun Dong ◽  
Yihan Zhang ◽  
Ju Ma
Keyword(s):  
Moment Tensor ◽  
Average Frequency ◽  
Source Model ◽  
P Wave ◽  
Uniaxial Compression Test ◽  
Rock Fracturing ◽  
Fracture Evolution ◽  
Double Couple ◽  
Fracture Size ◽  
The Moment

To explore the potential precursors of rock instability, it is necessary to clarify the mechanism of micro-crack from fracturing to failure, which involves the evolution of fracture size, orientation, source model, and their relationships to the loading. The waveforms of acoustic emission (AE) recorded by the sensor network attached rock sample during laboratory tests provide a data basis for solving these problems, since these observations are directly related to the characteristics of the fracturing sources. Firstly, we investigated the source mechanism, looking at the rise angle and the average frequency (RA-AF) trends during five loading stages in a uniaxial compression test. Results show that the proportion of shear events significantly increases when approaching instability. Secondly, we calculated the moment tensor for each event, considering the uncertainties of P-wave polarity, azimuth, and the takeoff angles of the rays. Moment tensor solutions suggest that there are obviously more crack events than shear events in all loading stages. Moment tensor evolutions confirmed that the decreasing of isotropic component and the increment of double-couple can be used as precursors of rock fracturing development. Considering the limitations of these two methods, it is suggested that we should be concerned more about the proportions of individual failure components and their evolutions over time, instead of absolutely classifying the events into a certain source type.

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 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.

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