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 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.

Fast acquisition of focal mechanism based on statistical analysis

2020 ◽  
Author(s):  
Marisol Monterrubio-Velasco ◽  
José Carlos Carrasco-Jimenez ◽  
Otilio Rojas ◽  
Juan Esteban Rodríguez ◽  
Josep de la Puente
Keyword(s):  
Focal Mechanism ◽  
Moment Tensor ◽  
Early Warning Systems ◽  
Spatial Dimension ◽  
Model Parameters ◽  
Data Set ◽  
Earthquake Parameters ◽  
Ground Shaking ◽  
Tsunami Early Warning ◽  
Urgent Computing

<p>Earthquake and tsunami early warning systems and post-event urgent computing simulations require of fast and accurate quantification of earthquake parameters such as magnitude, location and Focal Mechanism (FM). Methodologies to estimate earthquake location and magnitude are well-established and in place. However, automatic solutions of FMs are not always provided by operational institutions and are, in some cases, available only after a time-consuming inversion of the wave-forms needed to determine the moment tensor components. This precludes urgent seismic simulations, which aim at providing ground shaking maps with severe time constraints. We propose a new strategy for fast (<60 s) determination of FM based on historical data sets, tested it at five different active seismic regions, Japan, New Zealand, California, Iceland, and Italy. The methodology includes the k-nearest neighbor's algorithm in a spatial dimension domain to search the most similar FMs between the data set. In our research, we focus on moderate to large earthquakes. The comparison algorithm includes the four closest events, and also a hypothetical event building by the median values of strike, dip, and rake of the k-neighbors. The validation stage includes the minimum rotated angle measure to compute the similitude between a pair of FMs. We find three model parameters, such as the minimum number of neighbors, the threshold radius that defines the neighboring sphere, and the magnitude threshold, that could improve the statistical similitude results. Our fast methodology has a 75%-90% agreement with traditional inversion mechanisms, depending on the particular tectonic region and dataset size. Our work is a key component of an urgent computing workflow, where the FM information will be used as input for ground motion simulations. Future work will assess the sensitivity of FM uncertainty in the resulting ground-shaking maps.</p>

Seismic source inversion using Hamiltonian Monte Carlo and a 3-D Earth model in the Japanese Islands

2020 ◽  
Author(s):  
Saulė Simutė ◽  
Lion Krischer ◽  
Christian Boehm ◽  
Martin Vallée ◽  
Andreas Fichtner
Keyword(s):  
Monte Carlo ◽  
Moment Tensor ◽  
Seismic Source ◽  
Monte Carlo Algorithm ◽  
Earth Model ◽  
Model Parameters ◽  
Hamiltonian Monte Carlo ◽  
Double Couple ◽  
Full Moment Tensor ◽  
Japanese Islands

<p>We present a proof-of-concept catalogue of full-waveform seismic source solutions for the Japanese Islands area. Our method is based on the Bayesian inference of source parameters and a tomographically derived heterogeneous Earth model, used to compute Green’s strain tensors. We infer the full moment tensor, location and centroid time of the seismic events in the study area.</p><p>To compute spatial derivatives of Green’s functions, we use a previously derived regional Earth model (Simutė et al., 2016). The model is radially anisotropic, visco-elastic, and fully heterogeneous. It was constructed using full waveforms in the period band of 15–80 s.</p><p>Green’s strains are computed numerically with the spectral-element solver SES3D (Gokhberg & Fichtner, 2016). We exploit reciprocity, and by treating seismic stations as virtual sources we compute and store the wavefield across the domain. This gives us a strain database for all potential source-receiver pairs. We store the wavefield for more than 50 F-net broadband stations (www.fnet.bosai.go.jp). By assuming an impulse response as the source time function, the displacements are then promptly obtained by linear combination of the pre-computed strains scaled by the moment tensor elements.</p><p>With a feasible number of model parameters and the fast forward problem we infer the unknowns in a Bayesian framework. The fully probabilistic approach allows us to obtain uncertainty information as well as inter-parameter trade-offs. The sampling is performed with a variant of the Hamiltonian Monte Carlo algorithm, which we developed previously (Fichtner and Simutė, 2017). We apply an L2 misfit on waveform data, and we work in the period band of 15–80 s.</p><p>We jointly infer three location parameters, timing and moment tensor components. We present two sets of source solutions: 1) full moment tensor solutions, where the trace is free to vary away from zero, and 2) moment tensor solutions with the isotropic part constrained to be zero. In particular, we study events with significant non-double-couple component. Preliminary results of ~Mw 5 shallow to intermediate depth events indicate that proper incorporation of 3-D Earth structure results in solutions becoming more double-couple like. We also find that improving the Global CMT solutions in terms of waveform fit requires a very good 3-D Earth model and is not trivial.</p>

scholarly journals A focal mechanism catalogue of earthquakes that occurred in the southeastern Alps and surrounding areas from 1928–2019

2021 ◽  
Vol 13 (5) ◽  
pp. 2245-2258
Author(s):  
Angela Saraò ◽  
Monica Sugan ◽  
Gianni Bressan ◽  
Gianfranco Renner ◽  
Andrea Restivo
Keyword(s):  
Focal Mechanism ◽  
Moment Tensor ◽  
Active Regions ◽  
Focal Mechanisms ◽  
Seismic Moment Tensor ◽  
Fault Plane Solutions ◽  
First Arrival ◽  
Populated Region ◽  
Surrounding Areas ◽  
Catalogue Of Earthquakes

Abstract. We present a focal mechanism catalogue of earthquakes that occurred in the southeastern Alps and surrounding areas from 1928 to 2019. The area involved in the process of convergence between the Adria microplate and Eurasia is one of the most seismically active regions in the Alpine Belt. The seismicity is minor, with the Ms= 6.5 Friuli earthquake being the strongest event recorded in the area, but the seismic risk is relevant because it is a highly populated region. For this reason, numerous studies have been carried out over time to investigate the stress field and the geodynamic characteristics of the region using focal mechanisms. To provide a comprehensive set of revised information, which is challenging to build quickly because the data are dispersed over many papers, we collected and revised the focal mechanisms that were previously published in the literature. Additionally, depending on the data quality and availability, we computed new focal mechanisms by first arrival polarity inversion or seismic moment tensor. Finally, we merged all the fault plane solutions to obtain a catalogue for a selection of 772 earthquakes with 1.8≤M≤6.5. For each earthquake, we reported all the available focal mechanisms obtained by different authors. We also suggested a preferred solution for users who need information provided expeditiously. The catalogue (https://doi.org/10.5281/zenodo.4660412; Saraò et al., 2021) is given as the Supplement of this paper and will be updated periodically (https://doi.org/10.5281/zenodo.4284970).

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.

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>

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.

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