Seismic Moment Tensor Inversion Research Articles

The Influence of a Local Fault Zone on High Energy Tremor Occurrence During Longwall Mining of a Coal Seam

Underground mining of coal seams in the Upper Silesian Coal Basin in Poland is accompanied by seismic activity of varying magnitude. The investigations which have been performed for several years distinguished high energy mine tremors connected directly with mining or coupled with geological structures, such as large faults. In mined seams, local fault zones occur. Faults in these zones are usually small, with throws comparable with coal seams thicknesses. Local fault zone may be responsible for the occurrence of high energy tremors as well as large faults, as presented in this article. An analysis of source mechanism of high energy tremors generated during longwall mining of the coal seam No. 510, with presence of a local fault zone, in one of the Polish hard coal mines in the Upper Silesian Coal Basin was performed. For this purpose, the seismic moment tensor inversion method was used. In most of foci, the process of shear predominated. Determined nodal plane parameters were correlated with parameters of faults forming the local fault zone. High energy tremors were generated mostly by dislocations on faults of the local fault zone. Weakening of roof rocks in the neighborhood of local fault zone takes an important role too, and was responsible for share of implosion in the focal mechanism.

HybridMT: A MATLAB/Shell Environment Package for Seismic Moment Tensor Inversion and Refinement

We present the software package hybridMT which allows performing seismic moment tensor inversion and refinement, optimized for earthquake data recorded by regional‐to‐local seismic networks as well as for acoustic emission activity. The provided software package is designed predominantly for use in MATLAB (see [Data and Resources][1])/shell environments. The algorithm uses first P ‐wave amplitudes to invert for unconstrained full, deviatoric, and double‐couple constrained moment tensors. Uncertainty assessment is performed by bootstrap resampling. The moment tensor inversion may be performed directly in the shell environment (by a dedicated command‐line tool) or conveniently through the MATLAB interface (m‐functions). In addition to moment tensor inversion, we also provide the MATLAB implementation of the hybrid moment tensor technique. This methodology increases the quality of calculated seismic moment tensors from events forming a spatial cluster by assessing and correcting for poorly known path and site effects. We tested hybridMT on synthetic datasets, acoustic emission data recorded during laboratory rock deformation experiments, and induced seismicity data from a geothermal reservoir. The package is supplemented with extensive documentation, tutorials, and a dedicated website. HybridMT is freely available and distributed under General Public License. [1]: #sec-10

Seismic moment tensor inversion using 3D velocity model and its application to the 2013 Lushan earthquake sequence

Source inversion of small-magnitude events such as aftershocks or mine collapses requires use of relatively high frequency seismic waveforms which are strongly affected by small-scale heterogeneities in the crust. In this study, we developed a new inversion method called gCAP3D for determining general moment tensor of a seismic source using Green's functions of 3D models. It inherits the advantageous features of the “Cut-and-Paste” (CAP) method to break a full seismogram into the Pnl and surface-wave segments and to allow time shift between observed and predicted waveforms. It uses grid search for 5 source parameters (relative strengths of the isotropic and compensated-linear-vector-dipole components and the strike, dip, and rake of the double-couple component) that minimize the waveform misfit. The scalar moment is estimated using the ratio of L2 norms of the data and synthetics. Focal depth can also be determined by repeating the inversion at different depths. We applied gCAP3D to the 2013 Ms 7.0 Lushan earthquake and its aftershocks using a 3D crustal-upper mantle velocity model derived from ambient noise tomography in the region. We first relocated the events using the double-difference method. We then used the finite-differences method and reciprocity principle to calculate Green's functions of the 3D model for 20 permanent broadband seismic stations within 200 km from the source region. We obtained moment tensors of the mainshock and 74 aftershocks ranging from Mw 5.2 to 3.4. The results show that the Lushan earthquake is a reverse faulting at a depth of 13–15 km on a plane dipping 40–47° to N46° W. Most of the aftershocks occurred off the main rupture plane and have similar focal mechanisms to the mainshock's, except in the proximity of the mainshock where the aftershocks' focal mechanisms display some variations.

Constraining geomechanical models by using microseismic-derived fractures from source mechanisms

Geomechanical modeling of hydraulic stimulations requires data to build and calibrate models to predict decline curves and other aspects of long-term reservoir performance. Initialization of these models requires knowledge of the preexisting fractures and geologic properties of the media. Orientations of different fracture sets, their intensities, and spacing, along with characterization of their size scales, critically impact geomechanical predictions of the stimulations in terms of proppant and fluid placement and the decline of reservoir productivity. With sufficient sampling of azimuths around the stimulation, the mechanisms and associated fracture planes and stress/strain conditions can be reconstructed through seismic-moment tensor inversion (SMTI) of recorded microseismic-event waveforms. At smaller scale lengths, signal-to-noise ratios can be low, and events might not be observed at high enough quality to permit SMTI. To extend the characterization of these fractures to smaller scales, a stochastic optimization algorithm is used, designed to search for optimally placed fractures in the reservoir that intersect with event locations while constraining their orientations from the same distribution observed at larger (SMTI-resolvable) length scales. Effectively, this technique allows for extension of the power law governing fracture distribution to smaller scales by invoking observed trends in self-similar behavior. In turn, characterization of the wider band of fractures in the reservoir provides necessary inputs into geomechanical models to predict fluid and proppant distributions from the full band of generated microseismicity and long-term behavior of the reservoir through decline-curve estimation.

Geomechanical conditions of causes of high-energy rock mass tremors determined based on the analysis of parameters of focal mechanisms

Abstract The aim of the research was to determine the cause of high-energy rock mass tremors (energy E ≥ 105 J) in the area of longwall H-2a located in seam 409/3 in Borynia-Zofiowka-Jastrzebie colliery, basing on the analysis of geological and mining conditions, seismic activity, focal mechanism and local stress field. The research employed the method of seismic moment tensor inversion which provides parameters of focal mechanism (percentage share of its components: isotropic, uniaxial compression or tension, shear component; trend and dip of nodal planes, directions of tension axes and compression stress). The parameters describe processes occurring in focuses of tremors and they are clearly linked with stress conditions in a given area. The conducted tests showed that the cause of occurrence of high-energy tremors and three rockbursts in lot H while mining seam 409/3 with longwall H-2a, was dynamic destruction of roof rocks which could displace towards the cavity created after mining the seam. An additional factor significantly magnifying the process was the share of stresses, which originate from the faults in the area, existing in the rock mass. Results of the research provided additional information to determine the degree of rockburst hazard in the area. Because of very dangerous work conditions (stress parameters reflect the rock mass of high shear strength, where dynamic influence of tremors is stronger) mining activity in longwall H-2a was terminated a few dozen metres earlier than it had been originally planned.

Joint location and source mechanism inversion of microseismic events: benchmarking on seismicity induced by hydraulic fracturing

SUMMARY Seismic monitoring can greatly benefit from imaging events with a low signal-to-noise ratio (SNR) as the number of the events with a low signal grows exponentially. One way to detect weaker events is improvement of a SNR by migration-type stacking of waveforms from multiple stations. We have developed a new method of location of seismic events that involves stackingofseismicphasesandamplitudesalongdiffractiontraveltimecurvestosuppressnoise and detect seismic events with a SNR lower than that on individual receivers. The stacking includes polarity correction based on a simultaneous seismic moment tensor inversion and detection algorithm on the stack function. We applied this method to locate microseismicity induced by hydraulic fracturing. First we calibrated the velocity model by locating perforation shots at known locations. Then we processed 3 d of data from microseismic monitoring of shale stimulation and benchmarked migration-type locations of the largest events that were manually located. The detected and located events induced by hydraulic fracturing in this case study are mostly shear events forming narrow bands along the maximum horizontal stress direction approximately 100 m above the injection intervals. The proposed technique is fully automated and feasible for real-time seismic monitoring.

Source mechanism of Vulcanian eruption at Tungurahua Volcano, Ecuador, derived from seismic moment tensor inversions

Source mechanisms of explosive volcanic eruptions are critical for understanding magmatic plumbing systems and magma transport. Tungurahua is a large andesitic stratovolcano where seismoacoustic data has been recorded over several years. In May 2010, an energetic eruption cycle began with a midsize Vulcanian explosion followed by swarms of explosive eruptions. The five-station seismoacoustic network recorded significant seismic and infrasonic signals from the explosions. Source mechanisms of 50 explosion earthquakes associated with Vulcanian explosions during this eruptive period are investigated here. The source centroid locations and geometries of explosive signals in the 10–2 s band were determined by full-waveform moment tensor inversion. The observed waveforms are well explained by a combination of volumetric moment tensor components and a single, vertical, downward force component. The source centroids are positioned about 1.5 km below and about 320 m north of the active crater. Eigenvalue and eigenvector analysis indicates that the source geometries can be described by a subhorizontal, thin ellipsoid representing a sill-like magma accumulation. Resultant source time histories show a repetitive sequence of inflation and deflation from event to event, indicating identical source processes frequently occurred over the period. The inflation/deflation in the deep source region may be the result of crack opening. Volatile bubble growth at depth opens a pathway for gases to escape and triggers shallow explosions at the summit crater. The associated downward single force is interpreted as an exchange of linear momentum between the source and the surrounding region during the escaping gas flow.

An improved method for seismic moment tensor inversion of acoustic emissions through assessment of sensor coupling and sensitivity to incidence angle

• We propose ultrasonic calibration technique of acoustic emission sensors. • Procedure useful when specimen and acoustic emission sensors are inside loading cell. • Acoustic emission waveforms corrected for coupling quality and incidence angle. • Full moment tensor inversion performed for Bentheim and Vosges sandstones . • Ultrasonic calibration compared with hybrid moment tensor technique.

The first Long Period earthquake detected in the background seismicity at Mt. Vesuvius

<p>The typical earthquakes occurring at Mt. Vesuvius are Volcano-Tectonic. On July 20, 2003, an unusual earthquake with low and narrow frequency content was detected. The seismograms presented an emergent onset and a nearly monochromatic spectrum at all stations of the Osservatorio Vesuviano (Istituto Nazionale di Geofisica e Vulcanologia) seismic network. The event was located at about 4 km b.s.l. close to the crater axis and an equivalent duration magnitude of 0.6 was estimated. The nature of this event was investigated by comparing its features with those of two typical Volcano-Tectonic earthquakes occurred inside the same source volume. We compared the spectral content calculating the spectrograms and the coda patterns using the Hilbert Transform. A Seismic Moment Tensor inversion was performed on the low frequency earthquake. The focal mechanisms for the two Volcano-Tectonic earthquakes were estimated with a classical technique and resulted compatible with the stress field acting on the volcano. Taking into account the clear differences with the typical Volcano-Tectonic events as well as the peculiarities retrieved from our analyses (monochromatic, low frequency spectral content, and sustained coda) and also some geochemical observations, we classify the unusual low frequency seismic event detected at Mt. Vesuvius as Long Period earthquake and propose that its origin could be linked to a pressure drop in the deep hydrothermal system.</p>

Quality assessment of microseismic event locations and traveltime picks using a multiplet analysis

The proliferation of hydraulic fracturing (frac) stimulation and other enhanced oil recovery techniques in unconventional plays has spurred interest in microseismic monitoring. Changes in stress in the subsurface produced by hydrocarbon production may induce brittle failure events. Many enhanced oil recovery techniques such as hydraulic frac stimulation or cyclic steam stimulation involve injecting large volumes of fluid at high pressure into a reservoir. Microseismic events, hereafter events, may illuminate the reach and effectiveness of enhanced recovery techniques within a reservoir. When array configuration is favorable, advanced analysis of microseismic data may provide additional information. For instance, seismic moment tensor inversion (Eaton and Forouhideh, 2010) may estimate the failure mode of an event. The aforementioned failure modes may include fracture-opening, shear, or fracture-closing events. Knowledge of the failure modes allows a detailed analysis of the effects of changing parameters such as steam injection temperature or well spacing.

A Quantitative Comparison between 1D and 3D Source Inversion Methodologies: Application to the Middle East

We present a quantitative comparison between seismic moment tensor (MT) inversion solutions using 1D and 3D synthetic seismograms at two frequency bands for events in the Middle East, to assess the effects of 3D models on source studies. Complex geology associated with the active continental convergent margin leads to a scarcity of reliable, available data, necessitating a thorough examination of solution stability and robustness to assure an accurate description of sources with well‐characterized source parameters. Solutions were calculated for 195 events ( M w>5.5) using a full‐waveform MT inversion matching both phase and amplitude. Seismic data processed at two frequency bands compares short‐ and long‐period performance for 1D and 3D synthetic seismograms. An improvement in fit between data and synthetics is seen using 3D over 1D synthetic seismograms, especially for complex body‐wave propagation and surface‐wave dispersion. At short periods, 3D synthetics provide a more robust solution compared with 1D, showing a reduction in error of the source mechanism. The percentage of double‐couple components increases with the addition of 3D structure and suggests the percentage of non‐double‐couple components is a result of poorly constrained Earth structure. Event solutions contained in the catalog (![Graphic][1] Table S1 in the electronic supplement to this paper) have an average cross‐correlation value of 0.87, with good amplitude ratios, and are improved (i.e., increased variance reduction) yet consistent with longer period solutions from the Global Centroid Moment Tensor (CMT) catalog. Online Material: Table of 184 event solutions from 3D moment tensor inversion. [1]: /embed/inline-graphic-1.gif

Seismic moment tensor inversion using a 3-D structural model: applications for the Australian region

SUMMARY There is significant seismic activity in the region around Australia, largely due to the plate boundaries to the north and to the east of the mainland. This activity results in serious seismic and tsunami hazard in the coastal areas of Australia. Hence seismicity is and will be monitored in real time by Geoscience Australia (GA), which uses a network of permanent broadband seismometers. Seismic moment tensor (MT) solutions are currently determined using 1-D, radially symmetric models of Earth and this requires augmentation by recording stations located outside of Australia. A 3-D model of the Australian continent developed recently using full waveform tomography now offers the opportunity to significantly improve the determination of MT solutions of earthquakes from tectonically active regions. A complete-waveform, time-domain MT inversion method has been developed using a point-source approximation. A series of synthetic tests using first a 1-D and then a 3-D structural model has been performed. The feasibility of deploying 3-D versus 1-D Earth structure for the inversion of seismic data has been studied and the advantages of using the 3-D structural model were illustrated with examples. The 3-D model is superior to the 1-D model, as a number of sensitivity tests show. The ultimate goal of this work is an automated MT inversion system in Australia relying on GA and other international stations, although more work remains to be done before the full implementation of such a scheme in real time.

Earthquake deformation in the northwestern Sierras Pampeanas of Argentina based on seismic waveform modelling

We investigate the seismic properties of modern crustal seismicity in the northwestern Sierras Pampeanas of the Andean retroarc region of Argentina. We modelled the complete regional seismic broadband waveforms of two crustal earthquakes that occurred in the Sierra de Velasco on 28 May 2002 and in the Sierra de Ambato on 7 September 2004. For each earthquake we obtained the seismic moment tensor inversion (SMTI) and tested for its focal depth. Our results indicate mainly thrust focal mechanism solutions of magnitudes Mw 5.8 and 6.2 and focal depths of 10 and 8 km, respectively. These results represent the larger seismicity and shallower focal depths in the last 100 years in this region. The SMTI 2002 and 2004 solutions are consistent with previous determinations for crustal seismicity in this region that also used seismic waveform modelling. Taken together, the results for crustal seismicity of magnitudes ≥5.0 in the last 30 years are consistent with an average P-axis horizontally oriented by an azimuth of 125◦ and T-axis orientation of azimuth 241 ◦ and plunge 58 ◦ . This modern crustal seismicity and the histori

Continuous hypocenter and source mechanism inversion via a Green's function-based matching pursuit algorithm

The hydraulic fracturing of rock formations bearing oil and gas is a process that aims to improve well productivity. The breaking of rocks releases seismic energy that is recorded by stations usually located in nearby wells. By processing these recordings, the hypocenters of induced microseismic events are retrieved and interpreted to estimate the fractured volume. Several techniques have been developed to determine hypocenters; the most common are based in the inversion of P- and S-wave time picks from multiple stations (Pujol, 2004). There are also procedures that involve, for example, the back propagation in time of the recorded wavefields (Gajewski and Tessmer, 2005). Besides the hypocenter location of microseismic events, there is additional information embedded in the seismic recordings: the source mechanism, which is expressed via the seismic moment tensor (SMT). Not as common as the estimation of the hypocenter location, the SMT of induced microseismic events is also estimated from monitoring records (e.g., Nolen-Hoeksema and Ruff, 2001; Jechumtalova and Eisner, 2008). The SMT provides an additional source of information for understanding the fracturing process. A quasi real-time system for simultaneous event location and SMT inversion can reduce the processing and interpretation turnaround times. More notably, such a system could facilitate a realistic integration of microseismic geophysical data to significant decisions that are made during engineering operations such as fracturing.

Effects of complicated 3-D rupture geometries on earthquake ground motion and their implications: a numerical study

SUMMARY We present a numerical study of the effects of geometrically complicated 3-D ruptures on near-source ground motions. In most of the kinematic and dynamic rupture modelling studies or seismic moment tensor and slip inversions the strong assumption of a perfectly planar fault is made. However, it is known from geological field studies that real fault traces are not planar but characterized by relatively strong deflections, bends and other irregularities. In this paper we, investigate the effects of such non-planar earthquake ruptures on ground motion modelling in comparison to their equivalent planar ones. For this purpose we apply the highly accurate Discontinuous Galerkin method that is capable of incorporating the geometry of complicated non-planar rupture surfaces by a set of double couple point sources that do not have to coincide with the mesh vertices. We generate a set of kinematic rupture models characterized by random spatial deflections with various correlation lengths and root mean square values. These deflections then determine the associated spatial strike and dip variations. We find that the deflected rupture models have the same seismic moment tensor as the perfectly planar one, however, with a reduced scalar moment, which we correct for. After a sound validation of our modelling approach, we present the effects of the deflections on synthetic velocity seismograms computed in the vicinity of the rupture. We observe that these geometrical irregularities do not just lead to high frequency effects but can strongly affect the synthetics in the whole frequency band. Finally, we discuss our observations in detail and conclude that the correct incorporation of the geometrical properties such as local strike and dip variations of the rupture surface is an important issue. We also discuss possible implications for some seismological fields, such as strong-motion simulations or seismic moment tensor and slip inversions, where these results might have significant consequences.

Crustal structure of the south-central Andes Cordillera and backarc region from regional waveform modelling

SUMMARY We investigate the crustal structure in the Andes Cordillera and its backarc region using regional broadband waveforms from crustal earthquakes. We consider seismic waveforms recorded at regional distances by the CHile-ARgentina Geophysical Experiment (CHARGE) during 2000‐2002 and utilize previous seismic moment tensor inversion results. For each single station-earthquake pair, we fixed the source parameters and performed forward waveform modelling using ray paths that sample the crust of the highest elevation Cordillera and the accreted terranes in the backarc region. Our investigation indicates that synthetic seismograms for our earthquake-station geometry are most sensitive to crustal parameters and less sensitive to mantle parameters. We performed a grid search around crustal thickness, P-wave seismic velocity (Vp) and P -t oS-wave seismic velocity ratio (Vp/Vs), fixing mantle parameters. We evaluated this waveform analysis by estimating an average correlation coefficient between observed and synthetic data over the three broadband components. We identified all acceptable crustal models that correspond to high correlation coefficients that provide best overall seismogram fits for the data and synthetic waveforms filtered mainly between 10 and 80 s. Our results indicate along strike variations in the crustal structure for the north‐south high Cordillera with higher P-wave velocity and thickness in the northern segment (north of 33 ◦ S), and persistently high Vp/Vs ratio (>1.85) in both segments. This is consistent with a colder mafic composition for the northern segment and a region of crustal thickening above the flat slab region. In contrast, the results for the current volcanic arc (south of 33 ◦ S) agree with a warmer crust consistent with partial melt related to Quaternary volcanism presumably of an intermediate to mafic composition. A distinctive feature in the backarc region is the marked contrast between the seismic properties of the Cuyania and Pampia terranes that correlates with their heterogeneous crustal composition. The Cuyania terrane, composed of mafic-ultramafic rocks, exhibits high Vp, high Vp/Vs and a thicker layered crust versus the thinner more quartzrich crust of the eastern Sierras Pampeanas associated with low Vp and low Vp/Vs. These differences may have some effect on the mechanism that unevenly generates crustal seismicity in the upper ∼30 km in this active compressional region. In particular, the seismic properties of the Cuyania terrane, which shows evidence for a high Vp and high Vp/Vs crust, may be reflecting the complex tectonic evolution history of this terrane including accretion-rifting and re-accretion processes since the Palaeozoic that promote a high level of crustal seismicity in the upper ∼30 km, enhanced by the flat slab subduction in the segment between 31 ◦ S and 32 ◦ S. Another possible mechanism could be directly related to the presence of a strong lower crust above the flat slab that efficiently transfer stresses from the slab to the upper crust generating higher seismicity in the Cuyania terrane between 30 ◦ S and 34 ◦ S.

Specific features of surface wave radiation by a shallow source

The uncertainty of the seismic moment tensor inversion from records of long period surface waves radiated by a shallow source is considered. The special cases of sources of pure thrust, normal, and strike-slip faults are examined in detail. Results of numerical modeling of Love and Rayleigh wave radiation patterns and frequency dependences of the radiation intensity are presented for these types of sources. It is shown that, in the general case, the focal mechanism and seismic moment of a shallow double couple can be uniquely determined from long period surface waves only if one of the nodal planes is subhorizontal. The threshold (maximum) value of the dip angle of this plane is determined by the source depth, the spectral range of observed surface waves, and the model structure in the vicinity of the source.

Active tectonics in Central Italy: constraints from surface wave tomography and source moment tensor inversion

We investigate the lithosphere–asthenosphere structure and active tectonics of Central Italy, with emphasis on the Umbria–Marche area, by means of surface wave tomography and seismic moment tensor inversion. The data include: a large number of short period local and regional group velocity measurements sampling the Umbria–Marche Apennines and the Adria margin, respectively; incorporation of published phase velocity measurements sampling Italy and surroundings; results from deep seismic soundings which go through the Umbria–Marche area. The local group velocity maps, covering the area reactivated by the 1997–1998 Umbria–Marche earthquake sequence, suggest an intimate relationship between the lateral earth structure variations and the distribution of the active fault systems and related sedimentary basins. The upper crustal models reveal the importance of inherited compressional tectonics on the recent extensional deformation and associated seismic activity. Source inversion studies of the main events of the 1997 earthquake sequence show the dominance of normal faulting mechanisms, whereas selected aftershocks between the fault segments, at the step-over, reveal that the prevailing deformation is of strike-slip faulting type. At the regional scale, the crust exhibits clear layering and varies in thickness from about 25 km below the Tuscan Metamorphic Complex (TMC), to about 30 km below the Val Tiberina extensional thick sedimentary basin and reaches about 35 km below the Umbria–Marche geological domain (UMD). The lithospheric mantle (lid) is thin (about 30 km) below TMC, while it is about 70 km thick below UMD. A lithospheric root about 120 km wide, between the TMC and UMD, reaches a depth of at least 130 km. A low-velocity zone, defined mantle wedge ( V S less than 4.2 km/s) in the uppermost mantle overlying the high velocity lid is detached. This wedge is about 20 km thick and decouples the underlying lid from the crust. The retrieved crust and upper mantle structure beneath Central Italy is in agreement with Bouguer anomaly and heat flow data and supports a delamination process. The high velocity upper mantle underlying the mantle wedge is inferred to be subcrustal lithospheric material delaminated from the overlying crust.

Regional distance seismic moment tensors of nuclear explosions

Nuclear explosions, because of their known location, depth and theoretical source mechanism, provide a means to explore the resolution of non-double-couple and isotropic seismic moment tensors. We perform seismic moment tensor inversions on long-period (50–20 s), three-component velocity seismograms from the Caltech TERRAscope network and the Berkeley Digital Seismic Network (BDSN) to determine best-fitting double-couple, isotropic plus double-couple, deviatoric and full-moment tensor source mechanisms for the Little Skull Mountain Earthquake and three large ( M L≥5.5, M W≥4.5) Nevada Test Site (NTS) nuclear explosions (JUNCTION, MONTELLO and BEXAR). The significance of solutions with higher degrees of freedom is evaluated using the F-test. The stability of the moment tensor solutions for variations in station configuration is investigated using a cross-validation method. Our results show that strongly non-double-couple seismic moment tensors and shallow source depth characterize the nuclear explosions. The full-moment tensor inversions recover a volume increase. However, our analysis indicates that the improvement in fit afforded by the extra degree of freedom is not statistically significant due to the similarity of the vertical compensated linear vector dipole (CLVD) and isotropic surface wave Green's functions at these periods. An isotropic plus double-couple source model was found to provide the same level of fit as the deviatoric moment tensor inversions. Determination of the nonisotropic source mechanism is not unique and we discuss our results with respect to the proposed source models for NTS. While the results of this study indicate that regional distance seismic moment tensor analysis is not suitable for directly discriminating nuclear explosions from earthquakes, the shallow source depth and non-double-couple seismic moment tensors obtained for these events suggest that it may be useful for identifying suspect events for further screening.

Reliability of Seismic Moment Tensor Inversions for Induced Microseismicity at Kidd Mine, Ontario

Reliability of Seismic Moment Tensor Inversions for Induced Microseismicity at Kidd Mine, Ontario