S-wave Amplitude Research Articles

SD+SV4 diagnosis of left ventricular hypertrophy, a revaluation of ECG criterion by cardiac magnetic resonance imaging.

BackgroudPresent electrocardiogram (ECG) criteria for diagnosing left ventricular hypertrophy (LVH) usually have low sensitivity, while the newly proposed SD + SV4 criterion, namely the deepest S‐wave amplitude in any lead (SD) plus SV4 amplitude, has been reported to have higher sensitivity and accuracy compared with other existing criteria. We aimed to further evaluate the diagnostic value of the SD + SV4 criterion in reference to the gold standard cardiac magnetic resonance imaging (CMR) in LVH diagnosis.MethodsThis retrospective study enrolled 138 patients who received CMR examination—60 patients with reduced ejection fraction (EF) and 78 patients with preserved EF. The left ventricular mass index (LVMI) measured by CMR was used as the gold standard for diagnosing LVH.ResultThe diagnostic value of the SD + SV4 criterion was compared with other 4 commonly used criteria. By CMR, 29 out of 138 people (21%) were diagnosed with LVH in reference to CMR. The SD + SV4 criterion had markedly higher sensitivity in diagnosing LVH compared with other criteria, but no higher specificity. There was no significant difference in area under receiver operating characteristic (ROC) curve among these criteria. The SD + SV4 criterion was not markedly consistent with CMR in diagnosing LVH. Compared to the other criteria, the SD + SV4 criterion had the highest sensitivity in patients with reduced ejection fraction; however, the area under the curve (AUC) of the SD + SV4 criterion in patients with reduced EF was significantly lower than in patients with preserved EF.ConclusionThe newly proposed SD + SV4 criterion did not have a better diagnostic value compared with other existing criteria, and the statistical power of the SD + SV4 criterion was influenced by EF.

Precordial ECG Amplitudes in the Days After Birth: Electrocardiographic Changes During Transition from Fetal to Neonatal Circulation.

During the first month of life, the relation between right and left ventricular function is markedly altered. We aimed at describing the electrocardiographic transition from fetal to neonatal circulation by investigating changes in R- and S-wave amplitudes in V1 and V6 during the first 4 weeks of life. This study is part of the prospective, population-based Copenhagen Baby HeartStudy offering cardiac evaluation to newborns within 28days from birth. ECGs were obtained and analyzed using a computerized algorithm. A total of 14,577 newborns (52% boys), median age of 11.0days, were included. All had normal echocardiograms. Within 28days from birth, the amplitudes in V1 decreased: R-V1 (1262µV day0; 947µV day28, p < 0.001) and S-V1 (1240µV day0; 473µV day28, p < 0.001). An increase was observed for R-V6 (825µV day0; 1196µV day28, p = 0.002), while S-V6 decreased (830µV day0; 634µV day28, p = 0.003). For all amplitudes, interindividual variation was large (up to 20 times). The amplitudes were not affected by sex (p > 0.05), but R-V1, R-V6, and S-V6 positively correlated with newborn weight (p < 0.01). R-V1 and S-V6 showed positive correlation with gestational age (p < 0.05). In conclusion,systematic analyses of ECGs from healthy newborns showed significant decreases in R-V1, S-V1, and S-V6 amplitudes, while R-V6 increased. Interindividual variation was large, making ECGs unlikely as a sensitive tool for diagnosing congenital heart diseases. Our data may serve as updated, digitalized reference values in newborns.

SPECTRAL and FOCAL PARAMETERS of NORTHERN CAUCASUSEARTHQUAKES

Dynamic sources parameters of 21 earthquakes of the North Caucasus for 2014 with КР=9.5–11.5, determined from 44 S-wave amplitude spectra are analyzed. Records of three regional digital seismic stations, “Anapa”, “Kislovodsk” and “Sochi”, located no more than 300 km from the sources are used. For the environment near these stations, the values of the frequency-dependent Q-factor, necessary for recalculating the station spectra to the focal ones, were obtained earlier by O.V. Pavlenko. In 2014, the majority of earthquakes studied were located in the Eastern Caucasus. The dependence between log M0 and КР for this zone was constructed using the data for 2010–2013. Compared to the similar equation for the entire Caucasus (Riznichenko et all., 1976), this dependence is in a good agreement with respect to the free term, but differs by the slope.

Robust Empirical Time–Frequency Relations for Seismic Spectral Amplitudes, Part 2: Model Uncertainty and Optimal Parameterization

ABSTRACTIn a companion article, Safarshahi and Morozov (2020) argued that construction of distance- and frequency-dependent models for seismic-wave amplitudes should include four general elements: (1) a sufficiently detailed (parametric or nonparametric) model of frequency-independent spreading, capturing all essential features of observations; (2) model parameters with well-defined and nonoverlapping physical meanings; (3) joint inversion for multiple parameters, including the geometrical spreading, Q, κ, and source and receiver couplings; and (4) the use of additional dataset-specific criteria of model quality, while fitting the logarithms of seismic amplitudes. Some of these elements are present in existing models, but, taken together, they are poorly understood and require an integrated approach. Such an approach was illustrated by detailed analysis of an S-wave amplitude dataset from southern Iran. The resulting model is based on a frequency-independent Q, and matches the data closer than conventional models and across the entire epicentral-distance range. Here, we complete the analysis of this model by evaluating the uncertainties and trade-offs of its parameters. Two types of trade-offs are differentiated: one caused by a (possibly) limited model parameterization and the second due to statistical data errors. Data bootstrapping shows that with adequate parameterization, attenuation properties Q, κ, and geometrical spreading parameters are resolved well and show moderate trade-offs due to measurement errors. Using the principal component analysis of these trade-offs, an optimal (trade-off free) parameterization of seismic amplitudes is obtained. By contrast, when assuming theoretical values for certain model parameters and using multistep inversion procedures (as commonly done), parameter trade-offs increase dramatically and become difficult to assess. In particular, the frequency-dependent Q correlates with the distribution of the source and receiver-site factors, and also with biases in the resulting median data residuals. In the new model, these trade-offs are removed using an improved parameterization of geometrical spreading, constant Q, and model quality constraints.

Robust Empirical Time–Frequency Relations for Seismic Spectral Amplitudes, Part 1: Application to RegionalSWaves in Southeastern Iran

ABSTRACTEmpirical models of geometrical-, Q-, t-star, and kappa-type attenuation of seismic waves and ground-motion prediction equations (GMPEs) are viewed as cases of a common empirical standard model describing variation of wave amplitudes with time and frequency. Compared with existing parametric and nonparametric approaches, several new features are included in this model: (1) flexible empirical parameterization with possible nonmonotonous time or distance dependencies; (2) joint inversion for time or distance and frequency dependencies, source spectra, site responses, kappas, and Q; (3) additional constraints removing spurious correlations of model parameters and data residuals with source–receiver distances and frequencies; (4) possible kappa terms for sources as well as for receivers; (5) orientation-independent horizontal- and three-component amplitudes; and (6) adaptive filtering to reduce noise effects. The approach is applied to local and regional S-wave amplitudes in southeastern Iran. Comparisons with previous studies show that conventional attenuation models often contain method-specific biases caused by limited parameterizations of frequency-independent amplitude decays and assumptions about the models, such as smoothness of amplitude variations. Without such assumptions, the frequency-independent spreading of S waves is much faster than inferred by conventional modeling. For example, transverse-component amplitudes decrease with travel time t as about t−1.8 at distances closer than 90 km and as t−2.5 beyond 115 km. The rapid amplitude decay at larger distances could be caused by scattering within the near surface. From about 90 to 115 km distances, the amplitude increases by a factor of about 3, which could be due to reflections from the Moho and within the crust. With more accurate geometrical-spreading and kappa models, the Q factor for the study area is frequency independent and exceeds 2000. The frequency-independent and Q-type attenuation for vertical-component and multicomponent amplitudes is somewhat weaker than for the horizontal components. These observations appear to be general and likely apply to other areas.

Modified Precordial Lead R-Wave Deflection Interval Predicts Left- and Right-Sided Idiopathic Outflow Tract Ventricular Arrhythmias.

This study evaluated if modifying electrocardiographic (ECG) precordial leads to a higher intercostal position improved the accuracy of outflow tract ventricular arrhythmia (OTVA) localization. Precordial ECG prediction algorithms that use a standard lead configuration localize OTVA with variable accuracy. Patients who underwent OTVA ablation were prospectively enrolled to have a standard and modified (high) precordial ECG. R- and S-wave amplitudes and intervals were measured to develop an algorithm that differentiated the right ventricular outflow tract (RVOT) and the left ventricular outflow tract (LVOT) with high accuracy-the modified lead R-wave deflection interval (RWDI). This interval was defined from the earliest QRS onset (using all modified leads) to the lead with longest R-wave deflection. The RWDI was compared with all other ECG algorithms. A total of 50 patients (38 women; mean age 51 ± 17 years) had successful catheter ablation for OTVA (RVOT 60%, LVOT 40%). The modified lead RWDI was significantly shorter in the RVOT group (18.5ms, interquartile range 25th to 75th percentile [IQR25-75]: 0 to 29.5ms) compared with the LVOT group (67.5ms, IQR25-75: 56.5 to 77ms; p<0.05). Using a RWDI≤40ms to predict an RVOT focus, the sensitivity and specificity of the modified lead RWDI were 100% and 95%, respectively; the area under the receiver-operating characteristic curve was 0.96. This was superior to all previously developed algorithms. In a computed tomography analysis (n=50), the modified leads were significantly closer to the outflow tracts compared with the standard precordial leads. The modified lead RWDI is a simple, easily interpretable algorithm that can potentially differentiate a right- or left-sided origin of OTVA with high accuracy.

Classification of sinus rhythm single potential morphology in patients with mitral valve disease.

AimsThe morphology of unipolar single potentials (SPs) contains information on intra-atrial conduction disorders and possibly the substrate underlying atrial fibrillation (AF). This study examined the impact of AF episodes on features of SP morphology during sinus rhythm (SR) in patients with mitral valve disease.Methods and resultsIntraoperative epicardial mapping (interelectrode distance 2 mm) of the right and left atrium (RA, LA), Bachmann’s bundle (BB), and pulmonary vein area (PVA) was performed in 67 patients (27 male, 67 ± 11 years) with or without a history of paroxysmal AF (PAF). Unipolar SPs were classified according to their differences in relative R- and S-wave amplitude ratios. A clear predominance of S-waves was observed at BB and the RA in both the no AF and PAF groups (BB 88.8% vs. 85.9%, RA 92.1% vs. 85.1%, respectively). Potential voltages at the RA, BB, and PVA were significantly lower in the PAF group (P < 0.001 for each) and were mainly determined by the size of the S-waves amplitudes. The largest difference in S-wave amplitudes was found at BB; the S-wave amplitude was lower in the PAF group [4.08 (2.45–6.13) mV vs. 2.94 (1.40–4.75) mV; P < 0.001]. In addition, conduction velocity (CV) at BB was lower as well [0.97 (0.70–1.21) m/s vs. 0.89 (0.62–1.16) m/s, P < 0.001].ConclusionThough excitation of the atria during SR is heterogeneously disrupted, a history of AF is characterized by decreased SP amplitudes at BB due to loss of S-wave amplitudes and decreased CV. This suggests that SP morphology could provide additional information on wavefront propagation.

Evaluation of relationships between results of electrocardiography and echocardiography in 341 chimpanzees (Pan troglodytes).

To examine potential relationships between ECG characteristics and echocardiographic measures of cardiac structure in chimpanzees (Pan troglodytes). 341 chimpanzees (175 males and 166 females) from 5 sanctuaries and 2 zoological collections. Chimpanzees were anesthetized for routine health examinations between May 2011 and July 2017 as part of the International Primate Heart Project and, during the same anesthetic events, underwent 12-lead ECG and transthoracic echocardiographic assessments. Relationships between results for ECG and those for echocardiographic measures of atrial areas, left ventricular internal diameter in diastole (LVIDd), and mean left ventricular wall thicknesses (MLVWT) were assessed with correlational analysis, then multiple linear regression analyses were used to create hierarchical models to predict cardiac structure from ECG findings. Findings indicated correlations (r = -0.231 to 0.310) between results for ECG variables and echocardiographic measures. The duration and amplitude of P waves in lead II had the strongest correlations with atrial areas. The Sokolow-Lyon criteria, QRS-complex duration, and R-wave amplitude in leads V6 and II had the strongest correlations with MLVWT, whereas the Sokolow-Lyon criteria, QRS-complex duration, and S-wave amplitude in leads V2 and V1 had the strongest correlations with LVIDd. However, the ECG predictive models that were generated only accounted for 17%, 7%, 11%, and 8% of the variance in the right atrial end-systolic area, left atrial end-systolic area, MLVWT, and LVIDd, respectively. Results indicated that relationships existed between ECG findings and cardiac morphology in the chimpanzees of the present study; however, further research is required to examine whether the predictive models generated can be modified to improve their clinical utility.

P988Classification of sinus rhythm potential morphology in patients with mitral valve disease

Abstract Funding Acknowledgements CVON-AFFIP [grant number 914728], NWO-Vidi [grant number 91717339], Biosense Webster USA [ICD 783454] and Medical Delta Background The morphology of atrial electrograms (EGMs) contains information on intra-atrial conduction and hence conduction disorders giving rise to development of atrial fibrillation (AF). Prior studies have indeed demonstrated that areas of abnormal EGM morphologies are indicators of electropathology underlying AF. By creating an electrical signal profile obtained from high-resolution mapping data of the entire atria during AF -a so-called AF Fingerprint- the severity and extensiveness of electropathology can be determined. The first step towards development of an AF Fingerprint, is understanding characteristics of EGM morphology during sinus rhythm (SR). Objective The goal of this study is to examine EGM morphology at a high resolution scale during SR in patients with mitral valve disease (MVD). Methods Intra-operative epicardial mapping (interelectrode distance 2mm) of the right and left atrium (RA, LA), Bachmann’s Bundle (BB) and pulmonary vein area (PVA) was performed during SR in 67 patients (27 male, 67 ± 11 years) with or without a history of paroxysmal atrial fibrillation (PAF). Unipolar single potentials (SPs) were classified according to their differences in relative R- and S-wave amplitude ratios. Results Epicardial EGMs revealed a wide variation of R/S ratios. A clear predominance of S-waves was observed at BB and the RA in both the no history of AF (no AF) and PAF group (BB 88.8% vs. 85.9%, RA: 92.1% vs. 85.1%, respectively). Differences between both groups were found at the RA, BB and LA (P = 0.021, P = 0.003 and P = 0.013, respectively). EGM voltages of the RA, BB and PVA in the no AF group were significantly higher compared to the PAF group (P &amp;lt; 0.001, P &amp;lt; 0.001 and P &amp;lt; 0.001, respectively), and are mainly determined by the size of the S-waves amplitudes. Conclusions Though excitation of the atria during SR is heterogeneously disrupted in patients with MVD, a history of AF in this patient group is characterized by decreased SP amplitudes at BB due to loss of S-wave amplitudes. This, together with our findings that variation in EGM morphologies in our population is considerable, emphasizes the need for a diagnostic tool enabling identification of electropathology in the individual patient. Abstract Figure. Potential morphology distribution

Ultrasonic Spectrum Analysis of Granite Damage Evolution Based on Dry‐Coupled Ultrasonic Monitoring Technology

The self‐developed dry‐coupled rock ultrasonic monitoring system is adopted to set up a multidirectional and multiwaveform ultrasonic monitoring network, which aims to analyse the evolution law of acoustic spectrum parameters in the process of granite loading failure under uniaxial compression, to explore the dominant acoustic spectrum characteristic information at different stages of granite loading, and to verify in situ the damage monitoring of time‐effect deformation. The results show that the wave velocity, amplitude, and amplitude‐frequency of the first wave and the velocity of P‐wave and S‐wave show a significant upward trend in the rock compaction section. After entering the elastic stage, the three spectral parameters become peacefully stable, and the stage transformation is obvious. In the stable crack growth stage, with the initiation of the crack, the dominant frequency of S‐wave shows a significant stage transition compared with the global ultrasonic wave velocity and the first arrived amplitude, and the dominant frequency decreases by 6%. In the unstable crack growth stage, the three acoustic spectrum parameters present obvious downward trend, and the first arrived wave amplitude of S‐wave is found to have a significant decline of 39.1%. On the eve of failure, the amplitude‐frequency of S‐wave shows different feature from the P‐wave; that is, S‐wave transfers from the state of multipeak in wide frequency to the state of single peak in low frequency, which is the failure precursor of the rock sample.

Ultrasonic wave propagation characteristics for typical anisotropic failure modes of shale under uniaxial compression and real-time ultrasonic experiments

AbstractUniaxial loading and real-time ultrasonic experiments on shales were conducted to study the progressive failure of shale and the ultrasonic propagation characteristics during loading. The results show that the variations in P-wave and S-wave velocities with stress correspond to the crack damage process for the typical anisotropic failure of shale, and that the S-wave amplitude is sensitive to the damage that arises in shale during loading. If the bedding participates relatively simply in the failure (0° and 60° inclinations), the spectrum and the main frequency shape are simple and remain basically unchanged during loading. In the cases where the failure mode is complicated by the participation of the bedding and the matrix (30° and 90° inclinations), the spectrum and the main frequency shape are complex and change dynamically with loading. These results indicate that ultrasonic dynamic parameters reflect the differences in the failure of shale.

The V1-V3 transition index as a novel electrocardiographic criterion for differentiating left from right ventricular outflow tract ventricular arrhythmias.

The aim of this study was to develop a new electrocardiographic criterion for differentiating the origin of outflow tract ventricular arrhythmias (OT-VAs) with precordial transition in lead V3. A total of 147 consecutive patients with OT-VAs displaying precordial transition in lead V3 who underwent successful catheter ablation in the right ventricular outflow tract (RVOT) (n = 118) or left ventricular outflow tract (LVOT) (n = 29) were included in this study. The V1-V3 transition index was defined as the sum of S-wave amplitude in lead V1 and V2 during premature ventricular contractions (PVCs) divided by the S-wave amplitude during sinus rhythm (SR), respectively, minus the sum of R-wave amplitude in lead V1, V2, and V3 during PVCs divided by the R-wave amplitude during SR, respectively, i.e., [(SPVC/SSR)V1 + (SPVC/SSR)V2] - [(RPVC/RSR) V1 + (RPVC/RSR)V2 + (RPVC/RSR)V3]. The V1-V3 transition index was significantly higher for RVOT origins than for LVOT origins (1.25 ± 2.48 vs. - 3.94 ± 3.11; P < 0.001). Receiver operating characteristic (ROC) analysis revealed an area under the curve (AUC) of 0.931 for the V1-V3 transition index, and a cutoff value of > - 1.60 predicted a RVOT origin with a 93% sensitivity and 86% specificity. With respect to AUC and accuracy, the V1-V3 transition index was superior to any previously proposed ECG indices for differentiating left from right OT-VAs. In 37 prospective cases, the new index was able to predict the site of a RVOT origin with 95% accuracy (35 of 37 cases). The V1-V3 transition index is a useful novel ECG criterion for distinguishing left from right OT-VAs with precordial transition in lead V3.

Quark-Mass Dependence of Elastic πK Scattering from QCD.

We present a determination of the isospin-1/2 elastic πK scattering amplitudes in S and P partial waves using lattice quantum chromodynamics. The amplitudes, constrained for a large number of real-valued energy points, are obtained as a function of light-quark mass, corresponding to four pion masses between 200 and 400MeV, at a single lattice spacing. Below the first inelastic threshold, the P-wave scattering amplitude is dominated by a single pole singularity that evolves from being a stable bound state at the highest quark mass into a narrow resonance that broadens as the pion and kaon masses are reduced. As in experiment, the S-wave amplitude does not exhibit an obviously resonant behavior, but instead shows a slow rise from threshold, which is not inconsistent with the presence of a κ/K_{0}^{⋆}(700)-like resonance at the considered quark masses. As has been found in analyses of experimental scattering data, simple analytic continuations into the complex energy plane of precisely determined lattice QCD amplitudes on the real energy axis are not sufficient to model-independently determine the existence and properties of this state. The spectra and amplitudes we present will serve as an input for increasingly elaborate amplitude analysis techniques that implement more of the analytic structure expected at complex energies.

Flow-induced alterations of ultrasonic signatures and fracture aperture under constant state of stress in a single-fractured rock

Fluid-fracture surface interaction, caused by different mechanisms, is one of the underlying reasons for permeability reduction over long period of time in different georesources, such as deep geothermal systems and shale gas/oil reservoirs. The sensitivity of the ultrasonic signatures (e.g., frequency content, velocity, amplitude, and attenuation) to the changes in fracture aperture caused by fluid-fracture surface interactions can be considered as a probe for flow-induced fracture aperture evolution. Flow-through tests on an artificially fractured phyllite specimen from a geothermal reservoir along with the concurrent measurements of ultrasonic signatures of P- and cross-polarized S-waves demonstrated the sensitivity of ultrasonic signatures to the evolution of fracture aperture/permeability under a constant state of stress (i.e., constant pore and confining pressures). In particular, the closure of the fracture and the decrease of permeability led to an increase of the P-wave velocity, a decrease of the P-wave attenuation, and an increase of the S-wave amplitude. In addition, time evolution of the time-frequency maps of the transmitted ultrasonic waves revealed that partitioning of the frequency content slightly changes because the fracture aperture/permeability is altered. Specifically, alterations in hydraulic aperture are reflected in the changes of time-frequency partitioning, whereas under constant hydraulic aperture, the time-frequency partitioning is unaltered.

S -wave baryon nonleptonic decay amplitude in large−Nc chiral perturbation theory

The s-wave decay amplitude in the nonleptonic decay of baryons is analyzed within heavy baryon chiral perturbation theory in the large-N_c limit at one-loop order, where N_c is the number of color charges. Loop graphs with octet and decuplet intermediate states are systematically incorporated into the analysis and the effects of the decuplet-octet mass difference are accounted for. There are large-N_c cancellations between different one-loop graphs as a consequence of the large-N_c spin-flavor symmetry of QCD baryons. The predictions of large-N_c baryon chiral perturbation theory are in very good agreement both with the expectations from the 1/N_c expansion and with the experimental data.

Study of the quasi-two-body decays B^{0}_{s} rightarrow psi (3770) (psi (3686))pi ^+pi ^- with perturbative QCD approach

In this note, we study the contributions from the S-wave resonances, f_{0}(980) and f_{0}(1500), to the B^{0}_{s}rightarrow psi (3770)pi ^ {+}pi ^{-} decay by introducing the S-wave pi pi distribution amplitudes within the framework of perturbative QCD approach. Both the resonant and the non-resonant contributions are contained in the scalar form factor in the S-wave distribution amplitude Phi ^S_{pi pi }. Since the vector charmonium meson psi (3770) is a S–D wave mixed state, we calculate the branching ratios of S-wave and D-wave, respectively, and the results indicate that f_{0}(980) is the main contribution of the considered decay, and the branching ratio of the psi (2S) mode is in good agreement with the experimental data. We also take the S–D mixed effect into the B^{0}_{s}rightarrow psi (3686)pi ^ {+}pi ^{-} decay. Our calculations show that the branching ratio of B^{0}_{s}rightarrow psi (3770)(psi (3686))pi ^ {+}pi ^{-} can be at the order of 10^{-5}, which can be tested by the running LHCb experiments.

Investigation of site amplification factors for S- and P-waves from spectral inversions in the Tokyo metropolitan area, Japan—for application to earthquake early warnings

We performed spectral inversions using ground motion data observed by K-NET, KiK-net, SK-net, and the earthquake observation network of the East Japan Railway Company in the Tokyo metropolitan area, Japan, to evaluate the effects of site amplification factors of both S- and P-waves for the future use of an on-site earthquake early warning system based on predicted S-wave amplitudes from observed P-wave amplitudes. The source and path effects from the inversions were similar to those estimated by previous studies. The spatial distributions of the site amplification factors of the S- and P-waves depend on the geological conditions, especially for the S-waves. The site amplification factors of the S- and P-waves nearly agree with those calculated with a 1D reverberation theory using existing velocity models from KiK-net. The site amplification ratios of the S-waves to the P-waves show a decrease in the amplitudes at frequencies greater than 2–5 Hz, especially on the plateaus and in the coastal areas covered with thick soft layers because the site amplification factors of the S-waves are small in this frequency range and those of the P-waves are nearly constant over the entire frequency range. Further, the remarkable peaks of the site amplification factors for the S-waves are preserved in the site amplification ratios of the S-waves to the P-waves at sites in the valleys and on the boundaries between the plateaus and the lowlands.

Determination of s- and p-wave I = 1/2 Kπ scattering amplitudes in Nf = 2 + 1 lattice QCD

The elastic I=1/2, s- and p-wave kaon-pion scattering amplitudes are calculated using a single ensemble of anisotropic lattice QCD gauge field configurations with Nf=2+1 flavors of dynamical Wilson-clover fermions at mπ=230 MeV. A large spatial extent of L=3.7 fm enables a good energy resolution while partial wave mixing due to the reduced symmetries of the finite volume is treated explicitly. The p-wave amplitude is well described by a Breit–Wigner shape with parameters mK⁎/mπ=3.808(18) and gK⁎KπBW=5.33(20) which are insensitive to the inclusion of d-wave mixing and variation of the s-wave parametrization. An effective range description of the near-threshold s-wave amplitude yields mπa0=−0.353(25).

The reliability of microseismic moment-tensor solutions: Surface versus borehole monitoring

Source mechanisms of microseismic events, resolved as moment-tensor solutions, usually are obtained using either surface monitoring arrays, which appear to obtain mechanisms with high shear components, or borehole arrays, which tend to constrain more variable mechanisms with higher tensile components; however, the corresponding reliability of the solutions remains unclear. Synthetic tests are therefore conducted to compare the reliability of moment-tensor solutions from surface and two- and three-well borehole arrays based purely on geometry. Moment-tensor inversion is carried out for synthetically generated amplitudes with added random noise, and the bias and variance in the solutions are calculated. For the surface array, all inversions are able to constrain reliable results (with negligible bias and low variance), whereas borehole geometries with two wells produce reliable results only when including P- and S-wave amplitudes recorded on three components in the inversion (as is usual). Surface array inversion results show less bias and variance in the results compared with borehole results, and the three-borehole geometry shows significantly lower biases and estimation variances than the two-borehole geometry, most likely due to a greater sampling of the focal sphere. These results may explain in part why downhole moment-tensor inversion studies tend to resolve more variable mechanisms than surface arrays. Nonetheless, as well as geometry, other influences (e.g., signal-to-noise ratio) will influence the reliability of the solutions in real settings and different amplitude strengths of pure shear or tensile mechanisms combined with different path lengths, and thus energy dissipation for borehole or surface acquisitions also may play a role. Nonetheless, tests such as those in this study are useful to help design appropriate monitoring geometries and/or understand possible sources of bias and uncertainty in moment-tensor interpretations.

Characterization of naturally fractured Arbuckle Group in the Wellington Field, Kansas, using S-wave amplitude variation with offset

S-wave amplitude variation with offset (AVO) analysis is sensitive to the presence of fractures and can provide a high-resolution seismic-based fracture characterization as compared with traditionally used traveltime-based methods. To determine viable attributes for estimation of properties such as spatial density and fluid fill of fractures, S-wave AVO modeling and analysis is carried out in the Wellington Field, Kansas, where 9C-2D seismic data have been acquired. Analysis is performed on the Ordovician fractured-carbonate interval called the Arbuckle Group, which is being considered for [Formula: see text] sequestration. AVO modeling of the Arbuckle interval indicates that differences in AVO intercepts of different S-wave polarizations can estimate S-wave anisotropy parameter [Formula: see text], which gives an estimate of fracture density. In addition, modeling suggests that AVO gradients of [Formula: see text] and [Formula: see text] waves can be used to derive a seismic attribute to discriminate fluid fill in fractures, provided good-quality S-wave gathers are available. The intercept anisotropy (IA) attribute obtained from AVO intercepts of S-waves provides fracture density estimates within the Arbuckle Group. These estimates are consistent with the field-wide, low-frequency observations from seismic velocities and spatially limited, high-frequency estimates obtained from drill cores and sonic and borehole-image logs. The IA attribute highlights possible high-permeability zones in the Upper and Lower Arbuckle suitable for [Formula: see text] injection. The Middle Arbuckle indicates low fracture density, potentially acting as a baffle to vertical flow and providing a seal for the Lower Arbuckle. The gradient anisotropy attribute obtained from the AVO gradient of S-waves suggests that most fractures in the Arbuckle are brine saturated. This attribute has a potential application in monitoring the movement of a [Formula: see text] plume in the Arbuckle Group when time-lapse data become available. These results demonstrate that S-wave AVO attributes can supplement the P-wave derived subsurface properties and significantly reduce uncertainties in subsurface fracture characterization.