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Seismic anisotropy imposes first‐order constraints on the strain history of crust and upper mantle rocks. In this study, we analyze the mantle seismic anisotropy of the Western Canada Sedimentary Basin using a new shear wave spitting data set consisting of 1,333 teleseismic arrivals from 82 seismic stations. The resulting 332 high‐quality measurements yield a regional mean apparent splitting time (i.e., the magnitude of anisotropy) of 1.1 ± 0.3 s and an average fast orientation (i.e., the direction of anisotropy) of 54.6° ± 17.2°, which favor a two‐layer anisotropic model based on the 90° back azimuthal periodicity in both parameters. The northeast trending fast orientations dominate the lower layer at lithospheric depths and are approximately parallel to the present‐day absolute plate motions (APMs; i.e., <35°) due to the active asthenospheric flow. On the other hand, deviations from the APMs along the Canadian Rocky Mountain foothills could reflect disrupted mantle flow surrounding a southwestward migrating cratonic lithosphere. Also revealed are two elongated upper‐layer anisotropic anomalies in the lithosphere that are spatially correlated with Moho depths. Their characteristics suggest frozen‐in anisotropy imprinted along two convergent boundaries: (1) the Paleoproterozoic Snowbird Tectonic Zone that separates northeast (north) from northwest (south) fast directions and (2) the foothills of the Rocky Mountains that exhibit northeast trending orientations consistent with those of the APMs, maximum crustal stress, and electromagnetic anisotropy. Compressions associated with the Cordilleran orogenesis could be responsible for the spatial changes in the shear wave anisotropy from the foothills to the cratonic interior. Key Points: New shear wave splitting results disclose layered anisotropy beneath the western LaurentiaDifferential splitting times from two‐layer anisotropic modeling are correlated with Moho depths, suggesting crustal impact on the shear wave splitting observations across AlbertaThe upper‐layer fossil anisotropic fabrics reveal two collision‐related convergent events that formed the western North America [ABSTRACT FROM AUTHOR]

Understanding the present-day fast seismic velocity anomalies in the mantle requires an accurate kinematic reconstruction of past convergent tectonics. Using the paleomagnetism-based absolute reconstruction method from Wu and Kravchinsky (2014), we present here the restoration of the closing of the Mongol-Okhotsk Ocean (MOO) that existed between Siberia and North China-Amuria (NCA) during the Mesozoic. Three stages, i.e., 250-200 Ma, 200-150 Ma, and 150-120 Ma, are identified from the time-varying convergence rates of Siberia and NCA. The spherical distance between the suture margins was reduced by approximately 66.7% at an average convergence rate of 8.8 ± 0.6 cm/yr during the first stage at 250-200 Ma, when approximately 62.5-76.1% of the slabs associated with the MOO lithosphere were formed primarily through intraoceanic convergence. In the second stage at 200-150 Ma, the spherical distance was reduced by another 21.1% with a convergence rate of 3.6 ± 0.3 cm/yr. During this stage, approximately 14.2-30.9% of the MOO slabs were formed and continental-oceanic convergence outpaced intraoceanic subduction. In the last stage at 150-120 Ma, the convergence rate dropped to approximately 0.4-0.6 cm/yr with the formation of approximately 4.6-9.8% slabs associated with the MOO lithosphere. The final closure of the remnant MOO basin could have been accomplished by 130-120 Ma, which explains the origin of the fast-velocity anomalies inside the restored continents at 120 Ma near the suture margins. [ABSTRACT FROM AUTHOR]

Knowledge of the mantle reflectivity structure is highly dependent on our ability to efficiently extract, and properly interpret, small seismic arrivals. Among the various data types and techniques, long-period SS/PP precursors and high-frequency receiver functions are routinely utilized to increase the confidence of the recovered mantle stratifications at distinct spatial scales. However, low resolution and a complex Fresnel zone are glaring weaknesses of SS precursors, while over-reliance on receiver distribution is a formidable challenge for the analysis of converted waves from oceanic regions. A promising high frequency alternative to receiver functions is P′P′ precursors, which are capable of resolving mantle structures at vertical and lateral resolution of ∼5 and ∼200 km, respectively, owing to their spectral content, shallow angle of incidence and near-symmetric Fresnel zones. This study presents a novel processing method for both SS (or PP) and P′P′ precursors based on deconvolution, stacking, Radon transform and depth migration. A suite of synthetic tests is performed to quantify the fidelity and stability of this method under different data conditions. Our multiresolution survey of the mantle at targeted areas near Nazca-South America subduction zone reveal both olivine and garnet related transitions at depths below 400 km. We attribute a depressed 660 to thermal variations, whereas compositional variations atop the upper-mantle transition zone are needed to explain the diminished or highly complex reflected/scattered signals from the 410 km discontinuity. We also observe prominent P′P′ reflections within the transition zone, and the anomalous amplitudes near the plate boundary zone indicate a sharp (∼10 km thick) transition that likely resonates with the frequency content of P′P′ precursors. The migration of SS precursors in this study shows no evidence of split 660 reflections, but potential majorite–ilmenite (590–640 km) and ilmenite–perovskite transitions (740–750 km) are identified based on similarly processed high-frequency P′P′ precursors. Additional findings of severely scattered energy in the lithosphere and distinct lower mantle reflections at ∼800 km could be potentially important but require further verifications. Overall, our improved imaging methods and the strong sensitivity of P′P′ precursors to the existence, depth, sharpness and strength of reflective structures offer significant future promise for the understanding of mantle mineralogy and dynamics. [ABSTRACT FROM AUTHOR]

SUMMARY Simultaneous estimation of origin time, location and moment tensor of seismic events is critical for automatic, continuous, real-time monitoring systems. Recent studies have shown that such systems can be implemented via waveform fitting methods based on pre-computed catalogues of Green's functions. However, limitations exist in the number and length of the recorded traces, and the size of the monitored volume that these methods can handle without compromising real-time response. This study presents numerical tests using a novel waveform fitting method based on compressive sensing, a field of applied mathematics that provides conditions for sampling and recovery of signals that admit a sparse representation under a known base or dictionary. Compressive sensing techniques enable us to determine source parameters in a compressed space, where the dimensions of the variables involved in the inversion are significantly reduced. Results using a hypothetical monitoring network with a dense number of recording stations show that a compressed catalogue of Green's functions with 0.004 per cent of its original size recovers the exact source parameters in more than 50 per cent of the tests. The gains in processing time in this case drop from an estimated 90 days to browse a solution in the uncompressed catalogue to 41.57 s to obtain an estimation using the compressed catalogue. For simultaneous events, the compressive sensing approach does not appear to influence the estimation results beyond the limitations presented by the uncompressed case. The main concern in the use of compressive sensing is detectability issues observed when the amount of compression is beyond a minimum value that is identifiable through numerical experiments. Tests using real data from the 2002 June 18 Caborn Indiana earthquake show that the presence of noise and inaccurate Green's functions require a smaller amount of compression to reproduce the solution obtained with the uncompressed catalogue. In this case, numerical simulation enables the assessment of the amount of compression that provides a reasonable rate of detectability. Overall, the numerical experiments demonstrate the effectiveness of our compressed domain inversion method in the real-time monitoring of seismic sources with dense networks of receivers. As an added benefit of the compression process, the size of the monitored volume can also be increased under specific restrictions while maintaining the real-time response. [ABSTRACT FROM AUTHOR]

SUMMARY Using a proper parametrization, the source displacement field of a seismic event can be efficiently reconstructed by a redundant dictionary of Green's functions based on sparse representation theory. Then, by subjecting the pre-existing event records and pre-computed dictionary of Green's functions into a sparsity-promoting algorithm, it is possible to simultaneously evaluate the origin time, hypocentre coordinates and seismic moment tensor. The proposed method is applicable to single- or multiple-source scenarios and, with minor adjustments, can be a valuable tool for real-time, automatic monitoring systems. This study demonstrates the effectiveness and accuracy of the dictionary-based approach via (1) detection of microseismic events produced during the hydraulic fracturing of oil and gas wells and (2) inversion of a small-magnitude, regional earthquake (2002 June 18 in Caborn, Indiana) data. Our experiments based on numerical simulations and earthquake observations underscore the largely untapped potential of dictionary-based approaches and sparse representation theory in continuous source parameter recovery. [ABSTRACT FROM AUTHOR]

Moment tensor inversion techniques are widely used in global and regional seismic applications. When the ray-path trajectories are confined in a single plane (e.g., in isotropic media using a vertical array of receivers or an array that deviates from the vertical in the direction of wave propagation) only five out of six elements of the moment tensor are resolvable. This study investigates the resolvability of the complete seismic moment tensor for single-well monitoring geometries. By analyzing the resolution matrix, we demonstrate that a correct representation of the five resolvable elements of the moment tensor is only possible in a local reference system. For a vertical array of receivers, a suitable choice of condition number can assist the acquisition design. For a non-vertical array, our numerical modeling experiments suggest that the required distance and orientation of receivers for a full moment tensor inversion can be satisfied in a deviated well. In this case, information embedded in the condition number is valuable for determining the required distribution of receivers along the well. [ABSTRACT FROM AUTHOR]

In this paper, we present a new approach to estimate high-resolution teleseismic receiver functions using a simultaneous iterative time-domain sparse deconvolution. This technique improves the deconvolution by using reweighting strategies based on a Cauchy criterion. The resulting sparse receiver functions enhance the primary converted phases and its multiples. To test its functionality and reliability, we applied this approach to synthetic experiments and to seismic data recorded at station ABU, in Japan. Our results show Ps conversions at approximately 4.0 s after the primary P onset, which are consistent with other seismological studies in this area. We demonstrate that the sparse deconvolution is a simple, efficient technique in computing receiver functions with significantly greater resolution than conventional approaches. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the shear velocity structure under the northern East Pacific Rise at the latitude range of 9–18°N, using intermediate-period Rayleigh and Love waves. The selected ocean-bottom seismic records provide source–receiver paths that ideally constrain the lithospheric mantle structure beneath the southern Rivera plate and the Mathematician paleoplate. The Rayleigh wave data infer a relatively thin (∼30 km) lithosphere under the eastern side of the present-day East Pacific Rise. The associated shear velocities are consistent with existing models of oceanic mantle beneath this region, and the estimated plate age of 2–3 million years agrees with results from magnetic dating. The west of the rise axis is characterized by a thicker and faster lithosphere than the eastern flank, and such structural differences suggest the presence of a relatively old Mathematician paleoplate. The discontinuous change in mantle structure across the East Pacific Rise spreading center are observed in both isotropic and anisotropic velocities. The young oceanic lithosphere east of the rise axis shows strong polarization anisotropy, where the dominant orientation of crystallographic axes roughly parallels the spreading direction. However, the western flank of the rise axis is approximately isotropic, and the lack of anisotropy suggests complex deformation mechanisms associated with earlier episodes of ridge segmentation, propagation and dual-spreading on and around the Mathematician paleoplate. [Copyright &y& Elsevier]

Until now, modelling of threee-dimensional (3-D) velocity variations in the mantle and topography of the transition zone discontinuities have been considered separately. Velocity models were obtained assuming that the radii of the discontinuities are constant. Then, the travel time data sensitive to the topography, such as the SS precursors, were corrected for the effect of 3-D seismic structure and interted for depth variations of a discontinuity. Such a procedure is unsatisfactory, as it may introduce artefacts that could significantly affect the topographic results; the opposite trade-off is less likely to introduce conceptually important changes in the velocity distribution but should also be considered. In this study we bring together the same set of S-velocity sensitive sata as used by Gu st al. and combine it with a large set of differential travel times of SS-S400S, S-S670S, and direct measurements of S400S-S670S. We formulate the inverse problem in terms of the volumetric (3-D) and topographic (2-D) perturbations for both the 400- and 670-km discontinuities. The best-fitting model of the joint inversion significanlty improves the variance reduction of SS-S400S and SS-S670S residuals. The velocity distribution in the resulting model, TOPOS362D1, is very similar to that in model S362D1 (with correlation coefficients >0.9 throughout the mantle), which indicates that lateral variations of discontinuity depths have only minor influence on global modelling of velocity. Important changes, however, have been made to the topography of 400- and 670-km discontinuities with respect to those obtained earlier assuming an existing velocity model. The overall undulation of the 400-km discontinuity is considerably less than that reported by earlier global studies; in TOPOS362D1 its maximum variation does not exceed 12 km. The strong degree-1 component before the joint inversion has decreased, such that the coreelation between the velocities above the discontinuity... [ABSTRACT FROM AUTHOR]

Examines results of a joint inversion for compressional and shear velocity in the mantle using a data set consisting of travel times, wave forms and surface wave dispersion measurements. Peak variations in the model; Ratio of velocity perturbations; Correlation between bulk-sound and shear velocity.

The Pacific large low-shear-velocity province (LLSVP), as revealed by cluster analysis of global tomographic models, hosts multiple internal anomalies, including a notable gap (~20° wide) between the central and eastern Pacific. The cause of the structural gap remains unconstrained. Directly above this structural gap, we identify an anomalously thick mantle transition zone east of the East Pacific Rise, the fastest-spreading ocean ridge in the world, using a dense set of SS precursors. The area of the thickened transition zone exhibits faster-than-average velocities according to recent tomographic images, suggesting perturbed postolivine phase boundaries shifting in response to lowered temperatures. We attribute this observation to episodes of Mesozoic-aged (250 to 120 million years ago) intraoceanic subduction beneath the present-day Nazca Plate. The eastern portion of the Pacific LLSVP was separated by downwelling because of this ancient oceanic slab. Our discovery provides a unique perspective on linking deep Earth structures with surface subduction. [ABSTRACT FROM AUTHOR]

This study uses seismological principles and techniques including waveform simulations and travel time calculations to reveal the nature of ultrasound wave propagation in long bones at small offsets (source-to-receiver distances) and times. Our experiments confirm the existence of reflected and converted body waves originating from wave interaction at the internal interfaces of a bone structure. We demonstrate that the bone ultrasound responses can be successfully simulated and properly interpreted based on a simple, horizontally layered approximation. [ABSTRACT FROM AUTHOR]

The Pacific large low-shear-velocity province (LLSVP), as revealed by cluster analysis of global tomographic models, hosts multiple internal anomalies, including a notable gap (~20° wide) between the central and eastern Pacific. The cause of the structural gap remains unconstrained. Directly above this structural gap, we identify an anomalously thick mantle transition zone east of the East Pacific Rise, the fastest-spreading ocean ridge in the world, using a dense set of SS precursors. The area of the thickened transition zone exhibits faster-than-average velocities according to recent tomographic images, suggesting perturbed postolivine phase boundaries shifting in response to lowered temperatures. We attribute this observation to episodes of Mesozoic-aged (250 to 120 million years ago) intraoceanic subduction beneath the present-day Nazca Plate. The eastern portion of the Pacific LLSVP was separated by downwelling because of this ancient oceanic slab. Our discovery provides a unique perspective on linking deep Earth structures with surface subduction.

Background: Obesity, a common metabolic disease, is a known cause of male infertility due to its associated health risk. Long noncoding RNAs (lncRNAs) have also been reported to be associated with male reproductive diseases; however, their role in the association between high-fat diet-induced obesity (DIO) and male reproduction remains unclear., Methods: We used microarray analysis to compare the expression levels of lncRNAs and mRNAs in the spermatozoa of rats with DIO and normal rats. We selected a few lncRNAs that were obviously up-regulated or down-regulated, and then used RT-PCR to verify the accuracy of their expression. We then performed a functional enrichment analysis of the differentially expressed mRNAs using gene ontology and pathway analysis. Finally, target gene predictive analysis was used to explore the relationship between lncRNAs and mRNAs., Results: The results revealed a statistically significant difference in the fasting blood glucose level in rats with DIO and control rats. We found that 973 lncRNAs and 2,994 mRNAs were differentially expressed in the sperm samples of the DIO rats, compared to the controls. GO enrichment analysis revealed 263 biological process terms, 39 cellular component terms, and 40 molecular function terms ( p  < 0.01) in the differentially expressed mRNAs. The pathway analysis showed that metabolic pathways were most enriched in protein-coding genes., Discussion: To the best of our knowledge, this is the first report to show differences in the expression levels of lncRNAs and mRNAs in the sperms of rats with DIO and normal rats, and to determine the expression profile of lncRNAs in the sperm of rats with DIO. Our results have revealed a number of lncRNAs and pathways associated with obesity-induced infertility, including metabolic pathways. These pathways could be new candidates that help cope with and investigate the mechanisms behind the progression of obesity-induced male infertility., Competing Interests: The authors declare there are no competing interests.