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The joint inversion of Rayleigh and Love waves plays a crucial role in mitigating the non‐uniqueness of surface wave inversion results and enhancing the stability of these inversions. Existing approaches to the joint inversion of Rayleigh and Love wave dispersion curves, which rely on conventional objective functions, often struggle with complex stratigraphic configurations and yield results of limited accuracy. This study introduces two novel nonlinear joint inversion techniques for Rayleigh and Love waves: Pearson correlation coefficient and thickness mean sharing. The Pearson correlation coefficient approach employs the Pearson correlation coefficient and alternating iterative objective functions to synchronize the shear wave velocity structures derived from Rayleigh and Love waves, thereby enhancing the accuracy of the joint inversion. Conversely, the thickness mean sharing method computes an average of the thickness values obtained in each iteration of the inversion, utilizing the traditional joint inversion objective function. Tests on three distinct stratigraphic structures—characterized by increasing velocity, high‐speed hard interlayers and low‐speed soft interlayers—as well as on measured data, demonstrate that the proposed methods significantly improve the stability and accuracy of nonlinear joint inversion. [ABSTRACT FROM AUTHOR]

The Pannonian Basin, situated in Central Europe, is surrounded by the Alpine, Carpathian and Dinaric orogens. To understand its tectonic characteristics and evolution, we determine a shear wave velocity model of its crust, mantle lithosphere and asthenosphere consistently by jointly inverting Rayleigh wave phase velocities measured consistently from earthquake (EQ) and ambient noise (AN) data. For the AN data, continuous waveform data were collected from 1254 stations, covering an area within 9° from the centre of the Pannonian Basin during the time period from 2006 to 2018. This data set enabled the extraction of over 164 464 interstation Rayleigh phase-velocity curves, after applying a strict quality control workflow. For the EQ data set more than 2000 seismic events and about 1350 seismic stations were used in the broader Central and Eastern European region between the time-span of 1990 to 2015, allowing us to extract 139 987 quality controlled Rayleigh wave phase-velocity curve. Using the combined data set, a small period- and distance-dependent bias between ambient noise and earthquake measurements, mostly below 1 per cent but becoming larger towards longer periods has been found. After applying a period and distance dependent correction, we generated phase-velocity maps, spanning periods from 5 to 250 s. 33 981 local dispersion curves were extracted and a new approach is introduced to link their period-dependent roughness to the standard deviation. Using a non-linear stochastic particle swarm optimization, a consistent 3-D shear wave velocity model (PanREA2023) encompassing the crust and upper mantle down to 300 km depth was obtained with a lateral resolution reaching about 50 km at the centre of the study area for shorter periods. The crust beneath the Carpathian orogen exhibits a distinct low-velocity anomaly extending down to the Moho. It is referred to as Peri-Carpathian anomaly. Similar anomalies were observed in the Northern Apennines, while the Eastern Alps and Dinarides, as collisional orogens, generally demonstrate higher velocities in the upper crust. High crustal shear wave velocities are also evident in the Bohemian Massif and the East European Craton. The brittle upper crust of the Pannonian Basin is characterized by alternating NE–SW trending high- and low-velocity anomalies: the western and central Pannonian low-velocity anomalies and the Transdanubian and Apuseni high-velocity anomalies related to Miocene sedimentary basins and intervening intervening interbasinal highs exposing Pre-Cenozoic rocks including crystalline basement rocks. Beneath the Southeastern Carpathians, a NE-dipping slab was identified, extending to depths of at least 200 km, while a slab gap is evident beneath the Western Carpathians. A short south-dipping Eurasian slab was imaged beneath the Eastern Alps down to only 150–200 km depth. The Adriatic lithosphere is subducting near-vertically dipping beneath the Northern Apennines, and a slab gap was observed beneath the Central Apennines. In the Northern Dinarides, a short slab was evident, reaching depths of around 150 km. The Southern Dinarides featured a thinned but possibly incompletely detached slab. [ABSTRACT FROM AUTHOR]

Over the past decades, surface wave methods have been routinely employed to retrieve the physical characteristics of the first tens of meters of the subsurface, particularly the shear wave velocity profiles. Traditional methods rely on the application of the multichannel analysis of surface waves to invert the fundamental and higher modes of Rayleigh waves. However, the limitations affecting this approach, such as the 1D model assumption and the high degree of subjectivity when extracting the dispersion curve, motivate us to apply the elastic full‐waveform inversion, which, despite its higher computational cost, enables leveraging the complete information embedded in the recorded seismograms. Standard approaches solve the full‐waveform inversion using gradient‐based algorithms minimizing an error function, commonly measuring the misfit between observed and predicted waveforms. However, these deterministic approaches lack proper uncertainty quantification and are susceptible to get trapped in some local minima of the error function. An alternative lies in a probabilistic framework, but, in this case, we need to deal with the huge computational effort characterizing the Bayesian approach when applied to non‐linear problems associated with expensive forward modelling and large model spaces. In this work, we present a gradient‐based Markov chain Monte Carlo full‐waveform inversion where we accelerate the sampling of the posterior distribution by compressing data and model spaces through the discrete cosine transform. Additionally, a proposal is defined as a local, Gaussian approximation of the target density, constructed using the local Hessian and gradient information of the log posterior. We first validate our method through a synthetic test where the velocity model features lateral and vertical velocity variations. Then we invert a real dataset from the InterPACIFIC project. The obtained results prove the efficiency of our proposed algorithm, which demonstrates to be robust against cycle‐skipping issues and able to provide reasonable uncertainty evaluations with an affordable computational cost. [ABSTRACT FROM AUTHOR]

Ambient seismic noise has proven to be a particularly effective tool for subsurface imaging in the last decades, with applications ranging from near surface imaging, to crustal or upper mantle tomography. Fundamentally, it relies on the cross correlations of continuous recordings of ground motion data at pairs of seismic stations. Processing steps have become more refined and promising in extracting meaningful signals that can further be used in a range of classic seismology tools. The processing, however, is usually cumbersome, time- and memory-consuming, as it requires years of continuous noise recorded at broadband seismic stations, to obtain high signal-to-noise ratio empirical Green's functions. In order to ease the research effort, we built a database of ambient seismic noise cross correlations between pairs of broadband seismic stations that operated in Central and Eastern Europe between 1999 and 2020. The database is part of the Eastern European Ambient Seismic Noise (EENSANE) research project hosted by the National Institute of Earth Physics in Romania and will progressively grow as more stations become available, such as those provided by the new AdriaArray network. Based on this database and using state-of-the-art inversion techniques, we developed a series of near-surface and crustal tomography models of the Eastern European craton, the Trans-European Suture Zone and younger accreted terranes from Central Europe. Our integrated models provide both isotropic and azimuthally anisotropic seismic velocities from surface wave dispersion and attenuation parameters from the decay envelopes of Rayleigh waves. Using horizontal-to-vertical ratios of ambient noise, we also recovered the fundamental frequency of resonance and near surface shear wave velocity models beneath stations located across the Carpathian Orogen. Based on cross-correlation functions, we were also able to retrieve the seismic wavefield and peak ground displacement amplitudes from past earthquakes decades after their occurrence, offering a chance for improving seismic hazard and risk models in seismically vulnerable and developing regions of Europe. Our multidisciplinary results prove the versatility of ambient noise uses and the importance of the EENSANE database for a wide range of seismological imaging and hazard applications. [ABSTRACT FROM AUTHOR]

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We construct the 3D Shear wave velocity and azimuthal anisotropy images in the southern Chuandian block using phase velocity dispersion of Rayleigh wave in the period of 5–45 s. The images show two extensive low-velocity zones with a depth range of 20–40 km. The west range of the low-velocity extends from the Lijiang-Xiaojinhe fault to the Red River fault, while its east range follows along the Xiaojiang fault. Two ranges of low velocities are merged at the southern inner belt of the Emeishan Large Igneous Provinces (ELIP). The observed fast directions of azimuthal anisotropy are consistent with the extension of low-velocity ranges at the lower crust. The findings reveal the presence of two potential weak channels in the lower crust, characterized by low-velocity zones, which align with the hypothesis of lower crustal flow. Meanwhile, the crust around the inner belt of ELIP exhibits a high-velocity body characterized by a northeast-trending and counter-clockwise azimuthal anisotropy. Combined with geological data, we attribute the high S-velocity to a mafic–ultramafic magma reservoir of the ELIP, which blocks the continuity of crustal flow within the southern Chuandian block, thus dividing the lower crustal flow into two branches. Additionally, we also find the fast directions of azimuthal anisotropy above 20 km align well with the strike-slip fault orientations. The above research results indicate that the crustal deformation in the southern Chuandian block is likely attributed to the joint action of the two deformation mechanisms. One involves a lower crustal flow model, while the other entails rigid extrusion controlled by the deep-seated, large-scale strike-slip faults in the upper crust. [ABSTRACT FROM AUTHOR]

Various engineering equipments and devices use elastic vibrations and acoustic waves extensively for non-destructive testing and technical diagnostics of various materials and products. The propagation characteristics of plane and Rayleigh-type surface waves in an incompressible transversely isotropic diffusive material are investigated in context of nonlocal elasticity theory. The governing equations of motion for the medium are specialized in a plane and solved for time-harmonic solutions. A velocity equation for homogeneous plane wave is obtained which indicates the existence of two plane transverse waves. The two-dimensional equations are also solved for surface wave solutions and a Rayleigh characteristic equation is obtained. A numerical example is taken to illustrate graphically the effects of nonlocality, diffusion and material anisotropy parameters on the speeds of plane and Rayleigh surface waves. [ABSTRACT FROM AUTHOR]

This study investigated the sensitivity and specificity of identifying heart failure with reduced ejection fraction (HFrEF) from measurements of the intensity and timing of arterial pulse waves. Previously validated methods combining ultrafast B-mode ultrasound, plane-wave transmission, singular value decomposition (SVD), and speckle tracking were used to characterize the compression and decompression ("S" and "D") waves occurring in early and late systole, respectively, in the carotid arteries of outpatients with left ventricular ejection fraction (LVEF) < 40%, determined by echocardiography, and signs and symptoms of heart failure, or with LVEF ≥ 50% and no signs or symptoms of heart failure. On average, the HFrEF group had significantly reduced S-wave intensity and energy, a greater interval between the R wave of the ECG and the S wave, a reduced interval between the S and D waves, and an increase in the S-wave shift (SWS), a novel metric that characterizes the shift in timing of the S wave away from the R wave of the ECG and toward the D wave (all P < 0.01). Receiver operating characteristics (ROCs) were used to quantify for the first time how well wave metrics classified individual participants. S-wave intensity and energy gave areas under the ROC of 0.76–0.83, the ECG-S-wave interval gave 0.85–0.88, and the S-wave shift gave 0.88–0.92. Hence the methods, which are simple to use and do not require complex interpretation, provide sensitive and specific identification of HFrEF. If similar results were obtained in primary care, they could form the basis of techniques for heart failure screening. NEW & NOTEWORTHY: We show that heart failure with reduced ejection fraction can be detected with excellent sensitivity and specificity in individual patients by using B-mode ultrasound to detect altered pulse wave intensity and timing in the carotid artery. [ABSTRACT FROM AUTHOR]

Adequate estimation of S-wave velocity (Vs) structure is a significant parameter in the seismic micro zonation studies. To this purpose, different techniques, such as down-hole measurements and inversion of surface wave's dispersion curves are proposed for modeling VS profile. In the last decade, modeling Vs profile from the Rayleigh wave's ellipticity curve (H/V) is more applicable owing to its rapid and simple data gathering procedure. However, regarding the ambiguities in the inversion of H/V curves, obtaining the reliable results priori information, such as down-hole measurement, to constrain the final Vs model is vital. This study addressed this challenge, and based on a hybrid artificial intelligence method introduced a new technique to invert the Rayleigh wave ellipticity curve with acceptable performance. To do that, first model parameters (i.e. number of layers and corresponding thicknesses and shear wave velocities) by the ensemble of neural networks (ENN) were predicted, and then further inversion by jellyfish searching (JS) algorithm (named ENN-JS inversion method) was carried out to obtain a more reasonable Vs model. To build the ensemble system, ten base networks were arranged. To train the neural networks, synthetic Rayleigh wave ellipticity data by forward modeling approach were generated. The combination of the outputs of based networks was performed using the averaging method. Then, JS inversion algorithm was applied to estimate the final adequate Vs model. ENNs provide essential information to the JS searching algorithm on the number of layers and proper search spaces for model parameters. Synthetic and actual datasets tested the ENN-JS inversion technique. Findings show the proposed method provides a robust method for the inversion of Rayleigh wave ellipticity data. [ABSTRACT FROM AUTHOR]

The nondestructive spectral analysis of surface waves (SASW) technique determines the shear wave velocities along the wide wavelength range using Rayleigh-type surface waves that propagate along pairs of receivers on the surface. The typical configuration of source-receivers consists of a vertical source and three vertical receivers arranged in a linear array. While this approach allows for effective site characterization, laterally variable sites are often challenging to characterize. In addition, in a traditional SASW test configuration system, where sources are placed in one direction, the data are collected more on one side, which can cause an imbalance in the interpretation of the data. Data interpretation issues can be resolved by moving the source to opposite ends of the original array and relocating receivers to perform a second complete set of tests. Consequently, two different Vs profiles can be provided with only a small amount of additional time at sites where lateral variability exists. Furthermore, the testing procedure can be modified to enhance the site characterization during data collection. The advantages of performing SASW testing in both directions are discussed using a real case study. [ABSTRACT FROM AUTHOR]

We computed a 3-D shear wave velocity model of the Marmara Sea region from ambient noise tomography. The correlations of up to 8 yr of vertical-component seismic recordings from 80 broad-band stations provided Rayleigh wave group velocity measurements in the period band 6–21 s at more than 1400 selected virtual source–receiver pairs. Rayleigh wave group velocity maps were used to derive a shear wave velocity model through simulated annealing inversion. The resulting crustal model provides coverage of the Marmara Sea along with its surrounding regional tectonic features. This allows for an investigation of the spatial extents of the Marmara Sea on a scale larger than that of basins. The low-velocity structures of the Marmara Sea and the Thrace Basins are coeval to a depth of approximately 9 km. The crustal velocities beneath the Marmara Sea basins exhibit a low vertical gradient and smooth horizontal variations. The regional tectonic structures, such as Istranca Massif, Istanbul and Sakarya Zones, display sharp velocity contrasts with the lower velocity crust beneath the Marmara Sea. The observed low crustal velocities, along with depth variations of the velocity isosurfaces (i.e. 3.4 km s−1) indicate that the Marmara region is a structural depression much deeper and larger than the three basins of the North Marmara Trough. The North Anatolian Fault Zone is unlikely to be the primary factor contributing to the origin of this significant depression, as the basin's development appears to have occurred before the fault propagated into the region. [ABSTRACT FROM AUTHOR]

Borneo and Sulawesi are two large islands separated by the Makassar Strait that lie within the complex tectonic setting of central Indonesia. The seismic structure beneath this region is poorly understood due to the limited data availability. In this study, we present Rayleigh wave tomography results that illuminate the underlying crustal structure. Group velocity is retrieved from dispersion analysis of Rayleigh waves extracted from the ambient noise field by cross-correlating long-term recordings from 108 seismic stations over a period of 8 months. We then produce a 3-D shear wave velocity model via a two-stage process in which group velocity maps are computed across a range of periods and then sampled over a dense grid of points to produce pseudo-dispersion curves; these dispersion curves are then separately inverted for 1-D shear wave velocity (Vs), with the resultant models combined and interpolated to form a 3-D model. In this model, we observed up to ± 1.2 km s−1 lateral Vs heterogeneities as a function of depth. Our models illuminate a strong low shear wave velocity (Vs) anomaly at shallow depth (≤ 14 km) and a strong high Vs anomaly at depths of 20–30 km beneath the North Makassar Strait. We inferred the sediment basement and Moho depth from our 3-D Vs model based on iso-velocity constrained by the positive vertical gradient of the Vs models. The broad and deep sedimentary basement at ∼14 ± 2 km depth beneath the North Makassar Strait is floored by a shallow Moho at ∼22 ± 2 km depth, which is the thinnest crust in the study area. To the east of this region, our model reveals a Moho depth of ∼45 ± 2 km beneath Central Sulawesi, the thickest crust in our study area, which suggests crustal thickening since the late Oligocene. Moreover, the presence of high near-surface Vs anomalies with only slight changes of velocity with increasing depth in southwest Borneo close to Schwaner Mountain confirm the existence of a crustal root beneath this region. [ABSTRACT FROM AUTHOR]

We investigate the self-modulation of Love waves propagating in a nonlinear half-space covered by a nonlinear layer. We assume that the constituent material of the layer is nonlinear, homogeneous, isotropic, compressible, and hyperelastic, whereas for the half-space, it is nonlinear, heterogeneous, compressible and a different hyperelastic material. By employing the nonlinear thin layer approximation, the problem of wave propagation in a layered half-space is reduced to the one for a nonlinear heterogeneous half-space with a modified nonlinear homogeneous boundary condition on the top surface. This new problem is analyzed by a relevant perturbation method, and a nonlinear Schrödinger (NLS) equation defining the self-modulation of waves asymptotically is obtained. The dispersion relation is derived for different heterogeneous properties of the half-space and the thin layer. Then the results of the thin layer approximation are compared with the ones for the finite layer obtained in Teymur et al. (Int J Eng Sci 85:150–162, 2014). The solitary solutions of the derived NLS equation are obtained for selected real material models. It has been discussed how these solutions are influenced by the heterogeneity of the semi-infinite space. [ABSTRACT FROM AUTHOR]

The seismological data recorded at our four semi-permanent broadband seismographs installed by the CSIR-NGRI, Hyderabad, Telangana in the Aravalli mobile belt (AMB) and Rajasthan craton in the northwest Indian shield during the period 2014–2016 are used in the study. The 16 selected regional Indian earthquakes of Mw 5.5–7.8 that occurred in the North India region recorded at the four seismic stations are used to compute the surface wave (both Rayleigh and Love waves) group velocity dispersion characteristics and average 1-D regional shear wave velocity (Vs) structure beneath the North India which covers the northern part of India between the whole Himalayan region and Rajasthan craton including AMB. First, we compute Rayleigh waves (at 7–87 s) dispersion curves and Love waves (at 7–82 s) group velocity dispersion curves by utilizing the standard frequency time analysis (FTAN) of 3-component broadband data recorded at these four 3-component broadband seismic stations. After that, using the logarithmic stacking technique, we compute the final average stacked fundamental mode dispersion curves of surface waves (both Love and Rayleigh waves) for our study area. Then, we finally invert the final average dispersion curves of surface waves (both Love and Rayleigh waves) to compute the average one-dimensional regional shear velocity structure beneath North India. Our modelling result in North India suggests a two-layered crustal structure with a crustal thickness of 39 km. The thickness of the first crustal layer (upper crust) is 20 km with a shear wave velocity (Vs) of 3.30 km/s. On the other hand, the second crustal layer (lower crust) marks a 19-km thickness with a Vs of 3.70 km/s. Our modelling result suggests that the Vs of the upper mantle is found to be 4.35 km/s below the study region. Research highlights: Modelled average one-dimensional regional Vs structure below northern part of India. A 2-layered crustal velocity model below North India. Upper crust at 20 km thick with Vs of 3.30 km/s. And, lower crust at 19 km thick with Vs of 3.70 km/s. The Moho depth is 39 km and Vs below the Moho depth is found to be 4.35 km. [ABSTRACT FROM AUTHOR]

In this study we recast surface wave traveltime tomography as an inverse problem constrained by an eikonal equation and solve it using the efficient adjoint‐state method. Specifically, recognizing that large topographic variations and high surface wave frequencies can make the topographic effect too significant to ignore, we employ an elliptically anisotropic eikonal equation to describe the traveltime fields of surface waves on undulated topography. The sensitivity kernel of the traveltime objective function with respect to shear wave velocity is derived using the adjoint‐state method. As a result, the newly developed method is inherently applicable to any study regions, whether with or without significant topographic variations. Hawaii is one of the most seismically and magmatically active regions. However, its significant topographic variations have made it less accurate to investigate using conventional surface wave traveltime tomography methods. To tackle this problem, we applied our new method to invert ambient noise Rayleigh wave phase traveltimes and construct a 3D shear wave velocity model. Our results reveal features that are consistent with geological structures and previous tomography results, including high velocities below Mauna Loa Volcano and Kilauea Volcano, and low velocities beneath the Hilina Fault Zone. Additionally, our model reveals a high‐velocity anomaly to the South of Hualalai's summit, which may be related to a buried rift zone. Our findings further demonstrate that including topography can lead to a correction of up to 0.8% in the shear wave velocity model of Hawaii, an island spanning approximately 100 km with volcanoes reaching elevations exceeding 4 km. Plain Language Summary: Surface wave traveltime tomography is a commonly used technique for constructing subsurface shear wave velocity models based on surface wave traveltime measurements, which has been widely used to investigate the structures of the crust and upper mantle. The accuracy of tomography relies on effective forward modeling, that is, computing traveltime fields in a given velocity model. In this study, we employ an elliptically anisotropic eikonal equation to model the traveltime fields of surface waves on undulated topography, ensuring precise forward modeling in regions with significant topographic variations. The inversion of surface wave traveltimes is formulated as an optimization problem constrained by this elliptically anisotropic eikonal equation, which is solved using the efficient adjoint‐state method. We have applied the new tomography method to the Island of Hawaii. High shear wave velocities are revealed beneath the summits and rift zones of Mauna Loa Volcano and Kilauea Volcano, outlining the subsurface structures associated with magma storage and transportation. Key Points: An elliptically anisotropic eikonal equation is used to model the traveltime fields of surface waves on an undulated topographyAn adjoint‐state surface wave tomography method based on the anisotropic eikonal equation is developed to determine shear wave velocityThe case study in Hawaii suggests limited topography influence on velocity anomaly amplitudes in regions comparable or larger than Hawaii [ABSTRACT FROM AUTHOR]

In this work, we present both 1-D and 3-D shear wave velocity (Vs) models of the oceanic crust and uppermost mantle below the Deep OCean Test ARray area, located ∼ 70 km north of the central section of the Gloria Fault, in the eastern North-Atlantic Ocean. The velocity models are inferred from the dispersion of surface waves recorded on ocean bottom seismometers. Dispersion measurements are obtained from the analysis of ambient seismic noise at short periods (< 14 s) and teleseismic surface waves at long periods (> 14 s) using the two-station method. The 1-D Vs model is inferred from the joint inversion of Rayleigh wave phase velocities and Love wave group and phase velocities. The 3-D tomographic model is obtained by inversion of 2-D Love wave group velocity maps as a function of depth, further constrained by the average of Love wave phase velocities obtained from ambient noise (4–9 s) and the average Rayleigh and Love wave phase velocities calculated from teleseismic data (14–44 s). The 1-D Vs model shows a sediment layer with a low velocity of 1.05 km s−1, similar to previous studies in the region. Below the sediments, we find an oceanic crust with velocities ranging from 3.3 to 4.5 km s−1. The model reaches an unusually high velocity of 4.9 km s−1 in a 20 km thick layer at depths between 16 and 36 km. We interpret this fast velocity layer as indicative of the presence of harzburgite, a residue of enhanced melting that might have been formed by the proximity between the Mid-Atlantic Ridge and the Azores mantle plume. At greater depths the velocity decreases, forming a low-velocity zone that reaches a minimum at ∼ 70 km depth, which we interpret as the maximum depth for the lithosphere–asthenosphere boundary. The 3-D model shows a structure that is mostly horizontally layered, with Vs isocontours at 3.5–4.5 km s−1 highlighting oscillations of the crustal structure with wavelengths of ∼25–30 km. These oscillations may be due to changes in the rate of mantle upwelling and magma supply rate. [ABSTRACT FROM AUTHOR]

Africa's continental crust hosts a variety of geologic terrains and is crucial for understanding the evolution of its longest‐lived cratons. However, few of its seismological models are yet to incorporate the largest continent‐wide noise dispersion data sets. Here, we report on new insights into Africa's crustal architecture obtained using a new data set and model assessment product, ADAMA, which comprises a large ensemble of short‐period surface wave dispersion measurements: 5–40 s. We construct a continent‐wide model of Africa's Crust Evaluated with ADAMA's Rayleigh Phase maps (ACE‐ADAMA‐RP). Dispersion maps, and uncertainties, are obtained with a probabilistic approach. This model update, and a crustal taxonomy derived from unsupervised machine learning, reveals that the architecture of Africa's crust can be classified into two main types: primitive (C1: faster velocities with little gradients) and modified (C2–C4: slower velocities in the shallow crust with more pronounced gradients). The Archean shields are "primitive," showing little variation or secular evolution. The basins, orogens, and continental margins are "modified" and retain imprints of surface deformation. The crustal taxonomy is obtained without a‐priori geological information and differs from previous classification schemes. While most of our reported features are robust, probabilistic modeling suggests caution in the quantitative interpretations where illumination is compromised by low‐quality measurements, sparse coverage or both. Future extension of our approach to other complementary seismological and geophysical data sets—for example, multimode earthquake dispersion, receiver functions, gravity, and mineral physics, will enable continent‐wide lithospheric modeling that extends resolution to the upper mantle. Plain Language Summary: The rocks that constitute Africa's crust record the history of different geological periods. We produce a map, for the entire continent, of how fast shear waves travel within these rocks. We obtain this map from ambient noise surface wave vibrations. The ambient noise surface waves are generated from ocean and atmospheric waves that couple with the solid Earth. There are two types: Rayleigh and Love waves and they travel at different speeds for different wavelengths. This property is called dispersion and it is used to tell how fast the shear wave speeds travel within the subsurface rocks. Constructing the final map from ambient noise surface waves requires the solution of a computational imaging problem. We solve the most challenging computational task with a probabilistic approach—using random sampling—and this enables us to also construct associated error maps. The new maps of Africa's crust show new features that have important implications for subsurface geology of the continent. Key Points: A continent‐wide s‐velocity model of Africa's crust is constructed using probabilistic modeling of the largest catalog of dispersion measurementsA crustal taxonomy, derived with unsupervised machine learning, reveals that Africa's crust is one‐third primitive and two‐thirds modifiedArchean shields are primitive and show no secular evolution; basins, orogens, and margins are modified, retaining imprints of deformation [ABSTRACT FROM AUTHOR]

This study is mainly focused on the behavior change of shear waves. These waves propagate through an inhomogeneous sandwiched water-saturated porous layer in between inhomogeneous elastic layer and inhomogeneous sandy half space under the assumption of non-local theory. Different types of inhomogeneities based on the depth of the layers have been considered in terms of elastic moduli and densities of the medium. Due to the availability of fluid in the second layer, we consider loose bonding at the interfaces in between these three layers, as fluid movement through the interfaces may be possible. A complex dispersion equation has been derived with respect to the boundary conditions. Real and imaginary parts of the dispersion equation provide us with the phase velocity of shear wave and dissipation due to loose bonding at the interfaces, respectively. This dispersion equation has been solved numerically with the help of Newton Raphson method. For validation of the present problem, the numerical solution of dispersion equation has been depicted here graphically in terms of phase velocity c c 2 of shear wave vs. non-dimensional wave number k H 1 (where k is the wave number and H 1 is the thickness of the second porous layer). Also, we discuss about the impact of depth ratios, inhomogeneity of the medium, non-local parameters, loose bonding, and porosity of the sandwiched layer on the propagation of the shear wave. [ABSTRACT FROM AUTHOR]

This study uses ambient noise and earthquake waveform data recorded over ~25 broadband seismic networks in the Himalayas, Tibet, and the Pamir-Hindu Kush to compute a 3-D shear wave velocity (Vs) model of the crust beneath the Kohistan and Ladakh arcs. The velocity model, with a lateral resolution of ~30 km, is derived using a Bayesian hierarchical trans-dimensional inversion of fundamental mode Rayleigh wave group velocity dispersion measurements. The result shows evidence of a uniform upper and middle crust (Vs ~ 3.5-3.6 km/s) underlain by an anomalous high-velocity layer (HVL) with Vs >4 km/s at depths exceeding 40 km beneath the Kohistan arc, consistent with laboratory-derived crustal models showing its pre-collisional structures. The thickness of the HVL is maximum (>20 km) in southern Kohistan, which exposes the mafic and ultramafic arc crust. In contrast, the Ladakh arc, which has seismic structures similar to those in southern Tibet, is characterized by significantly low velocities (Vs < 3.4 km/s) in the middle crust (20-40 km depth) and a relatively thin HVL (~5-10 km) above a Moho depth, which mostly varies between 60 and 72 km. The contrasting velocity structure indicates that the Kohistan arc preserves a typical arc-like crust, whereas the Ladakh arc has undergone significant modifications since the India-Asia collision. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) devices have been used in biochemical assays due to their high sensitivity. The device sensitivity is a function of changes in the density and viscosity of the liquid. Here, we studied the effect of fluid viscosity using a 250 MHz quartz shear-horizontal (SH)-SAW biosensor by monitoring different concentrations of binary aqueous/glycerol solutions. In this study, the sensitivity of the biosensor was determined by fitting the data to models derived from perturbation theory. Measurements in water were used as the reference. For a 0% to 50% glycerol solution, an 87°–204° separation in the phase shift was observed. The slope of the plot of the phase shift vs (ηρ)0.5 was used to indicate the sensor's sensitivity. The sensitivity for our 250 MHz quartz SH-SAW sensors was calculated to be 3.7 × 1 0 − 3 m 2 s Kg . The corresponding mass sensitivity was determined to be 9.25 × 105 m 2 Kg . The limit of detection was calculated to be 36 picograms (pg), while the limit of quantification or LOQ was calculated to be 109 pg. Traditionally, liquid phase measurements have been challenging for SAW devices because liquids dampen the vibrating sensors severely. This problem has been largely solved using a transverse (shear) wave instead of the more popular longitudinal or Rayleigh waves. Liquid measurements are now possible using transverse waves, also known as shear waves, because transverse waves are only minimally attenuated by liquids. Shear-horizontal SAW sensors (SH-SAW) show great promise as label-free biosensors because of their ability to handle liquid samples. However, the viscosity of the liquid still induces loading effects and can be measured when the liquid is loaded onto the SH-SAW propagating surface (delay line). When the liquid above the delay line is perturbed by physical or chemical changes, such as binding to a receptor, it alters the propagating acoustic wave. The SH-SAW device can measure these changes in liquid properties as a change in the wave's phase compared to the original wave. The device's phase shift was recorded as a function of the changes in the density and viscosity of the binary glycerol solution and used to determine the sensitivity in the linear dynamic range of responses. [ABSTRACT FROM AUTHOR]

In this work, an analysis of the propagation of horizontally polarized magnetoelastic shear waves at a loosely bonded interface between two fiber-reinforced (FRC) media is performed. The assumption is that the upper layer is a heterogeneous FRC medium with initial stress, while the lower layer is an FRC half-space subject to gravity. A closed-form expression of the dispersion equation has been derived using Whittaker's function and its asymptotic expansion for both exponential and linear types of heterogeneous cases. The obtained dispersion equation matches well with previously existing results and the classical Love wave equation. In both cases, it was found that the magnetoelastic coupling parameters, horizontal compressive initial stresses, loosely bound, and Biot's gravity parameter of the layered structure all have a favoring effect on the phase velocity. It was also observed that in the linear heterogeneous case, the magnetoelastic coupling parameter has a detrimental influence on the speed of shear wave propagation, while in the exponential heterogeneous situation, it has a beneficial impact. The findings of this study can be used to improve analysis in the fields of geotechnical engineering and civil engineering. This study examines the characteristic behavior of horizontally polarized magnetoelastic shear wave propagation in an inhomogeneous fiber reinforced layer overlaying a fiber-reinforced half-space in the presence of initial stress and gravity. Reinforced materials are now one of the fundamental necessities of building projects of any significant magnitude. In addition, it is crucial to consider the impact of loose bonding at the common interface between the layer and the half-space while building the sensors to improve their efficacy and ultimately achieve high performance. This work is relevant to geotechnical and civil engineering applications and is innovative. Examining the effect of various nondimensional parameters' responses to wave motion is of great interest to researchers due to the immense practical and economic potential of composite structures made from such materials. The present article may have numerous applications in the disciplines of space exploration, aviation, construction, geophysics, geomechanics, and so on. [ABSTRACT FROM AUTHOR]

Recently, supershear Rayleigh waves (SRWs) have been proposed to characterize the biomechanical properties of soft tissues. The SRWs propagate along the surface of the medium, unlike surface Rayleigh waves, SRWs propagate faster than bulk shear waves. However, their behavior and application in biological tissues is still elusive. In brain tissue elastography, shear waves combined with magnetic resonance elastography or ultrasound elastography are generally used to quantify the shear modulus, but high spatial resolution elasticity assessment in 10 μm scale is still improving. Here, we develop an air-coupled ultrasonic transducer for noncontact excitation of SRWs and Rayleigh waves in brain tissue, use optical coherent elastography (OCE) to detect, and reconstruct the SRW propagation process; in combing with a derived theoretical model of SRWs on a free boundary surface, we quantify the shear modulus of brain tissue with high spatial resolution. We first complete validation experiments using a homogeneous isotropic agar phantom, and the experimental results clearly show the SRW is 1.9649 times faster than the bulk shear waves. Furthermore, the propagation velocity of SRWs in both the frontal and parietal lobe regions of the brain is all 1.87 times faster than the bulk shear wave velocity. Finally, we evaluated the anisotropy in different brain regions, and the medulla oblongata region had the highest anisotropy index. Our study shows that the OCE system using the SRW model is a new potential approach for high-resolution assessment of the biomechanical properties of brain tissue. [ABSTRACT FROM AUTHOR]

We presented two high‐resolution, three‐dimensional (3D) global P‐ and joint S‐wave velocity models of the whole mantle with a particular focus on the North Pacific realm using our new global tomographic inversion method. The 3D ray tracing based on data‐adaptive block parameterization was implemented to calculate ∼17 million body‐wave absolute travel times and ray paths of multiple classes (e.g., P, S, PP, SSS, PcP, ScSScS, Pdiff, and PKP) recorded by local networks in China, Alaska, and global stations. Rayleigh wave data at 40–250 s was also incorporated for resolution improvement. Compared to previous models, especially at long spatial wavelengths, our new models better exhibited rich variations in the properties of slabs and cratons subducting/subducted into the mantle. The Kurile‐Kamchatka‐Aleutian arc exhibits a distinct and well‐defined pattern of long linear bands characterized by high velocity (high‐Vp, high‐Vs) anomalies. These anomalies descend continuously from the subduction zone and then extend horizontally at the mantle transition zone (MTZ) beneath the Bering Sea, Japan Sea, or alternatively penetrate into the lower mantle below the Okhotsk Sea. We observed there was no slab‐related gap trapped on top of the MTZ beneath the Alaska Peninsula, which was possibly relevant for the subduction of the extinct Kula and Pacific Plates described in previous studies. A further unexpected discovery, deduced from the slab's location and tectonic history, was the identification of a high‐Vp anomaly running parallel to the plate boundary in the Aleutian forearc region, which was considered as an integral part of the Kula slab. Plain Language Summary: The Circum‐North Pacific contains an active North‐Northwestward subduction zone of the ancient Izanagi and Kula Plates and the present Pacific Plate during the Late Mesozoic to Cenozoic. This successive subduction system leads to complex plate tectonics characterized by substantial topographic variations, widespread subduction zones, abundant intraplate volcanic activities, and ancient craton lithospheric deformation. Here we image high‐resolution P‐ and S‐wave velocity models, which were inverted by our updated global tomographic method using data containing more than 17 million body and surface wave measurements. Our models indicate no gaps at the top of the mantle transition zone, and it differs from the previous studies beneath the Aleutian Arc. In addition, two parallel high‐Vp belts are imaged on both sides of the Aleutian Arc between ∼300 and 1,000 km depth, which were considered as part of the remnant Kula slab and present Pacific slab. These findings provide both a good understanding of the slab geometry and evolution associated with multiple plate subduction in the North Pacific subduction zone and an example to understand the way how the Earth's interior works. Key Points: Global P‐ and S‐wave tomography models were determined for the North Pacific by the joint inversion of body wave and Rayleigh wave dataMassive‐slab‐related high‐velocity anomalies revealed the geometries of the subduction slabs under the North Pacific realmTwo subparallel high‐velocity belts have presumably related to the subduction of the Pacific and Kula slabs [ABSTRACT FROM AUTHOR]

We present a novel strategy for joint modelling to estimate shear wave velocities at ten sites in Dhanbad City, India. The joint modelling technique utilizes the complementary sensitivities of disparate datasets, such as horizontal-to-vertical spectral ratios (HVSR) and Rayleigh wave phase velocity dispersion curves, obtained from passive and active seismic surveys, respectively. The model search space is explored rigorously via the very fast simulated annealing (VFSA) global optimization technique and uncertainties are quantified with estimates of marginal posterior probability distributions (PPDs) and parameter correlation matrices (PCMs). These tools help us identify the portions of acceptable models that are well, or poorly, constrained. A confirmatory test is conducted to demonstrate the effectiveness of the modelling scheme by synthetic data as well as field data recorded in Dhanbad City. The depth to engineering bedrock is found to reach its maximum (~ 42 m) and minimum (~ 9.5 m) in the southwestern and northeastern parts of the city, respectively, while dominant frequencies range between 2 and 14.6 Hz. The largest Vs30 value found is 562 m/s at Dhanbad's southern border and 351 m/s in south-central neighbourhoods. Shear wave velocity profiles are consistent with borehole lithology data. The seismic characterization of Dhanbad City presented here will aid in seismic hazard mitigation efforts and facilitate infrastructure that can sustain the dynamic load imposed by earthquakes. [ABSTRACT FROM AUTHOR]

Deep sedimentary valleys entrap and amplify seismic waves, which is further responsible for site-specific amplification over the allied region. Kashmir valley is a deep and active sedimentary basin in the northwest portion of the Himalayan lap. To characterize the site response for the intermountain Kashmir valley for the first time, we acquire single station microtremor measurements using Lennartz (three components/5s seismometer) at 141 sites with a grid of (5 km × 5 km) and two-dimensional (2D) array measurements using seven units of recording station of different geometry pattern at 38 sites across different lithological setup within the basin. We present here (1) a first-order predominant fundamental frequency (0.21–10.19 Hz) and subsequent sedimentary thickness maps for the entire valley, reflecting deep deposition with spatial heterogeneity in the area using the horizontal-to-vertical spectral ratio (HVSR) technique; (2) spatial classification of generated HVSR curves linking subsurface geomorphology and post strong ground-motion scenario in the valley; (3) extraction of the best dispersion characteristics of Rayleigh waves (fundamental mode) from all recorded vertical signals at each array site using frequency–wavenumber (F-K) method with an emphasis on signal synchronicity; and (4) retrieval of one-dimensional (1D) shear wave velocity (VS) profiles across the valley from the inversion of dispersion curves using the neighborhood algorithm. Distinct model parameterizations were tested for the inversion to achieve the optimal inversion misfit. The collocated 1D VS profiles are consistent with newly drilled borehole logs information. Besides, the presented first-ever ambient noise survey–based site response study meets the objectives of site-specific seismic hazard and risk analysis of the Kashmir valley at the regional scale. [ABSTRACT FROM AUTHOR]

A new 3D S-velocity model for the crust and upper mantle beneath the Yellow Sea, the East China Sea, the Japan Sea, and the Philippine Sea is determined by means of Rayleigh-wave analysis for depths ranging from 0 to 400 km, and the most conspicuous features of the earth structure in this region are revealed from this model. In the depth range from 5 to 30 km, the S-velocity is principally affected by the thickness of the crust. In the areas with thin crust (oceanic crust), the highest S-velocity values are determined, while the lower S-velocity values are shown for the areas with a transitional crust. For the Japan Sea, the decrease observed in crustal thickness towards the north can be the result of the back-arc spreading that formed this sea from 32 to 10 Ma. Thus, from the four models proposed to explain the oceanic structure of this sea, the model supported by the results determined in the present study is the back-arc spreading model. For the Philippine Sea, the difference in the type of crust determined for the western part and the eastern-northeastern part is consistent with the two different theories, proposed to explain the origins of both parts of this sea. In the depth range from 30 to 60 km, the western part of the Philippine Sea shows higher S-velocity values than the eastern part, because the age of western part of this sea is greater than that of eastern part. The S-velocity difference of 0.2 km/s determined between both parts of this sea implies that the temperature difference within the lithosphere may reach ~370°C. For the western part of this sea, the controversy between the previous different lithospheric-thickness determinations is solved in the present study determining a lithosphere thickness of 90 km. The Japan Sea, the East China Sea, and Okinawa Trough are characterized by thin lithosphere, thick asthenosphere, and low S-velocities. These results and other evidence suggest that from the two models proposed to explain the formation of East Asian rifting system, the model of the back-arc spreading is the most realistic model. The asthenosphere beneath all study area has been precisely located and mapped in S-velocity, for the first time. The Pacific and Philippine Sea slabs and their corresponding mantle wedges above the slabs are also mapped with S-velocities. [ABSTRACT FROM AUTHOR]

The inversion of the Rayleigh wave dispersion curve is a crucial step in obtaining the shear wave velocity (VS) of near-surface structures. Due to the characteristics of being ill-posed and nonlinear, the existing inversion methods presented low efficiency and ambiguity. To address these challenges, we describe a six-layer deep neural network algorithm for the inversion of 1D VS from dispersion curves of the fundamental mode Rayleigh surface waves. Our method encompasses several key advancements: (1) we use a finer layer to construct the 1-D VS model of the subsurface, which can describe a more complex near-surface geology structure; (2) considering the ergodicity and orderliness of strata evolution, the constrained Markov Chain was employed to reconstruct the complex velocity model; (3) we build a practical and complete dispersion curve inversion process. Our model tested the performance using a random synthetic dataset and the influence of different factors, including the number of training samples, learning rate, and the selection of optimal artificial neural network architecture. Finally, the field test dispersion data were used to further verify the method's effectiveness. Our synthetic dataset proved the diversity and rationality of the random VS model. The results of training and predicting showed higher accuracy and could speed the inversion process (only ~15 s), and we proved the important effect of different factors. The outcomes derived from the application of this technique to the measured dispersion data in the Yellow River Delta exhibit a strong correlation with the outcomes obtained from the integration of the very fast simulated annealing method and the downhill simplex method, as well as the statistically derived shear wave velocity data of the sedimentary layers in the Yellow River Delta. From a long-term perspective, our method can provide an alternative for deriving VS models for complex near-surface structures. [ABSTRACT FROM AUTHOR]

A numerical investigation of surface wave propagation in the surface wave exploration of river embankments is implemented using 3D shallow soil models with different subsurface shapes and S-wave velocities. The focus is on the effects of surface and subsurface irregularities on the propagation and dispersion characteristics of Rayleigh waves generated by a surface source and observed at points along the crest of the embankment. Rayleigh wave dispersion curves observed along the embankment crest are found to be contaminated by reflected waves, with the amount of contamination affected more by the position of the velocity boundary at the bottom edge of the embankment than the surface topography. When the velocity boundary is close to the ground surface, especially at the toe of the slope, the effect of reflected waves is sufficiently large to generate biases in the phase velocity estimates. [ABSTRACT FROM AUTHOR]

The Lonar impact crater in the Deccan Volcanic Province of India is an excellent analogue for impact-induced structures on the Moon and other terrestrial planets. We present a detailed architecture of the crater using a high-resolution 3-D seismic velocity image to a depth of 1.5 km through the inversion of high-frequency ambient noise data recorded over 20 broad-band seismographs operating around the crater. The ambient noise waveform is dominated by cultural noise in the 1–10 Hz band. The shear wave velocity (Vs) model is created from Rayleigh wave group velocity data with a horizontal resolution of 0.5–1 km in the period range of 0.1–1.2 s. A key feature of the model is a velocity reduction of 10–15 per cent below the crater compared to outside the ejecta zone. The low-velocity zone below the crater is nearly circular and extends to a depth of ∼500 m. This estimated crater's depth is consistent with global depth–diameter scaling relations for simple craters. The basement, with a Vs of more than 2.5 km s−1, lies beneath the Deccan basalt, which has a Vs of ∼2.4 km s−1. These results are consistent with laboratory-measured data from the Lonar crater and borehole data in the western Deccan trap. This study opens a new window for exploring impact craters and sub-basalt structures using high-frequency ambient noise tomography. [ABSTRACT FROM AUTHOR]

High-resolution seismic image is critically important for mining minerals. In this study, we collected seismic data from a local dense seismic array consisting of 154 stations around the Anyuan mining area and its adjacent region of Pingxiang City, Jiangxi Province in South China, and applied the ambient noise tomography (ANT) method to image the shear wave velocity structure in the study area. Shallow crustal velocities at depths less than 3.3 km were determined by direct inversion of Rayleigh wave group velocity dispersion curves at the period range of 0.5–5.0 s. Overall, the S-wave velocity structure has a tight correlation with surface geological and tectonic features in the study area. The shear wave velocity structure in the shallow crust of the Anyuan Mine and its adjacent areas displayed distinct low-velocity anomalies, which can be attributed to the depression of sedimentary structures and coal mining activities in the Pingxiang-Leping region. The zones surrounding the Anyuan fault (AYF) and Wangkeng fault (WKF) zones exhibited low-velocity anomalies from the ground surface to ~ 3.3 km underground. And the low-velocity anomalies at depths less than 1.2 km could be related to the sedimentary environment of coal mine and the coal mining activities, while the low-velocity anomalies at depths below 1.2 km are caused by the presence of fracture medium, oil and gas in the fault zone. The shear wave velocity changes sharply across the AYF, and the characteristics of the velocity change interface indicate that the AYF is inclined toward the northwest, with its extension reaching depths of approximately 3 km underground. [ABSTRACT FROM AUTHOR]

To test the relationship between plate age and uppermost mantle structure for the Juan de Fuca and Gorda plates, as well as the mode of lithospheric cooling, we produce a new 3D oceanic shear wave speed (VS) model. This model is constructed using a new high‐quality Rayleigh wave phase speed data set across the plates and is based on a novel thermo‐seismic hybrid parameterization. In the lithosphere, we find that the VS structure is primarily (68% of study area) governed by conductive cooling. Exceptions are observed, suggesting advective heat influx along ridges and hydrothermal circulation through cracks near the subduction trench and transform faults. In the asthenosphere of the Juan de Fuca plate, no simple monotonic relationship between seismic structure and plate age exists, but instead there is a non‐monotonic slow‐fast‐slow VS pattern from west to east. The two slow asthenospheric VS anomalies indicate the presence of partial melt beneath both the mid‐ocean ridge and the subduction trench. The partial melt beneath the trench is enigmatic. Plain Language Summary: Previous studies have demonstrated that the uppermost mantle structure across oceanic plates varies significantly with plate age. To explore the relation between the uppermost mantle structure and the plate age of small and young oceanic plates in higher resolution, we generate a new 3D shear wave speed (VS) model across the entire Juan de Fuca and Gorda plates using seismic surface wave data. Our model shows that conductive cooling is the primary cause controlling the lithospheric structure in most of the Juan de Fuca and Gorda plates. Near plate boundaries, other causes such as advective heat transport, plate deformation, and mantle hydration may have an additional influence. This suggests that conductive cooling is a valid assumption for young plate ages and is significant on spatial scales as small as the resolution of our model (80 km). In the underlying asthenosphere, our VS model shows a slow VS near the mid‐ocean ridge, fast enough to be considered melt‐free near the age of 4.5 Ma, and slow again near the trench. The mechanism behind this slow‐fast‐slow pattern is still enigmatic. Key Points: A shear wave speed model for the Juan de Fuca and Gorda plates is constructed using a novel thermo‐seismic hybrid parameterizationTwo thirds of lithospheric structure agrees with plate age, with deviations attributable to heat advection or plate deformationMelt may be present beneath the Cascadia trench near a depth of 100 km, but its source is unclear [ABSTRACT FROM AUTHOR]

Brittle materials fail by means of rapid cracks. Classical fracture mechanics describes the motion of tensile cracks that dissipate released elastic energy within a point-like zone at their tips. Within this framework, a “classical” tensile crack cannot exceed the Rayleigh wave speed, cR. Using brittle neo-hookean materials, we experimentally demonstrate the existence of “supershear” tensile cracks that exceed shear wave speeds, cR. Supershear cracks smoothly accelerate beyond cR, to speeds that could approach dilatation wave speeds. Supershear dynamics are governed by different principles than those guiding “classical” cracks; this fracture mode is excited at critical (material dependent) applied strains. This nonclassical mode of tensile fracture represents a fundamental shift in our understanding of the fracture process. [ABSTRACT FROM AUTHOR]

Featured with a higher velocity, increased power handling capability, and better aging behavior, surface transverse wave (STW) shows more promising prospects than Rayleigh wave nowadays in various sensing applications. The need to design, optimize, and fabricate the related devices motivates the development of modeling and simulation. For this reason, a three-dimensional (3D) finite element (FE) simulation of STW on quartz, considering the crystal cut angle and the electrode effects, is presented in this study. Firstly, we investigated the effects of quartz's cut angle on the generated waves. Here, the polarized displacements were analyzed to distinguish the wave modes. Secondly, the investigations of the electrode effects on the polarized displacement, phase velocity, and electromechanical coupling factor (K²) were carried out, for which different material and thickness configurations for the electrodes were considered. Thirdly, to examine the excitation conditions of the generated waves, the admittance responses were inspected. The results showed that not only the crystal cut angle but also the density and the acoustic impedance of the interdigital transducer (IDT) material have a strong influence on the excited waves. This article is the first to analyze STWs considering quartz's cut angle and electrode effect through a 3D FE model. It could provide a helpful and easy way to design, optimize, and fabricate the related surface acoustic wave devices. [ABSTRACT FROM AUTHOR]

The non-invasive evaluation of the heart through EectroCardioGraphy (ECG) has played a key role in detecting heart disease. The analysis of ECG signals requires years of learning and experience to interpret and extract useful information from them. Thus, a computerized system is needed to classify ECG signals with more accurate results effectively. Abnormal heart rhythms are called arrhythmias and cause sudden cardiac deaths. In this work, a Computerized Abnormal Heart Rhythms Detection (CAHRD) system is developed using ECG signals. It consists of four stages; preprocessing, feature extraction, feature optimization and classifier. At first, Pan and Tompkins algorithm is employed to detect the envelope of Q, R and S waves in the preprocessing stage. It uses a recursive filter to eliminate muscle noise, T-wave interference and baseline wander. As the analysis of ECG signal in the spatial domain does not provide a complete description of the signal, the feature extraction involves using frequency contents obtained from multiple wavelet filters; bi-orthogonal, Symlet and Daubechies at different resolution levels in the feature extraction stage. Then, BlackWidowOptimization (BWO) is applied to optimize the hybrid wavelet features in the feature optimization stage. Finally, a kernel based Support Vector Machine (SVM) is employed to classify heartbeats into five classes. In SVM, Radial Basis Function (RBF), polynomial and linear kernels are used. A total of ~15000 ECG signals are obtained from the Massachusetts Institute of Technology-Beth Israel Hospital (MIT-BIH) arrhythmia database for performance evaluation of the proposed CAHRD system. Results show that the proposed CAHRD system proved to be a powerful tool for ECG analysis. It correctly classifies five classes of heartbeats with 99.91% accuracy using an RBF kernel with 2nd level wavelet coefficients. The CAHRD system achieves an improvement of ~6% over random projections with the ensemble SVM approach and ~2% over morphological and ECG segment based features with the RBF classifier. [ABSTRACT FROM AUTHOR]

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Copyright of Petroleum Geology & Recovery Efficiency is the property of Petroleum Geology & Recovery Efficiency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To investigate the dominant deformational patterns and stress conditions in the upper crustal structure of the Kinki region, southern-central Japan, we constructed a high-resolution 3D azimuthal anisotropy model to a depth of ~ 11 km. We used 6-month-long ambient noise data recorded by the densely distributed permanent and temporary stations. From this dataset, cross-correlations were retrieved. We then obtained a 3D isotropic velocity model by inverting Rayleigh wave dispersion data, followed by a direct joint inversion for both 3D azimuthal anisotropy and additional isotropic velocity perturbation. The resolved 3D azimuthal anisotropy reveals significant contrasts of anisotropy across the Kinki region. The predominant fast axes observed in the northwestern Kinki region align with the direction of the maximum horizontal compressional stress and the principal strain rate axes, suggesting that the observed anisotropy is mainly stress-induced. In the southern part of the study area, furthermore, the predominant fast axes trend NE–SW and near E–W, also indicating the presence of stress-induced anisotropy. On the depth profile of the anisotropy, we found depth-dependent variation of azimuthal anisotropy. There exists a significant consistency between the anisotropy observed beneath 3 km depth and the dense distribution of earthquake hypocenters. This interrelationship between anisotropy and seismicity demonstrates that the observed anisotropy could be linked to local crustal stress or fractures relevant to earthquake ruptures. Our 3D anisotropy model therefore contributes towards understanding the locations and features of the seismicity region. [ABSTRACT FROM AUTHOR]

Background: In limited resource settings, identification of factors that predict the occurrence of pulmonary hypertension(PH) in children with atrial septal defect(ASD) is important to decide which patients should be prioritized for defect closure to prevent complication. Echocardiography and cardiac catheterization are not widely available in such settings. No scoring system has been proposed to predict PH among children with ASD. We aimed to develop a PH prediction score using electrocardiography parameters for children with ASD in Indonesia. Methods: A cross-sectional study reviewing medical record including ECG record was conducted among all children with newly diagnosed isolated ASD admitted to Dr Sardjito Hospital in Yogyakarta, Indonesia during 2016–2018. Diagnosis of ASD and PH was confirmed through echocardiography and/or cardiac catheterization. Spiegelhalter Knill-Jones approach was used to develop PH prediction score. Accuracy of prediction score was performed using a receiver operating characteristic (ROC) curve. Results: Of 144 children, 50(34.7%) had PH. Predictors of pulmonary hypertension were QRS axis ≥120°, P wave ≥ 3 mm at lead II, R without S at V1, Q wave at V1, right bundle branch block (RBBB), R wave at V1, V2 or aVR > normal limit and S wave at V6 or lead I > normal limit. ROC curve from prediction scores yielded an area under the curve (AUC) 0.908(95% CI 0.85–0.96). Using the cut-off value 3.5, this PH prediction score had sensitivity of 76%(61.8–86.9), specificity 96.8%(91.0-99.3), positive predictive value 92.7%(80.5–97.5), negative predictive value 88.4%(82.2–92.6), and positive likelihood ratio 23.8(7.7–73.3). Conclusions: A presence of PH in children with ASD can be predicted by the simple electrocardiographic score including QRS axis ≥120°, P wave ≥3 mm at lead II, R without S at V1, Q wave at V1, RBBB, R wave at V1, V2 or aVR > normal limit and S wave at V6 or lead I > normal limit. A total score ≥ 3.5 shows a moderate sensitivity and high specificity to predict PH among children with ASD. [ABSTRACT FROM AUTHOR]

The use of surface wave measurements to derive an S -wave velocity profile of the subsurface has become a widely applied procedure; however, their potential use to reconstruct the S -wave material damping properties of the subsoil is generally overlooked, due to the difficulties in obtaining consistent surface wave amplitude information from field data and translating them into robust estimates of the dissipative properties of the near-surface. In this work, we adapt a wavefield decomposition technique for the processing of elastic surface wave data to the extraction of the complete set of properties of Rayleigh waves generated by a controlled source and propagating in dissipative geomaterials. Retrieved information includes multimodal phase velocity and ellipticity as well as the frequency-dependent attenuation coefficient. We exploit the key advantages of wavefield decomposition processing (joint interpretation of multicomponent recordings, coupled estimation of wave propagation parameters, modelling of multiple superimposing modes) to maximize the robustness of the retrieval of Rayleigh wave properties, especially of the dissipative ones. For the subsequent interpretation of Rayleigh wave dispersion, ellipticity and attenuation data we implement a joint Monte Carlo inversion yielding a coupled estimate of S -wave velocity and damping ratio profile for the subsurface; we incorporate a series of geophysical constraints to narrow down the searched parameter space to realistic soil models. We apply this processing and inversion scheme to a bespoke synthetic data set and to a field survey for the characterization of a strong motion station; in both cases, we succeed in retrieving Rayleigh wave multimodal dispersion, ellipticity and attenuation curves. From the inversion of data from the simulated seismogram we are able to reconstruct the properties of the synthetic model. As for the real case, we determine an S -wave velocity and damping ratio model for the soil column below the station, through which we are able to model the inelastic earthquake local response observed at the site. Basing on the results obtained for the real case, we argue that one of the advantages brought by our processing method—the possibility to process active Rayleigh wave data acquired by a 2-D array illuminated by different source positions—may play a key role in allowing to retrieve dissipative properties of the near-surface closer to the material damping of the soil materials, and less influenced by scattering determined by possible discontinuities in the subsurface. [ABSTRACT FROM AUTHOR]

Evaluating the variability components of ground motion models and their reduction is important for site-specific hazard assessment. We compared the observed and median-predicted ground motions resulting from recent ground motion prediction equations (GMPEs) in the Western Himalayan region to evaluate the performance of ground motion models (GMMs) in a non-ergodic framework. We study two methods to compute the residuals obtained from the observed and predicted ground motions; they are a pooled ordinary least-squares model and a mixed-effects regression model. Comparison of results from both the models shows that the former is more accurate than the latter for describing ground motion residuals and their variability. We analyzed total residuals and their components such as the between-event and within-event residuals for peak ground acceleration (PGA) to investigate the impact of source, path, and site effects on the GMM variability. The total residuals for the GMPE by Ramakrishnan et al. (J Earthquake Eng. https://doi.org/10.1080/13632469.2019.1605318, 2019) are scattered around zero for a wider magnitude and distance range. Their distance-dependence varies with magnitude; they exhibit a scatter around zero for Mw = 6–6.9 in the analyzed distance range 0–1200 km. Between-event residuals do not show clear magnitude dependence; their scatter at larger distances is reduced due to scattering from medium heterogeneities. The within-event residuals show a trend with distance. The standard deviation associated with distribution of within-event residuals is slightly more than that for the between-event residuals, meaning the dominance of within-event variability in the model parameters. The features such as complexity in site effect, alongside regional differences in shear wave speed structure and near-surface attenuation, are not completely captured by the reference GMPE, which needs further investigation with redundant measurements of source, propagation (path), or site effects for site-specific hazard assessments of the region in a fully non-ergodic framework. [ABSTRACT FROM AUTHOR]

The Eastern Indian Ocean is a tectonically and geodynamically active region that has experienced deformations due to rifting, uplifting, and plume activity. The earlier Rayleigh wave studies in the East Indian Ocean were mainly focused on the structure of the Bay of Bengal, Ninety East Ridge, and Broken Ridge. The structure of other region of the East Indian Ocean is not much explored. In the present study, Rayleigh wave dispersion analysis is performed to observe the signatures of upper mantle deformation in terms of shear wave velocity of the East Indian Ocean using global search method. The fundamental mode Rayleigh wave group velocities are estimated between 15 and 100 s using the multiple filter technique. The group velocities of the raypaths that traverse the same region are clustered (E1–E8) to get an average dispersion curve. Using a genetic algorithm, each cluster's group velocities are inverted for shear velocity structure. The observed dispersion curve of E6, E7, and E8 indicates the lower group velocities between 35 and 100 s relative to E1, E2, E3, E4, and E5, with an average variation of about 0.07–0.18 km/s. The crustal thickness obtained in the study region is ~ 26 km and is due to the increased thickness of the lower crust (9.1–12.4 km) having Vs 3.95–4.04 km/s. The theoretical Vs have been calculated for serpentinite rock at uppermost lithospheric conditions and found to be similar to the Vs of the lower crust in the present study. Hence, it is assumed that unusual crustal thickness is due to the progressive development of the upper lithosphere formation (Ultramafic rock) into material (serpentinite rock) with crustal-like shear velocity or moderately lower than sub-Moho shears velocity. The undeformed lithosphere is evidenced by the high-velocity (Vs 4.62–4.77 km/s) layer beneath the Moho, whose thickness ranges from 41.3 to 51.6 km. The high-velocity lithosphere is followed by a low-velocity zone that extends up to 160 km; however, the variation in Vs (4.57–4.31 km/s) indicates that the low-velocity zone is deformed. [ABSTRACT FROM AUTHOR]

In this work, the Moho depth and the velocity structure of the crust and upper mantle beneath broad-band seismic stations of the Algerian broad-band seismic network are investigated. Teleseismic P -wave receiver functions jointly inverted with Rayleigh wave dispersion curves obtained from local earthquakes have been used. The seismic stations are located in different geological settings including the Tell Atlas, High Plateaus and the Saharan Atlas. The crustal thickness and the V p/ V s ratio are first derived by the H–κ stacking method of receiver functions. The inversion results show the variation in Moho depth in the different geological contexts. The shallowest depths of the Moho (∼20–30 km) are estimated along the Algerian continental margin and Tell Atlas. In the High Plateaus region, the Moho depths vary from 30–36 km, whereas the deepest Moho depths are found in the Saharan Atlas (36–44 km). Two-layer crust is observed in the whole study area. In the upper crust, ∼8–14 km thick, the average shear wave velocity is ∼3.0 km s−1. The lower crust of about 12–30 km thick has an average shear wave velocity that ranges between 3.4 and 3.8 km s−1. The lower crust is thicker than the upper crust particularly in the Saharan Atlas. The upper mantle shear wave velocity varies from 4.1 to 4.5 km s−1 maximum and is stable, generally, below ∼60 km depth. Two low-velocity zones are clearly observed particularly in the eastern part of the Tell Atlas and the High Plateaus. The first one about 10 km thick is in the lower part of the lower crust and the other one is in the upper mantle between 40 and 60 km depth. The obtained results are in accordance with the previous results found in the region, particularly those using land gravity and seismic data. As the first estimate of the Moho depth from earthquake data in northern Algeria, using the receiver function method, this study sheds new light on the crustal structure and the Moho depth in this region of the world. [ABSTRACT FROM AUTHOR]

Earthquakes are destructive natural hazards with damage capacity dictated by rupture speeds. Traditional dynamic rupture models predict that earthquake ruptures gradually accelerate to the Rayleigh wave speed with some of them further jumping to stable supershear speeds above the Eshelby speed (~ 2 times S wave speed). However, the 2018 Mw 7.5 Palu earthquake, among several others, significantly challenges such a viewpoint. Here we generate spontaneous shear ruptures on laboratory faults to confirm that ruptures can indeed attain steady subRayleigh or supershear propagation speeds immediately following nucleation. A self-similar analysis of dynamic rupture confirms our observation, leading to a simple model where the rupture speed is uniquely dependent on a driving load. Our results reproduce and explain a number of enigmatic field observations on earthquake speeds, including the existence of stable subEshelby supershear ruptures, early onset of supershear ruptures, and the correlation between the rupture speed and the driving load. Earthquake rupture speeds significantly impact seismic hazards. Here, authors report laboratory earthquake experiments reproducing early and stable subEshelby supershear ruptures, and unlocking the correlation between rupture speed and driving load. [ABSTRACT FROM AUTHOR]

The Rayleigh mode (also called generalized Rayleigh wave) at the flat interface between a liquid and a double porosity medium saturated by the same liquid, is investigated. The double porosity medium obeys the phenomenological model of Berryman and Wang (2000). It allows the simultaneous propagation of three longitudinal waves and a transverse wave. Assuming open pore conditions at the interface, formulas are found for the coefficients of reflection in the liquid and of transmission in the double porosity medium. Considering only the angular variable in the study, numerical simulations based on data for Berea sandstone show the influence of frequency and the two types of porosity on the reflection coefficient and on the velocity of the generalized Rayleigh wave. [ABSTRACT FROM AUTHOR]

Shear waves are employed in medical ultrasound imaging because they reveal variations in viscoelastic properties of soft tissue. Frequencies below 1 kHz are required due to the substantially higher attenuation and lower propagation speeds than for compressional waves. Shear waves exhibiting particle motion in the direction of propagation, referred to as longitudinal shear waves, can be generated with longitudinal motion of a circular disk on the surface of a soft elastic medium. This approach permits imaging of the longitudinal shear wave with a conventional ultrasound transducer that is coaxial with the source of the shear wave. Presented here is a mathematical model describing the complete wave field generated by displacement at the surface of an isotropic elastic half-space. Numerical simulations are shown for longitudinal, transverse, torsional, and radial source polarizations, with emphasis on focused longitudinal shear waves. Predictions are consistent with measurements of light beams revealing that the longitudinal electric field component produces a smaller focal spot than the transverse field component [Dorn, Quabis, and Leuchs, Phys. Rev. Lett. 91, 233901 (2003)]. Simulations are compared with preliminary measurements of a focused longitudinal shear wave beam generated in a soft tissue phantom by longitudinal motion of a spherically concave piston. [ABSTRACT FROM AUTHOR]

The formation of a new ocean basin provides a unique observational window into the structure and deformation of the oceanic lithosphere. This study offers a detailed 1‐D vertically polarized shear‐wave velocity model of the young Japan Basin by interpreting S receiver functions, seafloor Rayleigh wave ellipticities and phase velocities in a Bayesian trans‐dimensional framework. The models suggest a distinct discontinuity in the mid‐lithosphere. Additional analyses indicate that the upper layer is characterized by strong positive radial anisotropy, while the lower layer is more isotropic. We interpret that the upper layer was formed during the back‐arc opening at 20–15 Ma, where the olivine lattice‐preferred orientation (LPO) fabric induced by passive upwelling contributes to the positive radial anisotropy. The lower, less anisotropic layer may be solidified after the sudden cessation of the opening. Small‐scale convection (SSC) from such a major tectonic event could randomize the LPO enough to weaken radial anisotropy before cooling down the asthenosphere, leaving a radially anisotropic discontinuity in the present‐day mid‐lithosphere. The proposed layered evolution history of the lithosphere beneath the Japan Basin illuminates an important role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Such an SSC‐induced radial anisotropy drop could also occur at the base of the lithosphere in regions with ongoing seafloor spreading and enhance the velocity drop of horizontally polarized shear waves. Thus, the role of SSC is non‐negligible in explaining the sharpness of the Gutenberg discontinuity detected by SS precursors beneath the oceanic lithosphere. Plain Language Summary: The formation of the oceanic lithosphere is associated with a relatively simple mantle convection process called seafloor spreading, but may also be affected by more complex, localized processes such as small‐scale mantle convection. To decipher the evolution history of the lithosphere of the Japan Basin, the Sea of Japan, this study collects earthquake waveforms from broadband ocean‐bottom seismometers and offers a detailed 1‐D seismic structural model beneath the Japan Basin by interpreting the multiple seismological observables in a trans‐dimensional Bayesian framework. Our seismic velocity model and associated analysis reveal that the oceanic lithosphere of the Japan Basin is seismically more complex than expected. The upper and lower parts of the lithosphere show distinct seismic anisotropy properties. We propose a layered evolution model for the lithosphere of the Japan Basin, in which small‐scale convection followed a normal seafloor spreading, and resulted in a structural discontinuity in the present‐day mid‐lithosphere. The proposed model highlights the role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Key Points: We construct detailed 1‐D Vsv models of the Japan Basin by trans‐dimensional inversion of multiple observables extracted from ocean‐bottom seismometers recordsOur analysis reveals a mid‐lithosphere discontinuity arising from strong positive radial anisotropy in the upper lithosphereA layered evolution mode associated with small‐scale convection is proposed for the lithosphere of the Japan Basin [ABSTRACT FROM AUTHOR]

The behavior of surface horizontally polarized shear waves (SH waves) in the composite multi-material structure with a periodic irregular surface and interface is investigated analytically in the present study. To unravel the enshrouded features of the SH-wave propagation in a multi-layer structure, we consider a model of three distinct composite materials. In the schematic of the problem, the guiding layer (M-I) contains fluid-saturated porous materials of finite thickness, the intermediate layer (M-II) contains fiber-reinforced composites, and the substrate contains the functionally graded orthotropic materials (M-III). The free surface of M-I and the upper interface of the medium are considered to be irregular on a periodic basis, but the interface of M-II and M-III is supposed to be regular. The dispersion relation is obtained analytically and demonstrated graphically for the phase velocity versus the wave number to analyze the propagation behavior of the SH-wave propagation in the proposed structure. The acquired results resemble the typical Love wave results, confirming the validity of the present work. The current work provides a comprehensive evaluation of the impact of regular and irregular boundaries of the composite materials on the phase velocity of the SH waves. It is notable that the behavior of the reinforced parameters, initial stress, and porosity on the phase velocity is consistent in both scenarios. More than the irregularity of the free surface, the periodic irregularity of the interface had an impact on the phase velocity. The obtained results are useful to understand the compositions of the materials on the mountain surface. [ABSTRACT FROM AUTHOR]