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Characterization of a productive oil/gas well blowout through seismological methods is relatively uncommon. In this paper, we conduct an in-depth seismic evaluation of one of the world’s most significant onshore oil well blowout incidents, which occurred in 2020 at the Baghjan oil field in Assam, northeast India. We show that the blowout and related on-site activities generated distinct signals that can be distinguished by their spectral characteristics, temporal variation in geometric spreading, and sharp attenuation of daytime noise in comparison to the nighttime. A micro-earthquake potentially triggered by the blowout was also detected. Furthermore, we show how seismic data can be used to reasonably estimate blowout gas exit velocity and flame height. Our results demonstrate that a detailed characterization and spatiotemporal variation of blowout activity can be successfully captured through seismic monitoring, opening new opportunities for hazard mitigation and cost-effective disaster management for such catastrophic events. [ABSTRACT FROM AUTHOR]

Propagation of Rayleigh-type waves is investigated in a half-space composed of nonlocal micropolar thermoelastic material containing void pores. Dispersion relation is derived for a mechanically stress-free and thermally insulated boundary surface of the half-space. The particle motion during the propagation of the waves is found to follow elliptical path. Numerical computations for a specific material are performed to analyze the characteristics of propagating Rayleigh-type waves in detail. Comparison between the phase speed and corresponding attenuation coefficient in some particular cases is also carried out. The effect of various parameters on the characteristics of waves in question is also studied. [ABSTRACT FROM AUTHOR]

Rayleigh waves are crucial in earthquake engineering due to their significant contribution to structural damage. This study aims to accurately synthesize Rayleigh wave fields in both uniform elastic half-spaces and horizontally layered elastic half-spaces. To achieve this, we developed a self-programmed FORTRAN program utilizing the thin layer stiffness matrix method. The accuracy of the synthesized wave fields was validated through numerical examples, demonstrating the program's reliability for both homogeneous and layered half-space scenarios. A comprehensive analysis of Rayleigh wave propagation characteristics was conducted, including elliptical particle motion, depth-dependent decay, and energy concentration near the surface. The computational efficiency of the self-programmed FORTRAN program was also verified. This research contributes to a deeper understanding of Rayleigh wave behavior and lays the foundation for further studies on soil-structure interaction under Rayleigh wave excitation, ultimately improving the safety and resilience of structures in seismic-prone regions. [ABSTRACT FROM AUTHOR]

Laboratory experiments suggest that the evolution of in-plane shear rupture along an interface separating two elastic blocks typically shows a transition from slow to fast slip. In contrast to the commonly used continuum mechanics-based approaches, here we study the shear rupture process along a weak interface using the discontinuous deformation analysis (DDA) method. We incorporate a slip-weakening constitutive friction law to simulate the initiation and propagation of shear rupture under external conditions of a constant normal load and a steadily increased shear load. As the shear load increases, our modeling results reveal a sharp transition from episodic expansion and arrest to unstable runaway rupture, consistent with previous experimental results. In the stage of dynamic runaway, rupture velocity is limited by the Rayleigh wave velocity. We further investigate the effects of external loading conditions including load point velocity and normal stress on rupture behavior. We find that the dynamic rupture velocity increases with load point velocity and normal stress, also consistent with previous studies. Our results indicate that the DDA method can well capture some of the general characteristics of shear rupture process and, hence, can be applied to study other aspects of dynamic shear ruptures. Highlights: The slip-weakening friction law is incorporated into DDA to simulate shear rupture processes along a weak interface. Under the DDA model, rupture evolution is characterized by episodic expansion and arrest, followed by a sharp transition to dynamic runaway. The DDA model reproduces a suite of shear rupture behavior, consistent with previous studies. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) is a non-destructive technique that relies on monitoring naturally occurring sources of high frequency ultrasound in components and structures. Ultrasonic waves propagate in the form of different wave modes—for instance Lamb waves in thin plates, or Rayleigh and P- and S- waves in bulk structures. Those wave modes have different properties, but also contain information regarding the source of the naturally occurring wave. Manually, the wave modes can be recognized by comparing a time–frequency representation of the signal to the dispersion curves expected in the tested object. For analyzing a large number of signals, this manual mode recognition becomes a tedious process. This paper proposes a method to automate the wave mode recognition based on some minimal knowledge of the occurring wave modes. As inputs, only the propagation speed of the possible wave modes and the source position need to be provided along with a limited set of reference wavelets for each wave mode. Cross-correlation of a signal with a reference wavelet of a mode reduces the signal to a limited number of peaks that may delineate the start of the mode. Using other signals from the same event but from different sensors, velocities are calculated for each peak in order to select the peak that corresponds to the arrival of the mode under investigation. To validate the method, a dataset was recorded based on four types of out-of-plane sources: Hsu-Nielsen sources of 0.3 and 0.5 mm, sensor pulse signals and AEs from melting ice. Since the presented dataset was recorded on a plate, the aim of the validation was to recognize the zero-order symmetrical and anti-symmetrical Lamb modes. The results of the proposed mode recognition method applied to this dataset are compared with results from manual mode recognition. For Hsu-Nielsen sources, the succes rate is found to be above 95%. For narrow-band pulsed signals or for AEs from melting ice with a low signal-to-noise ratio, succes rates between 75 and 80% relative to manual mode recognition are reported. [ABSTRACT FROM AUTHOR]

The Laguerre polynomial method has been successfully used to investigate the dynamic responses of a half-space. However, it fails to obtain the correct stress at the interfaces in a layered half-space, especially when there are significant differences in material properties. Therefore, a coupled Legendre-Laguerre polynomial method with analytical integration is proposed. The Rayleigh waves in a one-dimensional (1D) hexagonal quasicrystal (QC) layered half-space with an imperfect interface are investigated. The correctness is validated by comparison with available results. Its computation efficiency is analyzed. The dispersion curves of the phase velocity, displacement distributions, and stress distributions are illustrated. The effects of the phonon-phason coupling and imperfect interface coefficients on the wave characteristics are investigated. Some novel findings reveal that the proposed method is highly efficient for addressing the Rayleigh waves in a QC layered half-space. It can save over 99% of the computation time. This method can be expanded to investigate waves in various layered half-spaces, including earth-layered media and surface acoustic wave (SAW) devices. [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]

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]

Abstract—Ground-based magnetometers and vertical ionospheric sounding stations were used to record specific variations in the geomagnetic field, caused by the perturbation in the lower ionospheric current systems, and specific variations in the upper ionospheric electron density after a strong volcanic eruption in Kamchatka, Russia, on April 10, 2023. The analysis of the measurements from two series of explosions has shown that the impact on the lower ionosphere is realized via both seismic Rayleigh waves (which are a source of acoustic waves propagating into the ionosphere), and atmospheric internal gravity waves generated by explosions. At distances up to a thousand km from the source, a repeatability of the pattern of ionospheric perturbations after each of the six volcanic explosions is discovered. At larger distances, signals from acoustic waves caused by the Rayleigh waves are clearly recorded in the ionosphere, whereas separation of the signals from atmospheric internal waves is difficult due to the influence of perturbations from other external sources. [ABSTRACT FROM AUTHOR]

The wave reflection and transmission (R/T) coefficients in fluid-saturated porous media with the effect of effective pressure are rarely studied, despite the ubiquitous presence of in situ pressure in the subsurface Earth. To fill this knowledge gap, we derive exact R/T coefficient equations for a plane wave incident obliquely at the interface between the dissimilar pressured fluid-saturated porous half-spaces described by the theory of poro-acoustoelasticity (PAE). The central result of the classic PAE theory is first reviewed, and then a dual-porosity model is employed to generalize this theory by incorporating the impact of nonlinear crack deformation. The new velocity equations of generalized PAE theory can describe the nonlinear pressure dependence of fast P-, S- and slow P-wave velocities and have a reasonable agreement with the laboratory measurements. The general boundary conditions associated with membrane stiffness are used to yield the exact pressure-dependent wave R/T coefficient equations. We then model the impacts of effective pressure on the angle and frequency dependence of wave R/T coefficients and synthetic seismic responses in detail and compare our equations to the previously reported equations in zero-pressure case. It is inferred that the existing R/T coefficient equations for porous media may be misleading, since they lack consideration for inevitable in situ pressure effects. Modeling results also indicate that effective pressure and membrane stiffness significantly affect the amplitude variation with offset characteristics of reflected seismic signatures, which emphasizes the significance of considering the effects of both in practical applications related to the observed seismic data. By comparing the modeled R/T coefficients to the results computed with laboratory measured velocities, we preliminarily confirm the validity of our equations. Our equations and results are relevant to hydrocarbon exploration, in situ pressure detection and geofluid discrimination in high-pressure fields. [ABSTRACT FROM AUTHOR]

This paper presents a combined seismic metamaterial model based on the principle of local resonance to effectively shield Rayleigh waves at wide low-frequency bandgap in two-layered soil. In the proposed combined seismic metamaterial model, the unit-cell structure comprises two parts: a partially embedded underground concrete column and a multi-layer composite material structure enclosing the underground portion of the embedded concrete columns. By using the finite element method, the band structure and propagation characteristics of the proposed combined seismic metamaterial model are numerically investigated. Later the concrete column height effect is investigated, such as the combined seismic metamaterial model with positive gradient arrangement, negative gradient arrangement, concave arrangement, and convex arrangement. Then, the El-Centro seismic wave is considered and found that it can be considerably attenuated by the designed combined seismic metamaterial model. Additionally, this work does parameter analysis on items such as concrete density and column height. [ABSTRACT FROM AUTHOR]

The Mantle Transition Zone (MTZ) beneath the Uttarakhand Himalaya has been modelled using Common Conversion Point (CCP) stacking and depth-migration of radial P-receiver functions. In the Uttarakhand Himalaya region, the depths of the 410-km discontinuity (d410) and the 660-km discontinuity (d660) are estimated to be approximately 406 ± 8 km and 659 ± 10 km, respectively. Additionally, the thickness of the mantle transition zone (MTZ) is modelled to be 255 ± 7 km. The average arrival times for d410 and d660 conversions are (44.47 ± 1.33) s and (71.08 ± 1.29) s, respectively, indicating an undisturbed slightly deeper d410 and a deformed noticeably deeper d660 in the area. The model identifies the characteristics of the d410 and d660 mantle discontinuities beneath the Lesser Himalayan region, revealing a thickening of the MTZ towards northeast, which could be due to gradual cooling or thickening of the Indian lithosphere towards its northern limit. We simulate a low-velocity layer (perhaps partially molten) above the d410 discontinuity at depths of 350 to 385 km, indicating the presence of a hydrated MTZ beneath the area. We also interpret a negative phase at d660 as a low-velocity layer between 590 and 640 km depths, which could be attributed to the accumulation of old subducted oceanic materials or increased water content at the bottom of the MTZ. Our results suggest the presence of residues from paleo-subducted lithospheric slabs in and below the mantle transition zone underlying the Uttarakhand Himalayas. [ABSTRACT FROM AUTHOR]

This research delves into the transfer and loss of energy in a discrete mass when subjected to forced vibration. Using discrete element method (DEM), we analyzed the dynamic behavior of regular spherical granular assemblies and the energy distribution characteristics under different excitation frequencies and reduced accelerations. Moreover, the energy transfer and dissipation process of granular assemblies under different vibration states are studied using an experimental method. The results show that the granular assemblies will produce collision energy dissipation, thermal energy dissipation, acoustic energy dissipation and other forms of energy dissipation in the forced vibration state and the proportion of different energy dissipation under different excitation is given. The collision and friction of granular assemblies are the key to affecting other forms of energy dissipation. When the excitation increases, the energy dissipation forms are generated inside the granular assemblies, and the proportion of collision energy dissipation of the granular assemblies increases. The acoustic energy above 20 kHz occupies the main part of the acoustic energy dissipation. Thermal energy consumption always exists, which takes a long time to play a role. The granular also have other forms of energy loss, which is hard to be measured, including Rayleigh waves generated by granular collision. In this study, the relationship between the forced vibration state of the granular assemblies and the energy loss distribution is established. Various types of energy transfer and conversion distribution which further enriches the energy dissipation of discrete element calculation of the granular assemblies is discussed and provides a reference for the energy loss analysis of the granular assemblies. [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]

The dispersion and reflection characteristics of coupled waves in the piezomagnetic solid with flexomagnetic microstructure effect are studied in this paper. The flexomagnetic effect, strain gradient effect and micro-inertia effect are introduced into the constitutive equation and the governing equation to establish the wave propagation theory in the piezomagnetic solid with flexomagnetic microstructure effect. The secular equation of wave propagation is derived, and the properties of five coupled waves are analyzed. The dispersion characteristics of coupled waves and the reflection properties of coupled waves at the free boundary are solved numerically and checked by the energy conservation law. The influences of the flexomagnetic effect, strain gradient effect and micro-inertia effect on the wave propagation are discussed. It is found that the flexomagnetic effect mainly enhances the mechanical-magnetic coupled property, strain gradient effect mainly enhances the elastic property, and micro-inertia effect not only enhances the inertia property, but also essentially changes the dispersion characteristics of coupled waves. [ABSTRACT FROM AUTHOR]

This work analyzes the propagation of BG wave in a layered model composed of a piezo-flexo-magnetic (PFM) layer of finite width imperfectly bonded to a PFM half-space with consideration of impedance boundary at the free surface of layer. The flexo-magnetic phenomenon introduces loss which results in attenuation of propagating BG wave. Using suitable surface and interface conditions, a complex frequency equation is obtained, which relates real wave number with a complex form of wave velocity with the help of material, interface, impedance, and flexo-magnetic parameters. The dispersion and attenuation relations of BG waves are derived from separating this frequency relation into real and imaginary parts. These dispersion and attenuation equations relate wave number with phase and damp velocities, respectively. With the help of these relations, the phase/damp velocities are plotted against wave number illustrating the influence of interface imperfection parameter, the flexo-magnetic parameter corresponding to layer and half-space, impedance parameter, & layer width in magnetically short (MS) and magnetically open (MO) conditions. The impact of varying damp velocity on phase velocity and vice-versa is also portrayed in MS and MO cases. Some validation with previously existing literature is also provided. [ABSTRACT FROM AUTHOR]

The lateral impact loads induced by blasting excavation of subway tunnel are detrimental to adjacent structures with pile foundations. Physical model tests are carried out to study the dynamic behaviors and failure modes of pile foundations under blasting impact loads. Specifically, the acceleration and strain variation monitoring of friction pile foundations subjected to tunnel blasting is conducted. It is indicated that the bending moment, horizontal acceleration, and dominant frequency (DF) of the pile foundation gradually increase with the standoff distance decrease, while the vibration duration becomes shorter. In the case of pile foundations located in the far field of the explosion, an acceleration amplification effect is observed at the pile top due to the presence of Rayleigh waves (R waves) and the high-frequency filtering effect of the surrounding soil and rock mass. Consequently, the pile-superstructure system experiences resonance, leading to shear failure at the connection between the pile cap and pile top. With decreasing standoff distance, the high-magnitude blasting loads may result in either tensile failure at the pile-soil bond interface or bending failure at the connection. For the pile foundations situated in the near field of the explosion, tensile failure occurs at the pile-soil bond interface, resulting in a loss or failure of the pile's lateral frictional resistance. Alternatively, buckling failure may occur in the middle of the pile, and spalling, cracking failure of concrete occurs at the bottom of the pile. [ABSTRACT FROM AUTHOR]

This paper addresses the longstanding challenge of soft body dynamics with frictional contact through a novel combination of Projective Dynamics for elasticity simulation and Alternating Direction Method of Multipliers for frictional contact handling. The approach utilizes parallel local strain projection for deformable bodies and nonlinear Projected Gauss-Seidel for contact with Coulomb friction, consolidated by a pre-factorized global strain propagation step. Integration of contact stabilization, Matchstick anisotropic friction, and Rayleigh damping enhances reliability and usability. Effectiveness, accuracy, and computational efficiency are demonstrated in challenging cases, including multi-layer and persistent contacts. With a CPU-based parallel implementation, our method achieves visually plausible and stable simulation results at an interactive framerate in moderate-scale scenes, showcasing its applicability across various graphics applications. [ABSTRACT FROM AUTHOR]

This paper introduces a novel metasurface based on Auxetic metamaterials for attenuating and isolating low-frequency Rayleigh waves. Distributed scatterers are embedded in the Auxetic substrate to form the unit cell, and the meticulously designed layout is intended to induce more multipolar resonance modes. Firstly, the propagation characteristics of Rayleigh waves in the elastic half-space containing metamaterial domain are investigated under the dynamic effective framework of elastic media, and the effective parameter combinations for shielding Rayleigh waves are summarized, which provide a guide for customized design. Then, a new ultra-low frequency band gap is revealed via eigenstate analysis and effective parameter calculation. More noteworthy is the discovery of bridging effects in hybrid bands. Finally, multiple bandgaps, including ultra-low frequency bandgap, are integrated through hybrid bands, achieving an ultra-wide attenuation from 3.2 Hz to 20 Hz, almost perfectly covering the main frequency range of real seismic Rayleigh waves. At the same time, a reduction of up to 96.3% in the response peak is also validated in time-domain testing. More promisingly, there is still room to improve the low-frequency performance of the metasurface by optimizing the effective modulus of the Auxetic metamaterial. Undoubtedly, it further explores the physical boundary of extremely compact metamaterials in modulating even larger wavelength, which will inspire more potential Auxetic metamaterials for applications in emerging fields. [ABSTRACT FROM AUTHOR]

A SAW resonator based on langasite (LGS) substrate with (0°, 138.5°, 116.6°) cut was designed and fabricated. Simulation and experimental results demonstrate that the resonator has two resonance modes, one Rayleigh wave and the other leaky surface acoustic wave (LSAW). The temperature dependent resonance frequencies of both Rayleigh wave and LSAW had been studied. The results show that the turnover temperature of LSAW mode is below absolute zero, namely, the resonance frequency of LSAW changes monotonically in rather wide temperature range, such as from cryogenic to ultrahigh temperatures. Real-time temperature measurement shows that the temperature sensor based on the LSAW mode can effectively monitor the environment temperature, as the thermocouple does. Our work suggests that the LSAW temperature sensor has great application potential in aerospace field for wide temperature range sensing. [ABSTRACT FROM AUTHOR]

The rheological models of Lomnitz and Jeffreys have been widely used in earthquake seismology (to simulate a nearly constant Q medium) and to describe the creep and relaxation behavior of rocks as a function of time. Other similar models, such as those of Becker, Scott Blair and Kolsky, show similar properties, particularly the Scott Blair model describes a perfectly constant Q as a function of frequency. We first give a historical overview of the main scientists and the development and versions of the various models and priorities of discovery. Then, we clarify the relationship between the different versions of these models in terms of mathematical expressions of the complex modulus and calculate the phase velocity and quality factor Q as a function of frequency, illustrating the various special cases. In addition, we give useful hints for the numerical calculation of these moduli, which include special cases of the hypergeometric function. [ABSTRACT FROM AUTHOR]

Rayleigh wave exploration is a powerful method for estimating near-surface shear-wave (S-wave) velocities, providing valuable insights into the stiffness properties of subsurface materials inside the Earth. The dispersion curve inversion of Rayleigh wave corresponds to the optimization process of searching for the optimal solutions of earth model parameters based on the measured dispersion curves. At present, diversified inversion algorithms have been introduced into the process of Rayleigh wave inversion. However, limited studies have been conducted to uncover the variations in inversion performance among commonly used inversion algorithms. To obtain a comprehensive understanding of the optimization performance of these inversion algorithms, we systematically investigate and quantitatively assess the inversion performance of two bionic algorithms, two probabilistic algorithms, a gradient-based algorithm, and two neural network algorithms. The evaluation indices include the computational cost, accuracy, stability, generalization ability, noise effects, and field data processing capability. It is found that the Bound-constrained limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS-B) algorithm and the broad learning (BL) network have the lowest computational cost among candidate algorithms. Furthermore, the transitional Markov Chain Monte Carlo algorithm, deep learning (DL) network, and BL network outperform the other four algorithms regarding accuracy, stability, resistance to noise effects, and capability to process field data. The DL and BL networks demonstrate the highest level of generalization compared to the other algorithms. The comparison results reveal the variations in candidate algorithms for the inversion task, causing a clear understanding of the inversion performance of candidate algorithms. This study can promote the S-wave velocity estimation by Rayleigh wave inversion. [ABSTRACT FROM AUTHOR]

In this paper, a novel silicon nanoparticle-based sensor has been investigated. Bloch surface wave excitation in a one-dimensional photonic crystal using a silicon nanoparticle on the top defect layer is examined on various parameters. This paper compares the confinement of Bloch surface wave using with and without silicon nanoparticles. The confinement of surface waves is modified by varying the size of the silicon nanoparticle. The structural parameters are optimized for an 850 nm (nm) central wavelength. At the central wavelength of 850 nm, the confinement of surface waves gets modified by varying the size of the silicon nanoparticle. The proposed novel silicon nanoparticle-based sensor was investigated and its efficacy in terms of sensitivity, quality factor, and Figure of merit was evaluated. The sensitivity is demonstrated to be 148.88 Degree/Refractive index unit (RIU), with a quality factor of 10,146.83 nm and a figure of merit (FOM) of 1777.24 per Refractive index unit (RIU− 1) for sensors with a silicon nanoparticle-based multilayer structure. [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]

Rayleigh-type surface waves propagating in a magneto-elastic half-space containing voids are studied. Dispersion equation is derived under suitably constructed boundary conditions, which involves elastic, electro-magnetic, void parameters and angular frequency, but contains radicals, making it difficult to solve analytically. However, under limiting frequencies, the dispersion equation is analyzed and discussed. The effect of various parameters on phase velocity of propagating Rayleigh-type surface waves is investigated and shown graphically for a particular model. The effect of induced electric field on considered surface waves is also studied and explained. It is shown that the particles near the boundary surface move in an elliptic manner. However, if there is no phase difference between the displacement components, then we have a degenerate case. Some special cases of dispersion relation are also deduced from the present formulation. [ABSTRACT FROM AUTHOR]

In the present investigation, the scattering nature of SH-waves in the irregular free surface of a linear orthotropic viscoelastic layer lying over orthotropic viscoelastic half-space has been considered. Different types of surface irregularity viz. parabolic type, rectangular type, and triangular notch type have been taken into account in the aforesaid structure. The closed-form expressions of dispersion as well as damping relations have been deduced analytically. The expressions for the induced reflected displacement due to scattering phenomena of SH-waves have also been deduced for all aforesaid cases of surface irregularity. The effects of the anisotropy parameter of the upper layer on the phase velocity and the attenuation coefficient of scattered SH-waves have also been examined. The effects of vertical irregularity parameter and anisotropy parameter on the induced reflected displacement component have also been examined. Further, a comparative observation has also been outlined and discussed. [ABSTRACT FROM AUTHOR]

Intracrustal low-velocity zones (LVZs) indicate a mechanically weak crust and are widely observed in the southeast margin of the Tibetan Plateau. However, their spatial distributions and formation mechanisms remain controversial. To investigate their distribution and detailed morphology of the LVZs in the southeastern Tibetan Plateau, here we used teleseismic events and continuous waveform data recorded by 40 broadband seismic stations newly deployed in the Sichuan-Yunnan region from December 2018 to October 2020. A total of 12,924 high-quality P-wave receiver functions and 5–40 s fundamental Rayleigh surface wave phase velocity dispersion curves from ambient noise cross-correlation functions were obtained. The S-wave velocity model at a depth interval of 0–100 km in the study area was inverted by using the trans-dimensional Markov chain Monte Carlo strategy to jointly invert the complementary data of the receiver function waveform and Rayleigh surface wave phase velocity dispersion. Our results show that there are two separate LVZs (∼3.5 km/s) surrounding the rigid Daliangshan subblock at crustal depths of approximately 30–40 km, providing new constraints on the geometry of the LVZs in our study region. The two LVZs obtained in this study may represent the middle crustal flow channels, through which the material in the center of the Tibetan Plateau extrudes to its southeast margin. Blocked by the rigid Sichuan Basin and the spindle-like Daliangshan subblock, the material continues to flow southward through the mechanically weak middle crustal channels surrounding the Daliangshan subblock. In addition, the existence of thin LVZs in the middle crust plays an important role in understanding the decoupling between the upper and lower crust in the study area. It also provides new constraint on the complex tectonic deformation process of the southeastern margin of the Tibetan Plateau caused by the collision and compression of the Indian and the Eurasian plates. [ABSTRACT FROM AUTHOR]

The primary purpose of this study is to develop an asymptotic formulation for boundary value problems in a non-local elastic half-space. For the sake of simplicity, the non-locality is limited to the vertical direction, which is represented by a one-dimensional exponential kernel, and the problem is formulated within the framework of Eringen's theory. The proposed asymptotic approach is based on the assumption that the internal characteristic length is significantly smaller than a typical wavelength. This assumption allows for the development of an asymptotic formulation that expresses the considered boundary value problem in terms of local stresses. Additionally, the formulation includes explicit correction terms to the classical boundary conditions, which arise from the non-local effects. As an example application of the derived formulation, the Rayleigh surface waves in a plane strain problem are considered. Finally, numerical results are presented for certain specific values of elastic parameters to illustrate the effects of non-locality on the analyzed system. [ABSTRACT FROM AUTHOR]

We determined the velocity structure of the upper crust in the Jiaodong area using double difference seismic tomography, and found that the Jiaodong inland area near the surface (0–5 km) is mainly characterized by high-velocity anomaly, and there are several obvious low-velocity anomalies in the Bohai Sea. The Queshan metamorphic core complex shows obvious low-velocity anomaly at the depth of 5–15 km, and the southern part of the Linglong shows low-velocity anomaly at the depth of 10–20 km. It indicates the existence of significant mantle material upwelling and magmatic activity beneath metamorphic core complex. The Linglong and Queshan metamorphic core complex may be still in the process of uplift. The high-velocity anomaly of the Wulian-Yantai fault is likely closely related to the basic to ultrabasic rocks from the mantle. The basic to ultrabasic rocks upwelling along the Wulian-Yantai fault zone is segmented and mainly concentrated in the southern of the fault zone. [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 tomography results reveal not only distinct velocity structures in different tectonic zones but can also provide valuable insights into the geological features of the area. This study presents the results of 2D Rayleigh wave tomographic maps obtained in NE Iran. For this purpose, we used the recorded waveforms of more than 500 earthquakes with M > 4 that occurred between January 2000 and October 2020 at 165 stations. The calculated tomographic maps cover a period range of 3 to 36 s, providing the 3D VS model to analyze crustal structure at depths ranging from 2 to 30 km. At shorter periods, the tomographic maps are primarily influenced by sediment thickness, with the presence of thick sediment layers (~ 10 km) responsible for the observed low VS anomalies (< 3.1 km/s) in the study area. At longer periods, the tomographic maps highlight the structural characteristics of the middle-lower crustal layers and, somewhere, the depth variations of the Moho discontinuity. The VS model also confirms the correlation between tectonic fractures and known faults in the study area as boundaries of seismotectonic provinces. Moreover, a distinct area was observed beneath the Binalud foreland, which we interpreted as a suture zone, as suggested by previous studies. The reliability of the resolved anomalies was supported through a series of tests, including checkerboard and earthquake location uncertainties. These tests demonstrated the robustness of the results and provided confidence in the accuracy of the findings. [ABSTRACT FROM AUTHOR]

A series of models based on the finite element method (FEM) for analyzing the parameters of surface acoustic waves (SAWs) and devices based on them are described. The computer method for generating models in the COMSOL Multiphysics program is described in a generalized form. The work in three main solvers in the COMSOL environment—the stationary mode, eigenfrequency domain, and frequency domain—is described and graphically illustrated. The properties of Rayleigh waves and leaky SAWs are analyzed. A visualization of a number of characteristics is presented. The analysis of parameters such as the phase velocity of the wave, electromechanical coupling coefficient, and static capacitance of the transducer is considered. The examples consider an equidistant transducer, a transducer with split electrodes, and a unidirectional transducer of the DART type. Methods for analyzing harmonics in SAWs and the waveguide effect are proposed. It is shown that the model is valid for both single-crystal substrates and layered structures. The analysis of the temperature coefficient of the frequency for structures as such TCSAW (temperature-compensated SAW) and I.H.P.SAW (incredible high-performance SAW) is considered. A model for calculating the amplitude-frequency responses of devices is presented. It is shown that the data obtained as a result of the numerical analysis correspond to the experimental data and known published sources. [ABSTRACT FROM AUTHOR]

The present article focuses on the Rayleigh surface wave propagation in homogeneous isotropic thermoelastic medium. This works aims to develop a new nonlocal elasticity model based on three-phase-lag model of hyperbolic thermoelasticity under double porosity structure. New constitutive relations and equations are derived using nonlocal continuum mechanics. State space approach is employed to solve the problem. Frequency equation is derived using appropriate boundary conditions. Path of surface particles is found elliptical at the time of Rayleigh surface wave propagation. Different characteristics of Rayleigh waves are calculated numerically and presented graphically for different wave number. Various characteristics of wave for different thermoelastic models are also presented graphically. The effect of nonlocal parameters and void parameters on phase velocity, attenuation coefficient, penetration depth, and specific loss of Rayleigh waves are shown graphically. Some special cases are deduced from this study which agree with the existing literatures. [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]

The article is focused on the analysis of a mathematical model known as the Nizhnik–Novikov–Veselov (SNNV) system, which incorporates a specialized mathematical tool called the truncated M-fractional derivative (TMD). This model has broad applications in various scientific fields and considered an isotropic Lax extension of the one-dimensional Kdv equation which has diverse applications in the areas of warm ions, shallow water waves, electromagnetic signals, and river irrigation flows. To extract the solutions of the SNNV system, a modified version of the extended tanh-function method which is known as amended extended tanh-function method (AETF) is brought into play to derive solitary wave solutions for the SNNV system. These formulated solutions are categorized as trigonometric, exponential, and hyperbolic functions. For physical exemplification and knowledge of the dynamic physical features of the governing model, some reported solutions have been deliberated graphically by selecting appropriate parametric values. The computed outcomes have implications in diverse areas of applied sciences such as quantum mechanics, magneto-electrodynamics, heavy ion collisions, optical fiber technology and also opens doors to practical applications in diverse domains. The application of the AETF approach in this study demonstrates its efficiency and competence in scrutinizing and extracting soliton solutions in nonlinear partial differential equation. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions have great potential for developing novel spintronic devices. The electrical manipulation of skyrmions has mainly relied on current-induced spin-orbit torques. Recently, it was suggested that the skyrmions could be more efficiently manipulated by surface acoustic waves (SAWs), an elastic wave that can couple with magnetic moment via the magnetoelastic effect. Here, by designing on-chip piezoelectric transducers that produce propagating SAW pulses, we experimentally demonstrate the directional motion of Néel-type skyrmions in Ta/CoFeB/MgO/Ta multilayers. We find that the shear horizontal wave effectively drives the motion of skyrmions, whereas the elastic wave with longitudinal and shear vertical displacements (Rayleigh wave) cannot produce the motion of skyrmions. A longitudinal motion along the SAW propagation direction and a transverse motion due to topological charge are simultaneously observed and further confirmed by our micromagnetic simulations. This work demonstrates that acoustic waves could be another promising approach for manipulating skyrmions, which could offer new opportunities for ultra-low power skyrmionics. Skyrmions, a type of topological spin texture, have garnered interest for use in spintronic devices. Typically, these devices necessitate moving the skyrmions via applied currents. Here, Yang et al demonstrate the driving of skyrmions by surface acoustic waves. [ABSTRACT FROM AUTHOR]

Disturbances in the lower ionosphere and in the region of the maximum of the ionospheric F2 layer during the eruption of Shiveluch volcano in April 2023 are analyzed based on data from ground-based magnetometers and GPS radio sounding of the ionosphere. The magnetic stations were located at distances of 455 (Paratunka) and 752 km (Magadan) from the volcano. The variations in the magnetic field and total electron content of the ionosphere were studied as characteristics of the ionospheric response to this event. Analysis of the measurements showed that the ionosphere was impacted by seismic Rayleigh waves and atmospheric acoustic-gravity waves generated by volcanic explosions. The energy of several explosions was estimated from the amplitude of the ionospheric signal in the total electron content. [ABSTRACT FROM AUTHOR]

A theoretical and experimental study was conducted to investigate the effect of injection angle on surface waves. Linear stability theory was utilized to obtain the analytical relation. In the experimental study, high-speed photography and shadowgraph techniques were used. Image processing codes were developed to extract information from photos. The results obtained from the theoretical relation were validated with the experimental results at different injection angles. In addition, at the injection angle of 90 ∘ , the theoretical results were evaluated with the experimental results of other researchers. This evaluation showed that the theory results were in good agreement with the experimental data. The proper orthogonal decomposition (POD) and the power spectra density (PSD) analysis were also used to investigate the effect of the injection angle on the flow structures. The results obtained from the linear stability were used to determine the maximum waves' growth rate, and a relation was presented for the breakup length of the liquid jet at different injection angles. The breakup length results were compared with theory and published experimental data. The presented relation is more consistent with experimental data than other theories due to considering the nature of waves. The results showed that the instability of the liquid jet is influenced by three forces: inertial, surface tension, and aerodynamic. Therefore, Rayleigh–Taylor, Kelvin–Helmholtz, Rayleigh–Plateau, and azimuthal instabilities occur in the process. Decreasing the injection angle changes the nature of waves and shifts from Rayleigh–Taylor to Kelvin–Helmholtz. That reduces the wavelength and increases the growth rate of the waves. Axial waves have a significant impact on the physics of the waves and influence parameters. If axial waves are not formed, the growth rate of the waves is independent of the injection angle. An increase in the gas Weber number causes a change in the type of dominant waves and a greater instability of the liquid jet. In contrast, an increase in the liquid Weber number causes an enhancement in the resistance of the liquid jet against the transverse flow without changing the type of the dominant waves. Decreasing the density ratio reduces the effect of Rayleigh–Taylor waves and strengthens the Kelvin–Helmholtz waves. It causes two trends to be observed for the growth rate of waves at low spray angles, while one trend occurs at high spray angles. [ABSTRACT FROM AUTHOR]

Location of damage sources is an important aspect of structural health monitoring research. Acoustic emission (AE) technology is broadly concerned due to its potential advantages in damage monitoring and source localization. However, the traditional positioning method is based on the arrival of P wave, and the non-uniformity of concrete materials is not considered, resulting in poor accuracy at large distances. This paper describes a non-contact AE localization method using leaky Rayleigh waves via a new air-coupled MEMS microphones array unit. Compared with traditional contact detection, this method is convenient for rapid setup and monitoring in a wider range. The feasibility of the non-contact AE localization method was verified by numerical simulation and experiments. Azimuth (direction of arrival) of AE source is a key source parameter for damage location. The research shows that this method can determine the azimuth of AE source at different positions, the results are close to the actual coordinates. Non-contact monitoring method proposed in this paper is the basis for further research on the failure prediction of concrete plate-like structures such as tunnel lining and bridge deck. [ABSTRACT FROM AUTHOR]

Purpose: The objective of present work is to investigate seismic wave reflection/transmission in an orthotropic layer bonded between two piezoelectric half-spaces in presence of an imperfect corrugated superstratum and sliding lower interface. Methods: Closed form analytical expressions for displacement field, electric potential, and velocity profile of quasi seismic waves are deduced for respective geomedia using time harmonic plane wave solution approach with appropriate boundary conditions. Rayleigh's first-order approximation, generalized Snell's law and spectrum theorem are used to determine the analytical solution for reflection, transmission (RT) coefficients for regularly and irregularly scattered waves. Results: Numerical simulations for specific geophysical model have been carried out and results are presented through multiple plots to analyze the impact of incident angle, dimensionless layer width, sliding parameter, and corrugated boundary on resultant velocity profile and RT coefficients. The energy flux ratios of all regularly and irregularly propagating waves are also analyzed and portrayed against angle of incidence (AOI). Conclusions: Reflection and transmission angle for all the quasi-waves are found monotonically increasing with rise in incident angle. Waves and material parameters are found to have different impact on resultant velocity and RT coefficients. Simulation also reveals the effect of two extrema of sliding parameter corresponding to welded and free contact on RT coefficients. The coefficients obtained by first-order approximation to corrugation are found to have proportional impact of corrugation amplitude. [ABSTRACT FROM AUTHOR]

Field observations proved that tensile branches can be formed during fault growing and contribute with other types of fractures in creating a fractured zone around dynamic faults. In this study, the effects of rupture speed (c), initial stress ratio (σxxo/σyyo), and residual strength ratio (τr/τp) on the preferred direction of tensile branches around the main fault plane were investigated using the maximum tangential stress criterion (MTS-Criterion). The slip weakening model was used to regularize shear stress between fault surfaces. The analytical model indicated that tensile branches can grow through acute or obtuse angles in forward or backward directions in the extensional side of the fault, respectively. The low values of branching angle are accompanied by a high residual strength ratio, and vice versa for high values of branching angle. For rupture speeds less than 0.9 of the Rayleigh wave speed, the preferred direction of the new tensile branch is initially a function of the initial stress ratio, residual strength ratio and rupture speed. While for rupture speeds near the limiting velocity (χcr between 0.9 and 1.0), the preferred direction for the new tensile branch is independent of the initial stress state and residual strength ratio, and it is mainly a function of the rupture speed. The application of the preferred direction of tensile branches in geological and geophysical field was discussed and some field examples were shown here to validate the results of this study. [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]

The problem of the electromagnetic radiation interaction with a semiconductor nanolayer has been solved. The nanolayer thickness can be comparable to or less than the charge carrier de Broglie wavelength. The isoenergy surface has the shape of an ellipsoid of revolution. We assume the constant energy ellipsoid rotation axis lies in the nanolayer plane and is directed to the electric field intensity vector at an arbitrary angle. Analytical expressions are derived for the polarization characteristics of reflected and transmitted waves: the ellipticity coefficient and the inclination angle of the polarization ellipse major axis. Optical coefficients are calculated. We obtained the results for the limiting cases of degenerate and nondegenerate electron gas. We analyzed the dependences of the reflected wave polarization parameters and optical coefficients on the dimensionless semiconductor nanolayer thickness, the electromagnetic wave frequency, the chemical potential, the isoenergy surface anisotropy parameter, the insulating media dielectric constants and the roughness parameters of semiconductor nanolayer surfaces. [ABSTRACT FROM AUTHOR]

The paper considers the problem about mathematical modeling of internal gravity waves in ocean of finite depth with an arbitrary distribution of buoyancy frequency excited by moving perturbation source. In the linear formulation, the main dispersion characteristics determining the properties of excited far wave fields are analytically and numerically investigated. It is shown that far wave fields of an individual mode is a sum of separate wave packages. The phase and amplitude structures of far fields of internal gravity waves from moving perturbation sources are numerically investigated for various modes of wave generation. [ABSTRACT FROM AUTHOR]

We study the anelastic properties (attenuation and velocity dispersion) of surface waves at an interface between a finite water layer and a porous medium described by Biot theory including the frequency-dependent effects due to mesoscopic flow. A closed-form dispersion equation is derived, based on potential functions and open and sealed boundary conditions (BC) at the interface. The analysis indicates the existence of high-order surface modes for both BCs and a slow true surface mode only for sealed BC. The formulation reduces to two particular cases in the absence of water and with infinite-thickness water layer, with the presence of pseudo-versions of Rayleigh and Stoneley waves. The mesoscopic flow affects the propagation of all the pseudo-surface waves, causing significant velocity dispersion and attenuation, whereas the effect of the BC is mainly evident at high frequencies, due to the presence of the slow Biot wave. The mesoscopic-flow peak moves to low frequencies as the thickness of the water layer increases. In all cases, the true surface wave resembles the slow P2 wave, and is hardly affected by the flow. [ABSTRACT FROM AUTHOR]

Abstract—Ground-based magnetometers and ionospheric radio probing by means of GPS were used to analyze and interpret specific variations of the geomagnetic field and the total electron content of the ionosphere during strong catastrophic earthquakes in Turkey on February 6, 2023. It is shown that the ionospheric responses to these earthquakes recorded at distances of 1200–1600 km from the epicenter in the lower ionosphere and at distances of up to 500 km from the epicenter in the upper ionosphere can be interpreted in terms of the propagation of the Rayleigh seismic wave and atmospheric waves—shock, acoustic and internal, that is, those waves that are generated by the earthquake itself. The energy of seismic events was estimated from the ionospheric response. [ABSTRACT FROM AUTHOR]

Rayleigh wave group velocity dispersion data of moderate magnitude (Mw 5.4) earthquake of Assam, North-East (NE) India, is used to retrieve regional shear wave crustal velocity models. The earthquake located within the northeast part of the Indian continent is well recorded by 10 broadband seismic stations situated on the Indian, Eurasian, and Burmese plates to generate excellent Rayleigh waveforms. Wave propagation paths transverse different geotectonic units in the collision zones of India–Eurasia and India–Burmese in and around NE India. We divide the data into outer and inner station groups depending on epicentre distance. Paths of the inner group mainly pass through the Indian plate, and the outer group crosses the inter-continent zones. The dispersion data and corresponding shear wave structure are not dependent on group division or epicentre distance, indicating diversity in the tectonic and geological setup. Paths crossing the Bengal basin (BB) with thick sediment layers have low velocities, and older crystalline rocks of the Shillong Plateau and Himalayan region have high velocities in the uppermost 10–15 km crust. A very high contrast of crustal velocity is noticed along the paths of Agartala (AGART) and Dhubri (DHUB) stations located at similar epicentre distances and an azimuthal difference of only 55°. Path to AGART along the BB has very low crustal velocities, while DHUB along the entire Shillong Plateau region has very high velocities. Four stations of the inner group within the Indian plate have a high difference in crustal velocities: low velocities within thick sediments of BB and high velocities in the older crystalline rocks of the Shillong plateau. In contrast, in the northern part of the Indo-Burma subduction zone, the subsurface structure shows repeated underthrusting of low-velocity material from the down-going plate and over-thrusting of high-velocity material from the overriding plate. [ABSTRACT FROM AUTHOR]

Between 2017 and 2019, the CSIR-NGRI, Hyderabad, Telangana, established a broad-band seismic-network with fifty-five 3-component broadband seismometers in the Himalayan region of Uttarakhand, India. Out of 55 three component broadband seismic (BBS) networks, we chose 17 for the present study. Using digital waveform data from twenty-one (21) regional Indian earthquakes of Mw 5.0–6.2 that were recorded in the 17 broadband seismometer, we compute fundamental mode group-velocity dispersion (FMGVD) characteristics of surface waves (Love and Rayleigh waves) and the average one-dimensional regional shear-wave velocity (Vs) structure of the Uttarakhand Himalayan region. First, we compute FMGVD curves for Love waves (6–73 s) and Rayleigh waves (at 6.55–73 s) period, and then, we finally invert these dispersion curves to compute the final average one-dimensional regional crustal & sub-crustal shear-wave velocity (Vs) structure below the Uttarakhand Himalaya. Our best model in Uttarakhand Himalayan region, India, reveals the 8-layered crust with a mid-crustal low velocity layer (MC-LVL) (approximately a drop of 1.5–2.3% in Vs) between 8 and 20 km depth in the proximity of MCT (Main Central Thrust). In the upper crustal part (0–20 km depths), our modelling suggests shear velocities (Vs) varies from 3.1 to 3.9 km/sec while shear velocities (Vs) in the lower crustal part (20–45 km depth) are modelled to be varying from 3.7 to 4.69 km per sec. The Moho-depth is calculated to be 45 km deep below the K-G Himalaya, and the shear-velocity (Vs) in the sub-crustal sector is 4.69 km/sec. Our estimated mid-crustal low-velocity layer (MC-LVL) could be linked to the presence of metamorphic fluids in the fractured Main Himalayan Thrust (MHT), resulting from the weakening of the crustal material at the interface between the overriding Eurasian plate and upper part of the underthrusting Indian plate. [ABSTRACT FROM AUTHOR]

Previous literature has highlighted the importance of maternal behavior during the prenatal period for the upbringing of healthy adults. During pregnancy, fetal health assessments are mainly carried out non-invasively by monitoring fetal growth and heart rate (HR) or RR interval (RRI). Despite this, research entailing prediction of fHRs from mHRs is scarce mainly due to the difficulty in non-invasive measurements of fetal electrocardiogram (fECG). Also, so far, it is unknown how mHRs are associated with fHR over the short term. In this study, we used two machine learning models, support vector regression (SVR) and random forest (RF), for predicting average fetal RRI (fRRI). The predicted fRRI values were compared with actual fRRI values calculated from non-invasive fECG. fRRI was predicted from 13 maternal features that consisted of age, weight, and non-invasive ECG-derived parameters that included HR variability (HRV) and R wave amplitude variability. 156 records were used for training the models and the results showed that the SVR model outperformed the RF model with a root mean square error (RMSE) of 29 ms and an average error percentage (< 5%). Correlation analysis between predicted and actual fRRI values showed that the Spearman coefficient for the SVR and RF models were 0.31 (P < 0.001) and 0.19 (P < 0.05), respectively. The SVR model was further used to predict fRRI of 14 subjects who were not included in the training. The latter prediction results showed that individual error percentages were (≤ 5%) except in 3 subjects. The results of this study show that maternal factors can be potentially used for the assessment of fetal well-being based on fetal HR or RRI. [ABSTRACT FROM AUTHOR]