Surface Wave Velocity Research Articles

Hydraulic jumps in inhomogeneous strongly coupled toroidal dust flows

The inhomogeneous flow of strongly coupled dust particles in a toroidal particle trap with harmonic radial confinement is analyzed in the incompressible fluid limit. It is shown that the flow can spontaneously generate shock-like events, which are similar to the hydraulic jump in open channel flows. A definition of the Froude number for this model is given and the critical speed is recovered as the group velocity of surface waves. This hydraulic model is compared with molecular-dynamics simulations, which show that a sudden bifurcation of the flow lines and a localized temperature peak appear just at the point where the critical condition for the hydraulic jump is located.

Surface Waves in a Viscoelastic Liquid Half-Space Under Initial Stress in Presence of Thermal and Magnetic Field

In this paper propagation of Rayleigh-type surface waves in a homogeneous, isotropic, perfectly conducting viscoelastic liquid half-space under initial stress in presence of thermal and magnetic field has been discussed, in the context of generalized thermoelasticity using Green–Lindsay model. The frequency equation signifying the velocity of Rayleigh surface waves has been established. The velocity of Rayleigh surface waves is computed numerically for different values of initial stress parameter, magnetic pressure number, thermoelastic coupling parameter and viscosity. The results are shown graphically.

Rayleigh wave dispersion in an irregular sandy Earth's crust over orthotropic mantle

The present paper presents a study of Rayleigh wave propagation in a sandy crustal layer of the Earth lying over an orthotropic mantle with irregular boundary surfaces under the influence of initial stress, gravity field and rigid boundary plane. An attempt has been made to study the dynamics of the individual medium and derive the displacement of the wave for both the media separately. Suitable boundary conditions have been imposed to derive the dispersion equation in closed form. In general, the obtained dispersion equation is complex, which on separating into real and imaginary parts, leads to two different dispersion equations, of which we are neglecting the imaginary part being damping in nature. The real part contains complete information regarding corrugation parameter, wave number, phase velocity, sandy parameter, initial stress and gravity field. The results for irregular boundaries have been obtained in three cases and presented using graphs. It has been found that the initial stress and sandy parameter have a significant effect and remarkable bearing on the phase velocity of Rayleigh surface wave. Corrugation parameters also have a dominant impact on the propagation of Rayleigh wave. This study may be of great help in the field of industrial engineering, submarine structures, civil engineering, aerospace, chemical pipe and metallurgy as well as geophysics.

Surface acoustic wave velocity and elastic constants of cubic GaN

We present high-resolution surface Brillouin scattering measurements on cubic GaN layers grown on GaAs substrate. By using a suitable scattering geometry, scattering by surface acoustic waves is recorded for different azimuthal angles, and the surface acoustic wave velocities are determined. A comparison of experimental results with numerical simulations of the azimuthal dependence of the surface wave velocity shows good agreement and allows a consistent set of elastic constants for c-GaN to be determined.

Near-surface fault detection by migrating back-scattered surface waves with and without velocity profiles

We demonstrate that diffraction stack migration can be used to discover the distribution of near-surface faults. The methodology is based on the assumption that near-surface faults generate detectable back-scattered surface waves from impinging surface waves. We first isolate the back-scattered surface waves by muting or FK filtering, and then migrate them by diffraction migration using the surface wave velocity as the migration velocity. Instead of summing events along trial quasi-hyperbolas, surface wave migration sums events along trial quasi-linear trajectories that correspond to the moveout of back-scattered surface waves. We have also proposed a natural migration method that utilizes the intrinsic traveltime property of the direct and the back-scattered waves at faults. For the synthetic data sets and the land data collected in Aqaba, where surface wave velocity has unexpected perturbations, we migrate the back-scattered surface waves with both predicted velocity profiles and natural Green's function without velocity information. Because the latter approach avoids the need for an accurate velocity model in event summation, both the prestack and stacked migration images show competitive quality. Results with both synthetic data and field records validate the feasibility of this method. We believe applying this method to global or passive seismic data can open new opportunities in unveiling tectonic features.

Velocity measurements of cylindrical surface waves with a large aperture line-focus acoustic transducer

Acoustic microscopy has been widely applied in the measurements of the mechanical properties. However, the measurement of wave velocity on a curved cylindrical surface by acoustic microscopy was seldom reported. In this paper, we adopted a large aperture line-focus PVDF transducer and a defocusing measurement system to measure the velocity of a cylindrical surface waves. The theoretical model was established to study the relationship among the propagation path of surface waves, the geometric parameters of a transducer, and the diameter of a shaft specimen. Based on theoretical deduction and mathematical modeling, theoretical oscillation curves of phase difference were obtained. According to the improved V(f,z) analysis method, the V(f,z) curves were obtained through analyzing experimental data at different frequencies by Fourier transform. Then the surface wave velocity of the cylindrical tungsten steel specimen (Ø 20mm) could be determined by fitting the V(f,z) curves with the theoretical curves. The measurement results were consistent with the theoretical values, indicating that the measurement method was feasible. This study laid the basis for the ultrasonic measurement of the mechanical properties on the layer-coated cylinders.

Time-lapse monitoring of internal erosion in earthen dams and levees using ambient seismic noise

Earthen dams and levees are prone to progressive failure through internal erosion of their structure. Internal erosion is often invisible to current methods of inspection until it manifests itself at the exterior surface. This study focuses on the novel use of passive seismic interferometry to monitor temporal changes in earthen embankments caused by internal erosion. This technique uses the ambient seismic noise – i.e. ambient vibrations – propagating through the structure. Laboratory-scale and field-scale embankment failure experiments are monitored. Seismic impulse responses are reconstructed from the ambient noise and temporal variations in seismic wave velocities are observed throughout each test. The application of seismic interferometry on a canal embankment tested to failure by internal erosion revealed up to 20% reductions in surface wave velocity as internal erosion progressed. The monitoring of a field embankment loaded to partial failure revealed a 30% reduction in averaged surface wave velocity. Some local velocity variations showed good agreement with local pore water pressure responses.

Ultrasound Velocity Measurements in High-Chromium Steel Under Plastic Deformation

In the present study, the variation of the propagation velocity of ultrasound in the plastic deformation of corrosion-resistant high-chromium steel 40X13 with ferrite-carbide (delivery status), martensitic (quenched) and sorbitol (after high-temperature tempering) structures have beem studied/ It is found that each state shows its view of the loading curve. In the delivery state diagram loading is substantially parabolic throughout, while in the martensitic state contains only linear strain hardening step and in the sorbitol state the plastic flow curve is three-step. The velocity of ultrasonic surface waves (Rayleigh waves) was measured simultaneously with the registration of the loading curve in the investigated steel in tension. It is shown that the dependence of the velocity of ultrasound in active loading is determined by the law of plastic flow, that is, the staging of the corresponding diagram of loading. Structural state of the investigated steel is not only changing the type of the deformation curve under uniaxial tension, but also changes the nature of ultrasound speed of deformation.

Thermal structure and melting conditions in the mantle beneath the Basin and Range province from seismology and petrology

AbstractTo better constrain the temperature structure in the upper mantle, we jointly invert seismic surface wave velocities and basalt thermobarometry. New measurements of the water concentration (1.0–3.5 wt %) and oxygen fugacity (FMQ + 0.5 to + 1.5) of basalts from seven recently active volcanic fields in the Basin and Range province (Cima, Pisgah, Amboy, Big Pine, Black Rock, Snow Canyon, W. Grand Canyon) enable more accurate equilibration pressure (P) and temperature (T) estimates of the mantle melts. We developed a revised thermobarometer that more precisely predicts the results of laboratory experiments on melts equilibrated with olivine and orthopyroxene and accounts for the effects of water and CO2. Applying these methods to basalts from the Basin and Range we find that most equilibrated near the dry solidus in P‐T space and at depths in the vicinity of the lithosphere‐asthenosphere boundary (LAB) inferred from receiver function analysis and Rayleigh surface wave tomography. The wet basalts should have begun melting well below the dry solidus, so the depths of equilibration probably reflect ponding of rising melts beneath the nominally dry lithosphere. A two‐parameter thermal model is sufficient to simultaneously satisfy both the seismological and petrological constraints. In the model, the depth to the dry solidus defines the bottom boundary of the conductive lid, while the potential temperature (Tp) controls the asthenosphere and LAB thermal structure. The optimum estimates of Tp range from <1300 to >1500°C, and depths to the LAB range from ∼55 to 75 km, with uncertainties on the order of ±50°C and ±10 km. In contrast to standard tomographic images or basalt thermobarometry, the output of the joint inversion is a geotherm that can be tested quantitatively against other observations.

Theoretical Analysis of SAW Propagation in 3C-SiC/c-AlN

The anisotropic materials as the acoustic wave propagating medium introduce the dependence of the phase velocity on the wave propagation direction, as opposed to the isotropic counterparts; in addition, the profile of the particle displacement components can be quite different, depending on the crystal type and propagation direction. The propagation of surface and bulk acoustic waves (SAWs and BAWs) along the (001), (111) and (110) planes of cubic SiC crystals have been studied. For specific propagation directions in these planes, slight variations in the velocity of the elastic surface waves are found. It was observed that Rayleigh-type, generalized and pseudo-surface waves can propagate at specific directions, thus confirming how the anisotropic behavior of the bare SiC substrate modifies the existence and the field profile of the SAW that propagates at its free surface. Finally, the SAW propagation along AlN/SiC-based multilayered structures is studied for the three SiC planes, different AlN piezoelectric layer thicknesses and electrical boundary conditions.

Effect of loosely bonded undulated boundary surfaces of doubly layered half-space on the propagation of torsional wave

This paper investigates the propagation of torsional wave in an initially stressed poroelastic layer with corrugated as well as loosely bonded boundary surfaces, sandwiched between a corrugated fiber-reinforced layer and a viscoelastic half-space under initial stress. The velocity equation has been obtained in closed form analytically and the substantial effect of affecting parameters on the phase velocity of torsional surface wave has been demonstrated numerically and graphically. Comparative study has been made to observe the effect of flatness parameter, reinforcement, viscoelasticity and porosity on the phase velocity, meticulously. Some particular cases have also been discussed and it is found that velocity equation is in well-agreement to the classical Love wave equation. Moreover, some remarkable observation has been made through numerical computation and graphical demonstration for fiber-reinforced layer of carbon fiber-epoxy resin, poroelastic layer of sandstone and a viscoelastic half-space.

Optimized determination of elastic constants of crystals and their uncertainties from surface Brillouin scattering

Surface Brillouin scattering of light allows the angular-dependent velocities of Rayleigh surface acoustic waves (SAW), pseudo-SAW and longitudinal lateral waves (L) on the surface of an opaque crystal to be measured, and the elastic constants thereby determined. Closed form expressions exist for the surface wave velocities in high symmetry directions on crystallographic symmetry planes, and these have been exploited in the past for obtaining the values of the elastic constants. This paper describes a procedure for obtaining an optimized set of elastic constants from SAW, pseudo-SAW and L velocities measured in arbitrary directions in the (001) and (110) surfaces of cubic crystals. It does so by affecting a linearization of the numerically determined angular-dependent SAW and pseudo-SAW velocities near the best fit, and using analytic expressions for the L velocity. The method also generates covariance ellipsoids, from which the uncertainties in the determined values of the elastic constants can be read off. The method is illustrated using surface Brillouin scattering data to obtain the room-temperature elastic constants C11, C12 and C44 of the cubic crystals VC0.75 and Rh3Nb.

Effect of reinforcement, gravity and liquid loading on Rayleigh-type wave propagation

In the present time, self-reinforced materials are the basic requirement for civil engineering construction. These constructions encounter surface wave propagation during earthquakes and similar disturbances. Therefore, the study of surface wave propagation in such material is of great significance. The present paper, in the light of practical situation like dams, canals etc. aims to study the effect of gravity on the propagation of Rayleigh-type surface wave in a self-reinforced semi-infinite medium bounded and loaded by an inviscid liquid layer. Secular equation for the propagation of Rayleigh-type wave has been derived in closed form. The effect of gravity, reinforcement and liquid loading on phase velocity of Rayleigh-type wave has been distinctly observed. Numerical computation has been carried out and graphical illustration is provided for analysis of the presented study. Moreover, the effect of reinforced semi-infinite medium is compared to the effect of reinforced free semi-infinite medium on the phase velocity of Rayleigh-type surface wave to unravel the reinforcement effect. The effect of presence and absence of liquid loading on self-reinforced semi-infinite medium for Rayleigh-type wave propagation is also analysed and depicted by means of graphs.

On the reliability and limitations of the SPAC method with a directional wavefield

The spatial autocorrelation (SPAC) method is one of the most efficient ways to extract phase velocities of surface waves from ambient seismic noise. Most studies apply the method based on the assumption that the wavefield of ambient noise is diffuse. However, the actual distribution of sources is neither diffuse nor stationary. In this study, we examined the reliability and limitations of the SPAC method with a directional wavefield. We calculated the SPAC coefficients and phase velocities from a directional wavefield for a four-layer model and characterized the limitations of the SPAC. We then applied the SPAC method to real data in Karamay, China. Our results show that, 1) the SPAC method can accurately measure surface wave phase velocities from a square array with a directional wavefield down to a wavelength of twice the shortest interstation distance; and 2) phase velocities obtained from real data by the SPAC method are stable and reliable, which demonstrates that this method can be applied to measure phase velocities in a square array with a directional wavefield.

Single crystal elastic constants evaluated with surface acoustic waves generated and detected by lasers within polycrystalline steel samples

We report on a laser generated and detected surface acoustic wave method for evaluating the elastic constants of micro-crystals composing polycrystalline steel. The method is based on the measurement of surface wave velocities in many micro-crystals oriented randomly relative to both the wave propagation direction and the sample surface. The surface wave velocity distribution is obtained experimentally thanks to the scanning potentiality of the method and is then compared to the theoretical one. The inverse problem can then be solved, leading to the determination of three elastic constants of the cubic symmetry micro-crystals. Extensions of the method to the characterization of texture, preferential orientation of micro-crystals or welds could be foreseen.

Effect of Rigid Boundary on the Propagation of Torsional Surface Waves in Initially Stressed Gravitating Dry Sandy Medium

The paper aims to study, the effect of rigid boundary on the propagation of torsional surface waves in initially stressed gravitating dry sandy half space. The mathematical analysis of the problem has been dealt with the Whittaker function. Assuming the expansion of the Whittaker function up to linear term, it is concluded that the gravity field will always allow torsional waves to propagate. The expansion of the Whittaker function up to quadratic terms shows two such wave fronts may exist in the medium. Finally, it is concluded that the sandy medium without support of a gravity field cannot allow the propagation of torsional surface waves, where as the presence of gravity field always supports the propagation of torsional surface waves regardless of whether the medium is elastic or dry sandy. Numerical results analyzing the velocity equations are discussed and presented graphically. It has been observed that density, rigidities play an important role for the propagation of torsional surface waves. It has been seen that as the non-homogeneity parameter in the layer increases, the velocity of torsional surface wave also increases. It has also been observed that an increase in compressive initial stresses decreases the velocity of torsional surface wave.

多道瞬态面波评价路桥过渡段填筑质量方法探讨

铁路或公路路基填筑质量评定多引用压实度作为评判指标，但该指标对于填料为级配碎石的路基不适用。本文基于理论推导获得孔隙率和地基系数与面波波速之间的关系式，进而结合采用最小二乘法拟合的现场面波波速探测数据，建立了波速与孔隙率、地基系数之间的关系，并通过与室内外实验得出的二者的标定曲线对比，提出了一种对级配碎石填料路桥过渡段进行填筑质量评估分析的方法。 Compaction degree is always used as the evaluation index in the quality evaluation of the filling quality of railway or highway subgrade. But this index is not suitable for the roadbed which is made of graded crushed stone. Based on the theoretical derivation, the relationship between the porosity, the coefficient of the subgrade and the surface wave velocity is deducted in this paper. And thus a function that describes the relationship between the wave velocity, the porosity and the coefficient of the subgrade was proposed by combining the least square method with the measured data of surface wave velocity. And through the contrast between the indoor and outdoor calibration curve, a method for analysis of the quality of roadbed which is made of graded crushed stone in road and bridge transition section is put forward.

Effect of Gravity and Magnetism on Surface Wave Propagation in Heterogeneous Earth Crust

This paper aims to study the propagation of surface wave in two initially stressed heterogeneous magnetoelastic transversely isotropic media lying over a transversely isotropic half-space under the action of gravity. Heterogeneities of both the layers are caused due to exponential variation in elastic parameters. Dispersion relation is obtained in closed form by using Whittaker's asymptotic expansion. Magnetoelastic coupling parameters, heterogeneity, horizontal compressive initial stress and gravity parameters have remarkable effect on the phase velocity of surface wave. The obtained dispersion relation is found to be in well agreement with the classical Love-wave equation. Comparative study and graphical illustration has been made to exhibit the outcomes.

Korelasi Empirik antara Kecepatan Gelombang Permukaan terhadap Kepadatan dan Kekakuan pada Campuran Laston – WC

Density and stiffness of asphaltic mixture are important parameter used for pavement design and construction. These parameter measure the required thickness of pavement.The aim of this study is to investigate the empirical relationship between pavement density and stiffness of Asphalt Concrete-Wearing Course (AC-WC) and surface wave velocity. Surface wave velocity is obtained from the seismic test set up in laboratory. A high frequency of impact source is employed in order to produce the high frequency waves propagating in mixture samples.The wave displacement is measured by accelerometer receivers connected to the computer for signal processing and spectrum analysis. In this study, AC-WC mixture is prepared with 35×,50×, 75× and 100× blows for providing sample with different density. From the results, it shows that the surface wave velocity is able to detect the various density of samples. Higher density of sample produces higher velocity and vice versa. Some empirical correlations between surface wave velocity with density and stiffness are also produced with significant statistical measures. This study shows the surface wave velocity is potential parameter employed for mixture assessment in pavement design and evaluation.

Phase velocities of Rayleigh and Love waves in central and northern Europe from automated, broad-band, interstation measurements

The increasingly dense coverage of Europe with broad-band seismic stations makes it possible to image its lithospheric structure in great detail, provided that structural information can be extracted effectively from the very large volumes of data. We develop an automated technique for the measurement of interstation phase velocities of (earthquake-excited) fundamental-mode surface waves in very broad period ranges. We then apply the technique to all available broad-band data from permanent and temporary networks across Europe. In a new implementation of the classical two-station method, Rayleigh and Love dispersion curves are determined by cross-correlation of seismograms from a pair of stations. An elaborate filtering and windowing scheme is employed to enhance the target signal and makes possible a significantly broader frequency band of the measurements, compared to previous implementations of the method. The selection of acceptable phase-velocity measurements for each event is performed in the frequency domain, based on a number of fine-tuned quality criteria including a smoothness requirement. Between 5 and 3000 single-event dispersion measurements are averaged per interstation path in order to obtain robust, broad-band dispersion curves with error estimates. In total, around 63,000 Rayleigh- and 27,500 Love-wave dispersion curves between 10 and 350 s have been determined, with standard deviations lower than 2 per cent and standard errors lower than 0.5 per cent. Comparisons of phase-velocity measurements using events at opposite backazimuths and the examination of the variance of the phase-velocity curves are parts of the quality control. With the automated procedure, large data sets can be consistently and repeatedly measured using varying selection parameters. Comparison of average interstation dispersion curves obtained with different degrees of smoothness shows that rough perturbations do not systematically bias the average dispersion measurement. They can, therefore, be treated as random but they do need to be removed in order to reduce random errors of the measurements. Using our large new data set, we construct phase-velocity maps for central and northern Europe. According to checkerboard tests, the lateral resolution in central Europe is ≤150 km. Comparison of regional surface-wave tomography with independent data on sediment thickness in North-German Basin and Polish Trough confirms the high-resolution potential of our phase-velocity measurements. At longer periods, the structure of the lithosphere and asthenosphere around the Trans-European Suture Zone (TESZ) is seen clearly. The region of the Tornquist-Teisseyre-Zone in the southeast is associated with a stronger lateral contrast in lithospheric thickness, across the TESZ compared to the region across the Sorgenfrei-Tornquist-Zone in the northwest.