Propagation Of Love Waves Research Articles

EFFECTS OF THE IRREGULAR UNDERGROUND STRUCTURES OF THE WESTERN EDGE ON SEISMIC MOTION AT THE WESTERN PART IN THE NOBI PLAIN

In this paper, we discuss the propagation process of ground motions generated by two earthquakes through the analysis of seismograms recorded on rock and sediment sites. Significant later phases following the S-wave arrivals in horizontal components often appear in the ground motions recorded in the sedimentary plain. We applied 2-D finite difference method to simulate the later phases during the earthquakes observed at the sediment sites using the subsurface structures derived from the seismic and microtremors prospecting process. The results indicate that when considering basin-excited waves, the characteristics of the simulated waveforms including the later phases display good agreement with the observed seismograms. Moreover, the earthquake motion characteristics were clarified by the propagation process of seismic waves in the western part of Nobi Plain. We also clarified effects of the irregular underground structure on the Basin-Induced Love waves propagation.

Love Waves in Layered Graded Composite Structures with Imperfectly Bonded Interface

AbstractTheoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic solutions for Love waves are obtained. By the interface shear spring model, the dispersion relations for Love waves in layered graded composite structures with rigid, slip, and imperfectly bonded interfaces are given, and the effects of the interface conditions on the phase velocities of Love waves in SiC/Al layered graded composites are discussed. Numerical analysis shows that the phase velocity decreases when the defined flexibility parameter is greater. For the general imperfectly bonded interface, the phase velocity changes in the range of the velocities for the rigid and slip interface conditions.

Love wave propagation in layered magneto-electro-elastic structures with initial stress

An analytical approach is taken to investigate Love wave propagation in layered magneto-electro-elastic structures with initial stress, where a piezomagnetic (piezoelectric) material thin layer is bonded to a semi-infinite piezoelectric (piezomagnetic) substrate. The magneto-electrically open and short conditions are applied to solve the problem. The phase velocity of the Love wave is numerically calculated for the magneto-electrically open and short cases, respectively. The effect of the initial stress on the phase velocity and the magneto-electromechanical coupling factor are studied in detail for piezomagnetic ceramics CoFe2O4 and piezoelectric ceramics BaTiO3. We find that the initial stress has an important effect on the Love wave propagation in layered piezomagnetic/piezoelectric structures.

Note on the propagation of Love waves in a certain type of heterogeneous layer lying on homogeneous medium

Summary It has been shown in this paper that propagation of Love waves is possible in a heterogeneous layer of finite depth lying on a homogeneous half-space, the rigidity and density in the upper layer varying as 1/(1 +αZ) where α is constant and z is the vertical height measured from the common interface. We consider a model Earth consisting of a crust of depth 37.5 km in which the rigidity increases from 2.31 × 1011 to 4.53 × 1011 dyn/cm2, over ultrabasic material of infinite depth, having constant density and constant rigidity 6.47 × 1011 dyn/cm2. The density in the upper layer increases from 1.75 g/cm3 to 3.30 g/cm3 and that in the lower medium is 3.40 g/cm3.

Transverse surface waves on a piezoelectric material carrying a functionally graded layer of finite thickness

The propagation behavior of transverse surface waves (Love waves) in a piezoelectric half space of polarized ceramics carrying a functionally graded material layer is studied from the three-dimensional equations of linear piezoelectricity. The Wentzel–Kramers–Brillouin (WKB) asymptotic technique is adopted for the theoretical derivations of analytical solutions in the functionally graded layer. The dispersion relations of Love wave in the structure are obtained for both electrically open and shorted cases. Firstly, these solutions are used to study effect of the gradient coefficients on the dispersive relations and phase velocities of Love wave propagation. Then influence of the gradient coefficients on the electromechanical coupling factor is discussed in detail. The results reported are meaningful for the design of surface acoustic wave (SAW) devices with high performance.

Propagation of Love waves in a smart functionally graded piezoelectric compositestructure

In this paper, the propagation behavior of Love waves in a smart functionally gradedpiezoelectric structure is analyzed. The smart structure consists of three layers, in whichthe piezoelectric plate serves as the upper layer accompanied by a sandwiched graded layerand a metal substrate. In the graded layer, all the parameters and the elastic modulus arerespectively assumed to vary after two mathematical forms, i.e. an exponential functionand a linear function. The WKB method is adopted to analytically solve thepropagation problem of Love waves for both electrical open and short cases on the freesurface, respectively. The phase velocity curves demonstrate that the numberof modes is greater than in the non-graded layer structure. Furthermore, theinfluence of graded variation on coupled electromechanical factor is presented.

Characteristics of strong ground motion data recorded in the Gubbio sedimentary basin (Central Italy)

Various authors, analysing the set of accelerograms recorded at Gubbio Piana (GBP) (central Italy), have demonstrated that strong amplification occurs at this accelerometric station, which is installed within an alluvial basin. In particular, Ambraseys et al. [(2005a), Bull Earthq Eng 3:1–53; (2005b), Bull Earth Eng 3:55–73] observed that the strong motion peaks at GBP greatly exceed the median values predicted by the attenuation relationships they derived for Europe. In this work, we analyse and discuss some characteristics of the ground motion recorded at the GBP station. We show that the ground motion parameters, such as peak-ground acceleration and peak-ground velocity, are strongly influenced by the presence of locally induced surface waves that produce both a lengthening of the significant shaking duration and an increase in the peak values with respect to a nearby bedrock site. The basin-induced surface waves are observed in the three components of motion and their effects on the peak values are particularly evident in the vertical component. In the frequency domain, the energy of the surface waves is mostly restricted to the frequency band 0.4–0.8 Hz for both the horizontal and vertical components. The horizontal and vertical Fourier amplitudes are also very similar, and this indicates that the H/V spectral ratio technique is not applicable to describing the site response due to the propagation of seismic wave in a complex 2D/3D geological structure. Finally, a preliminary polarization analysis shows that the directions of polarization, as well as the degree of elliptical polarization, exhibit a strong variability with time, that may be related to a complex propagation of Love and Rayleigh waves within the basin.

Off‐Great Circle Propagation of Love Waves in Eastern Qinghai‐Xizang Plateau

AbstractThe data of three‐component digital surface waves from 50 portable seismograph stations located in west Yunnan, China, were collected and analyzed in this study. A frequency domain singular value decomposition method was used for polarization analysis; and the polarizations of intermediate period Love waves traveling through the Qinghai‐Xizang Plateau were calculated and evaluated. The result shows that there are obvious polarization anomalies, which could be due to the lateral heterogeneity of the lower crust and uppermost mantle velocity structure in the wave propagation paths. Besides, theoretical arrival azimuths were computed by using the velocity model from a previous tomographic study. There is a general consistency between the theoretical result and the majority of the observations, though the theoretical anomalies are often smaller than the observations. The result of present study indicates the correctness of our velocity model, as well as the complexity of the lithosphere in this area which is not fully reflected in the model.

Love waves in double porosity media

Based on the control equations for double-porosity media extended from Biot's theory, the propagation of Love waves is discussed in this paper. Dispersion equations of Love waves in double porosity medium are obtained by utilizing the usual assumption of Love waves in elastic solid with the coupling mass coefficient ρ 23 and coupling permeability term k (12) being equal to zero. The dispersion and attenuation properties of Love waves in double porosity medium are analyzed. The approximate limit of the Love wave speed is also given. The effects of fracture porosity and fracture permeability on the behavior of the propagation of Love waves are investigated in detail.

Love Wave Propagation in a Layered Piezoelectric Structure Immersed in a Viscous Fluid

This paper is addressed to the Love wave propagation in a layered piezoelectric structure immersed in a viscous fluid. The layered piezoelectric structure consists of an isotropic layer and a relatively thicker transversely isotropic piezoelectric substrate. The velocity of the Love waves changes due to the presence of the viscous fluid. The exact theory is accurate but not convenient to apply because it is generally difficult to get an explicit relation between the quantities we interest. In this paper, the perturbation approach is applied to obtain the explicit relations for the phase velocity and attenuation of Love waves. The result is useful for the measurement of the viscosity and mass density in Love wave sensors.

Polarization method to detect the co-seismic magnetic oscillations

A method for detecting seismomagnetic signals is considered. These signals are generated during the course of the propagation of surface seismic Love wave from far earthquakes. Magnetic field vector of the seismomagnetic signal rotates counterclockwise and has a circular polarization, which allows us to extract the signal against the background noise. By using the described method of polarization filter the seismomagnetic signals from the earthquake on 4 June 2000 have been detected at two remote magnetic observatories. In the other case, the two signals from the disastrous tsunami 2004 earthquake were detected both for the first arrival of Love wave coming directly from the epicenter along the minor great circle arc, and for the second wave propagating along the major great circle arc.

Propagation of Love Waves in an Inhomogeneous Fluid Saturated Porous Layered Half-Space with Properties Varying Exponentially

Based on Biot's theory for transversely isotropic fluid saturated porous media, the complex dispersion equation for Love waves in a transversely isotropic fluid-saturated porous layered half-space is derived with the consideration of the inhomogeneity of the layer. The equation is solved by an iterative method. Detailed numerical calculation is presented for an inhomogeneous fluid-saturated porous layer overlying a purely elastic half-space. The dispersion and attenuation of Love waves are discussed. In addition, the upper and lower bounds of Love wave speed are also explored.

Experimental Investigation on the Interface Properties Evaluation in Piezoelectric Layered Structures by Love Waves Propagation

The linear ultrasonic technique has been extensively used as a powerful, non-destructive test tool for reliability testing and failure analysis of electronic packaging. This is used most often in the inspection of defects such as delaminations, voids, or cracks through use of a SAM (Scanning Acoustic Microscope). Then, as the reliability level that is required of electronic packaging becomes higher and the thickness of package becomes thinner, the possible defect which needs to be detected becomes smaller. In the conventional SAM, however it is very difficult to detect small defects less than m µ 1 . 0 , such as micro-delaminations. In order to solve such a problem, this paper proposes a nonlinear ultrasonic method, where the nonlinearity caused by the effect of crack-face interactions is considered. The basic concept of this method involves harmonic frequencies that are generated in the transmitted ultrasonic wave due to the partial contact at the interface of micro-delamination. As an evaluation index, the nonlinear parameter dependent on the amplitude of the second order harmonic frequency component is obtained by spectral analysis of the transmitted signal. Experimental results show that the nonlinear parameter has good correlation with the micro-gap and the proposed method can detect the micro-delamination even less than nm 1 .

Propagation behavior of Love waves in a piezoelectric layered structure withinhomogeneous initial stress

For the piezoelectric layer/substrate structure with slowly varying inhomogeneous initialstress in the layer, the influence of the initial stress on the properties of Lovewave propagation is studied. The Wentzel–Kramers–Brillouin (WKB) approximateapproach is adopted for analytical derivations. Numerical results obtained for theBaTiO3 layer/borosilicate glass substrate combination system indicate that, under certainconditions, initial stress in the layer can markedly affect the propagation of the Love wave.The analysis is meaningful for the theoretical analysis and engineering applications of Lovewaves.

Propagation of Love waves in an elastic layer with void pores

The paper presents a study of propagation of Love waves in a poroelastic layer resting over a poro-elastic half-space. Pores contain nothing of mechanical or energetic significance. The study reveals that such a medium transmits two types of love waves. The first front depends upon the modulus of rigidity of the elastic matrix of the medium and is the same as the love wave in an elastic layer over an elastic half-space. The second front depends upon the change in volume fraction of the pores. As the first front is well-known, the second front has been investigated numerically for different values of void parameters. It is observed that the second front is many times faster than the shear wave in the void medium due to change in volume fraction of the pores and is significant

Love waves propagation in a piezoelectric layered structure with initial stresses

The propagation behavior of Love waves in a piezoelectric layered structure with inhomogeneous initial stress is studied. Solutions of the mechanical displacement and electrical potential function are obtained for the isotropic elastic layer and transversely isotropic piezoelectric substrate, respectively, by solving the coupled electromechanical field equations. Firstly, effects of the inhomogeneous initial stress on the dispersion relations and phase velocity of Love wave propagation are discussed. Then the influence of the initial stress gradient coefficient on the stress, mechanical displacement and electrical potential distribution in the layer and the substrate is investigated in detail. The results reported in this paper are not only meaningful for the design of surface acoustic wave (SAW) devices with high performance, but also effective for evaluating the residual stress distribution in the layered structures.

Influence of Imperfect Interface on the Propagation of Love Waves in Piezoelectric Layered Structures

Layered structures, especially thin film/coating substrate system play important roles in micro-electro-mechanical system (MEMS) and microelectronics packages. Many surface acoustic wave (SAW) devices/sensors adopt the layered structures to achieve high performance that with a piezoelectric layer deposited on the substrate. Recently, much work has been carried out concerning the propagation behavior of surface waves in piezoelectric layered structures, in which the piezoelectric layers are bonded perfectly with the substrate materials. Actually, due to the thermal mismatch, the unavoidable initial stress in the piezoelectric layer and the brittleness nature of piezoelectric ceramics, imperfections exist in the interfaces of these layered structures. Due to the penetration properties of surface waves, the imperfect interfaces may influence the propagation behavior of surface waves. Up to now, little attention has been paid to the propagation behavior of surface waves in layered piezoelectric structures that the imperfect interfaces are taken into account. The propagation behavior of Love waves in a piezoelectric layered structure with imperfect interface is taken into account. Solutions of the mechanical displacement and electrical potential function are obtained for the piezoelectric layer and substrate, respectively, by solving the coupled electromechanical field equations. Effect of imperfect interface on the phase velocity of Love wave propagation is discussed in detail. Results obtained indicate that imperfect interface can greatly influence the propagation of Love waves under some certain conditions. The potential application of these results in the field of mechanical behavior of materials is also shown.

One mechanism for generation of the co-seismic electromagnetic oscillations

The paper deals with the problem of electromagnetic pulses, which are generated in the earthquake centre at the very moment of main shock, and the co-seismic magnetic oscillations accompanying the propagation of the Love waves far away from the epicentre. The generation of electromagnetic signals under the action of acceleration of the rocks is inertial mechanism in the Earth's crust, which is also known as the Tolman–Stewart effect. Theoretical investigations for excitation of magnetic oscillations by mechanical motion in the earthquake centre are considered, and we have analysed the 1D and 2D models. Using those models we interpret the magnetic signal associated with the M=7.2 earthquake on January 17, 1995. The detection of magnetic oscillations accompanying the propagation of surface Love wave after the strong earthquake far away from the epicentre gives one further argument in support of the hypothesis on the inertial mechanism operating in the Earth's crust. We examine the data of seismic station Talaya and magnetic observatory Mondy located in East Siberia.

3-D wave simulation in anelastic media using the Kelvin–Voigt constitutive equation

We design a numerical algorithm for wave simulation in anelastic media in the presence of free surface, which can be used to model seismic waves at the Earth's surface and ultrasonic waves in heterogeneous materials. The stress–strain relation is based on the Kelvin–Voigt mechanical model, which has the advantage of not requiring additional field variables. The model requires two anelastic parameters and twice the spatial derivatives of the lossless case. The high-frequency components of the wave field are more attenuated than the low-frequency components, with the attenuation factors being approximately proportional to the square of the frequency. The modeling simulates 3-D waves by using the Fourier and Chebyshev methods to compute the spatial derivatives along the horizontal and vertical directions, respectively. We stretch the mesh in the vertical direction to increase the minimum grid spacing and reduce the computational cost. Instabilities of the Chebyshev differential operator due to the implementation of the free-surface boundary conditions are solved with a characteristic approach, where the characteristic variables are evaluated at the source central frequency. The results of the modeling are verified by comparisons to the analytical solutions for Lamb's problem and propagation in unbounded homogeneous media. Examples illustrating the propagation of Rayleigh and Love waves are presented.

On the Propagation of Love Waves in Anisotropic Elastic Media

The Love waves concentrated near the surface of an anisotropic elastic body are studied. A uniform asymptotics of the wave field is constructed with the use of the nonstationary caustic expansion (Yu. A. Kravtsov's ansatz) in the form of a space-time ray series. Using three types of waves, which propagate along any direction in an elastic medium, as a vector basis, sufficient conditions for the existence of a nonzero asymptotic solution of the problem under study are obtained. The procedure for constructing asymptotic series is illustrated with the model of a transversely isotropic medium. Bibliography: 9 titles.