Reflected-refracted and head sh waves formed on a thin layer that is in welded contact with two elastic half-spaces

The reflection and refraction of SH waves by an elastic layer sandwiched between two elastic half-spaces are studied by using the numerical simulation on the basis of contour integration in the complex plane of the horizontal component of the slowness vector. The propagation of body, channel, head, and screened body waves are simulated in time and spectral domains. The wave fields associated with the propagation in the layer have strong attenuation, provided that the wave length is smaller than the value of the thickness of the layer. The stationary wave field of such waves is of resonance nature. Moreover, the maximum of the modulus of the spectral function is shifted to higher frequences as the epicentric distance increases. Thus, the attenuation of such waves depends on spectral characteristics of a source-receiver system. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 225, 1997, pp. 91–120. Translated by T. N. Surkova.     

Propagation of longitudinal viscoelastic waves in a three-layer medium

The nonstationary problem of propagation of a longitudinal plane one-dimensional stress wave through a plane-parallel viscoelastic layer of finite thickness separating two linear elastic half-spaces with different properties is solved in the linear formulation. A plane wave traveling in one of the half-spaces is normally incident on the boundary of the layer (one-dimensional problem). The field in the other elastic half-space, excited as a result of the multiple reflection of the fronts from the boundaries of the layer, is investigated. Graphs of the small displacements at a given point of the elastic half-space are presented. The solution of the problem is based on the dynamic correspondence principle formulated by Bland [3].Central Scientific-Research Institute of Machine Building, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 151–156, January–February, 1971.     

Motion of a Force Source over an Elastic Surface

The motion of a variable point force P(t) over the free surface of an elastic half-space is investigated with a view toward studying wave processes in an elastic medium. Special attention is given to the determination of surface wavefronts, because the detection of the latter from seismogram data can be utilized to locate the position of a source in space and time. This type of planar problem has been investigated previously, for example, in [1], but the analytical solutions of the problem of a stationary source moving with a constant velocity have been obtained only in the limit t without regard for the transient process of wave propagation.     

Attenuation of the interference slow wave in a cracked layer

The attenuation of the interference slow wave propagating in a cracked fluid-filled layer sandwiched between two elastic half-spaces is evaluated. It is proposed that the attenuation is induced by the inelasticity of the fluid. It is shown that the attenuation of the wave may be very small if the thickness of the layer is much less than the wavelength. This explains the possibility of observing the slow wave in real field seismic experiments. Bibliography: 8 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 250, 1998, pp. 153–160. Translated by P. V. Krauklis.     

Transient analysis of a potential pulse in a piezoelectric (622) crystal plate

Transient analysis of the wave propagation due to an electric potential pulse concentrated at a point on the boundary of an infinite piezoelectric plate of the crystal class (622) resting on an infinite elastic medium is considered. The electric potential is studied for an exponential pulse and step pulse. Numerical results are obtained for theβ-quartz plate that rests on aluminium half-space.     

The influence of a crack in a medium on the interference waves

The interference Kr-waves in an elastic half-space with a crack are considered. The processes of dispersion and attenuation of such waves are described and theoretical seismograms are constructed. A number of frequency and velocity characteristics are discussed, which can help to identify the waves in mining investigations.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Vol. 179, pp. 110–115, 1989.     

Scattering of a plane acoustic wave on a periodic array of piston radiators embedded into a rigid screen

The stationary scattering of a plane acoustic wave on a periodic or a doubly periodic set of piston radiators elastically connected with a rigid screen is considered. The screen separates two half-spaces filled with media possessing different acoustic properties. The model considered takes into account energy losses in the elastic ties between the piston radiators and rigid screen. The problem solution in the case where only one half-space is filled with an acoustic medium is found as a special case. The results of numerically analyzing the reflection coefficients of a plane wave as functions either of the frequency of the incident wave or of the angle of incidence of the plane acoustic wave for different values of the parameters involved are presented. Bibliography: 4 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 230, 1995, pp. 125–137. Translated by G. L. Nikitin.     

Boundary layer method in the problem of far propagation of surface SV-waves

The SV polarized wave field is investigated in an elastic gradient layer of constant width. A point source is situated on the boundary of the layer. Rigid contact conditions are assumed to be valid on the boundary between the layer and an elastic half-space. It is shown that the interference field in the principal approximation far from the source does not depend on the relation between the phase velocity and the transversal and longitudinal velocities in the half-space. Bibliography: 11 titles.     

Attenuating Resonance Modes in a Cylindrical Waveguide Placed in an Elastic Medium

Interference attenuating waves traveling in a cylindrical elastic waveguide, placed in an elastic medium, are considered. The group velocity of these waves is intermediate between that of the P wave and that of the S wave; the phase velocity equals that of the P wave. The frequency of the waves is almost constant and is determined by the requirement of constructive interference. The dispersion and attenuation of these waves are described. Bibliography: 3 titles.     

Equations of an effective model of an anisotropic elastic medium with cracks filled with a fluid

For a periodic layered medium in which every period consists of an elastic anisotropic layer and a fluid homogeneous layer, an effective model is derived by averaging. This model describes wave propagation and has two phases. The equations of this model are deduced in the case of the general anisotropy and in some special cases. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 210, 1994, pp. 175–191. Translated by L. A. Molotkov.     

Nonstationary love waves of the SH-type in an anisotropic elastic medium. A kinematic approach

In this paper, the propagation of Love waves in anisotropic elastic media is studied. These waves are a similar to the transverse surface SH waves in the isotropic case. Necessary conditions for the existence of Love waves of this polarization type near the surface Σ of an anisotropic elastic body are deduced. The algorithm developed here makes it possible to find the direction (s) of transverse surface wave propagation (at every point on the surface Σ). The algorithm employed is illustrated by some special anisotropic cases. The space-time method is used to construct the asymptotics of Love waves for those types of anisotropic media the eikonal equation of which is valid on the surface of an elastic body. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 210, 1994, pp. 262–276 Translated by Z. A. Yanson     

Investigation of the wave field in an effective model of a layered elastic-fluid medium

For a medium that consists of alternating elastic and fluid layers, an effective model is constructed and investigated. This model is a special case of the Biot medium. The wave field is represented as Fourier and Mellin integrals. In the Mellin integral, the contour of integration is replaced by a stationary contour. In the expressions obtained, the order of integration is changed and the inner integral is calculated. The outer integral is equal to two residues. The corresponding poles are roots of two equations of fourth order. These roots lie on the right half-plane and may be complex or real. The representation obtained for the wave field is in agreement with the expressions derived by the Smirnov-Sobolev method. Bibliography: 8 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 332, 2006, pp. 175–192.     

Following screened perturbations in an elastic medium with a thin layer

The result of the calculation of the field of a longitudinal wave which has passed through an elastic layer is studied and the character of the propagation of different phases of this wave is determined.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im V. A. Steklova AN SSSR, Vol. 165, pp. 159–165, 1987.     

Lamb's inverse axially symmetric problem

The problem of restoring the velocity of transversal waves in an elastic half-space by a known wave field on the boundary of a medium is studied. The problem is reduced to a system of “integral” equations similar to the Volterra one. Theorems on existence in the small and on uniqueness of the solution are proved. Bibliography: 5 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 203, 1992, pp. 51–67. Translated by T. N. Surkova.     

The passage of a bending wave through an inhomogeneity in an absolutely rigid rib backing an elastic plate

The wave properties of a system consisting of an elastic plate and an absolutely rigid infinite rib with a defect on a segment are examined. An elastic inclusion and a gap are two kinds of defects under study. The Green's function method is applied to the diffraction problem and transforms it to singular integro-differential equations on an interval. For the case of short defects, the nonresonance and resonance asymptotics of the scattering pattern are obtained. These results show that the coefficient of penetration for a gap is much larger than that for an elastic inclusion if the frequency is nonresonant. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 210. 1994, pp. 22–29. Translated by I. V. Andronov.     

The classical and generalized love problems in a domain of low-frequency interference waves of signal type. I

Low-frequency interference waves propagating through a thin elastic layer, which is in rigid contact with an elastic half-space, are considered. A new method for computing the fields of low-frequency waves suggested by G. I. Petrashen allows us to compute the fields of these waves and to draw some conclusions concerning their behavior. In particular, we may conclude that the thin upper layer significantly distorts a signal sent deep into a medium. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 225, 1996, pp. 5–39. Translated by N. S. Zabavnikova.     

Some new solutions of the problems of wave propagation in a two-layer fluid

We present new analytic solutions of the problem of wave propagation in a continuously stratified fluid in the Boussinesq approximation. We study the propagation of internal waves in an ideal fluid in systems of homogeneous-layer/continuously stratified layer and homogeneous-layer/continuously stratified half-space type. We obtain the dispersion equations and study several limiting cases. Bibliography: 2 titles. Translated fromTeoreticheskaya i Prikladnaya Mekhanika, Vol. 27, 1997, pp. 132–137.     

Vertical oscillations of a circular die on an elastic half-space with a cylindrical cavity

The problem on vertical oscillations of a circular die with a plane base that freely lies on an elastic half-space and contains a cylindrical cavity, whose axis is perpendicular to the plane of the base of the die and passes through its center, is considered. The problem is formulated in the form of paired integral equations that are related to integral Weber transforms. The paired equations are reduced to an equivalent Fredholm equation of the second kind. Some results of numerical calculations of amplitude-frequency characteristics of oscillations of the die are given. A comparative analysis with a known solution of an analogous problem for a continuous elastic half-space is given.Translated from Dinamicheskie Sistemy, No. 8, pp. 30–36, 1989.     

Influence of a Weak Boundary on the Wave Field of an Approaching Source

The response of a weak interface inside an isotropic elastic medium to an approaching source is considered. It is shown that a strong shear wave arises in the wave field reflected at an angle greater than a critical one. Properties of this wave are studied, and theoretical seismograms describing the contribution of all reflected waves to the total field are presented. Bibliography: 19 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 308, 2004, pp. 89–100.     

Comparison of the methods for computing interference elastic wave fields in thin-layered media. 1

A nonstationary problem concerning the propagation of low-frequency waves for a model that consists of a packet of elastic layers lying on an elastic half-space is considered, and exact mathematical solutions in the form of repeated integrals are constructed in three basic forms. It is proved that these solutions satisfy initial conditions. The representation of solutions as a superposition of multiple waves is treated. Bibliography: 6 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 332, 2006, pp. 220–239.