Radiation of surface Stoneley waves by distributed force sources acting at the solid earth-atmosphere interface

Abstract

UDC 534. 222:550.834 Using the Fourier transform, we find an integral solution describing the excitation of seismoacoustic waves in the solid Earth and the atmosphere by time-dependent forces arbitrarily distributed over the interface between the media. The solid Earth and the atmosphere are modeled by an isotropic solid half-space and a homogeneous gaseous half-space, respectively. Depending on the types of the excited surface and bulk waves, classification of the corresponding force distributions is performed. In the case of harmonic sources, an expression for the period-averaged radiated power of the Stoneley wave is obtained. For arbitrary time dependence of the forces, we find an expression describing the the Stoneley-wave energy radiated during the entire time of the source operation.Studying the relations between wave processes in different (solid and liquid) layers of the Earth and in its atmosphere is one of the most important research fields in geophysics. Seismoacoustic waves in the solid Earth-atmosphere system can be excited by various natural and anthropogenic processes accompanied by intense energy releases. This can be the Earth-surface displacements of different types [1-6], volcanic eruptions [7-9], explosions [10][11][12][13][14], and operation of high-power engineering devices, in particular seismic vibrators [15,16].A practically important problem related to the interaction of different Earth's layers via wave processes is, for example, the excitation of surface waves in the infrasonic frequency range by sources of various physical origin, which act at the interface between the solid Earth and the atmosphere. An increase in the number of studied wave types characterized by different velocities and spatial distributions of the wave fields and the radiated energy offers wider possibilities for remote seismoacoustic monitoring of the sources and the atmospheric parameters. In practice, this is necessary for solving a wide range of problems, in particular those related to the modification of the ionospheric communication channels and earthquake forecasting.Although excitation of surface waves has been attracting much attention of researchers (see, for example, [17-28] and references therein), certain problems related to the excitation and propagation of seismoacoustic waves in semi-infinite media are not sufficiently studied. When considering vibrational excitation of elastic waves, the configuration of the sources was already specified at the stage of the problem formulation [29][30][31][32][33]. The problems of calculation of wave fields and the radiated power for arbitrarily distributed surface sources remain open. Moreover, both in the classical work of G. Lamb [34] and in the further development of this approach, the wave excitation is considered for an elastic medium bordering on free space. Under actual conditions, the solid medium borders on a gas or a liquid, and the wave processes in these media affect the formation of both the directional patterns of the sources and the energy distr...

Excitation of Rayleigh and Stoneley surface acoustic waves by distributed seismic sources

“…If the force sources are located on the interface between the media, when h = 0, then Eqs. (27) and (36)-(39) forψ 1 (k, ω),ψ 3 (k, ω), and A 3 (k, ω) correspond to the results obtained in [7]. If there is no gas above the elastic medium, i.e., ρ 1 = 0, then Eqs.…”

“…A similar expression for W S was earlier obtained in [7]. It should be noted that the expression (see Eq.…”

“…The features of variation in the radiated powers of the surface and leaky waves as functions of the source depth are discussed in [8]. In the present paper, we generalize the results of works [7] and [8] to the case of subsurface and distributed force sources, respectively. The problem of excitation of elastic waves in a homogeneous isotropic solid half-space and the bordering homogeneous gas by the time-dependent forces arbitrarily distributed across a limited-size area, which is parallel to the interface between the two media, is solved in integral form.…”

“…(7), (8), (10), and (12) and the radiation conditions. Since in region II there are waves propagating in both positive and negative directions of the z axis, the potentials for 0 ≤ z ≤ h are written in the form…”

“…A general solution to the problem of excitation of seismoacoustic waves in a homogeneous isotropic solid half-space and the bordering homogeneous gas by the time-dependent forces arbitrarily distributed across the plane interface of these media is obtained in integral form in [7], where the expression for the time-averaged radiated power of the Stoneley wave is found in the case of time-harmonic forces, along with the formula describing the Stoneley-wave energy radiated during the entire time of action of the force sources in the case of their arbitrary time dependence.…”