On surface wave propagation in incompressible, transversely isotropic, pre-stressed elastic half-spaces

2004 ◽  
Vol 42 (10) ◽  
pp. 967-986 ◽  
Author(s):  
Danila A. Prikazchikov ◽  
Graham A. Rogerson
2017 ◽  
Vol 33 (3) ◽  
pp. 303-315 ◽  
Author(s):  
S. Gupta ◽  
N. Bhengra

AbstractThis paper presents the feasibility of torsional surface wave propagation in an anisotropic layer sandwiched between two anisotropic inhomogeneous media. The anisotropy considered in the upper layer and the lower half-space is of transversely isotropic kind while the sandwiched anisotropic layer is a porous layer. The directional rigidities and density have been considered linearly and exponentially varying in the half-space and in the upper layer respectively, while it is taken as a variable in the sandwiched layer. The compact form of dispersion equation governing the propagation of the torsional surface wave has been derived by using the Whittaker function under appropriate boundary conditions. The dispersion of the torsional wave and the effects of inhomogeneity parameters, initial stress and poroelastic constant have been calculated numerically and demonstrated through graphs.


Geophysics ◽  
1995 ◽  
Vol 60 (1) ◽  
pp. 185-190 ◽  
Author(s):  
Chih‐Hsiung Chang ◽  
Gerald H. F. Gardner ◽  
John A. McDonald

Velocity anisotropy of surface‐wave propagation in a transversely isotropic solid has been observed in a laboratory study. In this study, Phenolite™, an electrical insulation material, was used as the transversely isotropic media (TIM), and a vertical seismic profiling (VSP) geometry was used to record seismic arrivals and to separate surface waves from shear waves. Results show that surface waves that propagate with different velocities exist at certain directions.


The treatment of homogeneous plane waves given in part I provides the basis for the detailed study of the nature of surface-wave propagation in transversely isotropic elastic media presented in this paper. The investigation is made within the framework of the existence theorem of Barnett and Lothe and the developments underlying its proof. The paper begins with a survey of this essential theoretical background, outlining in particular the formulation of the secular equation for surface waves in the real form F(v) = 0, F(v) being a nonlinear combination of definite integrals involving the acoustical tensor Q (⋅) and the associated tensor R (⋅,⋅) introduced in part I. The calculation of F(v) for a transversely isotropic elastic material is next undertaken, first, in principle, for an arbitrary orientation of the axis of symmetry, then for the α and β configurations, shown in part I to contain all the exceptional transonic states. In the rest of the paper the determination of F(v) is completed, in closed form, for the α and β configurations and followed in each case by a discussion of the properties of F(v) and illustrative numerical results. This combination of analysis and computation affords a clear understanding of surface-wave behaviour in the exceptional configurations comprising, in the classification of part I, cases 1, 2 and 3. The findings for case 1 exhibit continuous transitions, within the α configurations, between subsonic and supersonic surface-wave propagation. Those for case 3 prove that there are discrete orientations of the axis for which no genuine surface wave can propagate and that this degeneracy typically has a marked influence on surface-wave properties in a sizeable sector of neighbouring β configurations. Neither effect appears in previous accounts of surface-wave propagation in anisotropic elastic media.


It has been noticed in part I that the simplified form of transversely isotropic elasticity obtained by taking the moduli to satisfy the relation c 13 + c 44 = 0 (<=> a 5 = 0) has favourable theoretical features, one of which is the possibility of approaching analytically the limiting case of inextensibility along the axis of symmetry. This advantage is exploited in the present paper. On the basis of the restricted theory the surface-wave function F(v) is calculated in closed form for any orientation of the axis relative to the surface-wave basis. The exceptional configurations classified in part I are then considered. Case 2 is unaffected by the vanishing of a 5 while, as shown in part II, case 3 does not arise. The continuous transition between subsonic and supersonic surface-wave propagation encountered in part II persists under the conditions of case 1 and is displayed here with particular simplicity. The passage to the inextensible limit of F(<v) is immediate and the secular equation for surface waves, derived previously by a purely algebraic method, is retrieved directly. No surface wave exists in the α configurations when the inextensibility constraint applies and, although an exceptional plane wave appears, it can no longer be interpreted as a degenerate form of the subsonic wave which propagates in neighbouring configurations. All the other configurations admit a unique surface wave and this wave is subsonic except, perhaps, in the β = ½π configuration where the possibility of supersonic transmission is retained when a 4 < a 2 . The extension of the existence theorem of Barnett and Lothe to the constrained medium is not straightforward. Part 1 of the theorem fails to hold in the α = ½π configuration and part 2 is not fully effective in the remaining α configurations. The theorem holds good for the other configurations, barring β = ½π, if the degenerate part B e of the slowness surface is ignored in the calculation of the limiting speed v ˆ . In the β =½π configuration the theorem remains valid provided that B e is taken into account in the determination of the transonic state.


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