Orthorhombic anisotropy: A physical seismic modeling study

An industrial laminate, Phenolic CE, is shown to possess seismic anisotropy. This material is composed of laminated sheets of canvas fabric, with an approximately orthogonal weave of fibers, bonded with phenolic resin. It is currently being used in scaled physical modeling studies of anisotropic media at The University of Calgary. Ultrasonic transmission experiments using this material show a directional variation of compressional- and shear-wave velocities and distinct shear-wave birefringence, or splitting. Analysis of group-velocity measurements taken for specific directions of propagation through the material demonstrates that the observed anisotropy is characteristic of orthorhombic symmetry, i.e., that the material has three mutually orthogonal axes of two-fold symmetry. For P waves, the observed anisotropy in symmetry planes varies from 6.3 to 22.4 percent, while for S waves it is observed to vary from 3.5 to 9.6 percent.From the Kelvin-Christoffel equations, which yield phase velocities given a set of stiffness values, expressions are elaborated that yield the stiffnesses of a material given a specified set of group-velocity observations, at least three of which must be for off-symmetry directions.

[1]  K. K. Sekharan,et al.  A physical model study of shear-wave splitting and fracture intensity , 1988 .

[2]  L. Thomsen.  Weak elastic anisotropy , 1986 .

[3]  F. Fedorov.  Theory of Elastic Waves in Crystals , 1968 .

[4]  C. Thomson,et al.  A comment on the form of the geometrical spreading equations, with some numerical examples of seismic ray tracing in inhomogeneous, anisotropic media , 1989 .

[5]  S. Crampin,et al.  Seismic body waves in anisotropic media: Reflection and refraction at a plane interface , 1977 .

[6]  Paul G. Richards,et al.  Quantitative Seismology: Theory and Methods , 1980 .

[7]  R. B. Lindsay,et al.  An Introduction to the Theory of Seismology , 1964 .

[8]  N. Banik.  Velocity anisotropy of shales and depth estimation in the North Sea basin , 1984 .

[9]  L. Nikitin,et al.  Wave propagation in elastic media with stress-induced anisotropy , 1984 .

[10]  S. Crampin,et al.  Shear-wave splitting in cross-hole surveys; modelling , 1989 .

[11]  R. J. Brown,et al.  Scaled physical modelling of anisotropic wave propagation: multioffset profiles over an orthorhombic medium , 1991 .

[12]  Stuart Crampin,et al.  Evaluation of anisotropy by shear‐wave splitting , 1985 .

[13]  S. Crampin.  An introduction to wave propagation in anisotropic media , 1984 .

[14]  G. H. F. Gardner,et al.  Hyperbolic traveltime analysis of first arrivals in an azimuthally anisotropic medium: A physical modeling study , 1990 .

[15]  Donald F. Winterstein,et al.  Velocity anisotropy terminology for geophysicists , 1990 .

[16]  S. Crampin.  SUGGESTIONS FOR A CONSISTENT TERMINOLOGY FOR SEISMIC ANISOTROPY , 1989 .

[17]  Stuart Crampin,et al.  A review of wave motion in anisotropic and cracked elastic-media , 1981 .

[18]  Colin M. Sayers,et al.  Stress-induced ultrasonic wave velocity anisotropy in fractured rock , 1988 .

[19]  N. J. Vlaar.  Ray theory for an anisotropic inhomogeneous elastic medium , 1968 .

[20]  Leon Thomsen,et al.  Reflection seismology over azimuthally anisotropic media , 1988 .

[21]  Klaus Helbig,et al.  Elliptical anisotropy—Its significance and meaning , 1983 .