Hyperbolic traveltime analysis of first arrivals in an azimuthally anisotropic medium: a physical model study

Abstract

Wave propagation in a fractured medium is modeled physically using layers of Plexiglas with thin films of water, held under moderate uniaxial confining pres- sure. The system exhibits anisotropy comparable to that of measured earth materials; i.e., shear-wave splitting to waves with 3 percent velocity differences and P-wave directional anisotropy of at least 20 per- cent. SV polarizations demonstrate the concept of the shear-wave window with the conversion of an SV body wave to an internal head wave with P-wave velocity, a head wave which is present in both the fractured medium and the control solid (unfractured) medium. For an azimuthally anisotropic medium, mo- veout curves are hyperbolic for a surface line oriented parallel to the fractures but are nonhyperbolic for a line oriented perpendicular to the fractures. Q anisot- ropy is observed in the system, with strongest attenu- ation on propagation paths perpendicular to the frac- tures