HYPERBOLIC TRAVELTIME ANALYSIS OF 1ST ARRIVALS IN AN AZIMUTHALLY ANISOTROPIC MEDIUM - A PHYSICAL MODELING STUDY

Wave propagation in a fractured medium is modeled physically using layers of Plexiglas with thin films of water, held under moderate uniaxial confining pressure. 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 percent. 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, moveout curves are hyperbolic for a surface line oriented parallel to the fractures but are nonhyperbolic for a line oriented perpendicular to the fracture. Q anisotropy is observed in the system, with strongest attenuation on propagation paths perpendicular to the fractures. -Authors