ORTHORHOMBIC MEDIA - MODELING ELASTIC-WAVE BEHAVIOR IN A VERTICALLY FRACTURED EARTH

Vertical fractures and horizontal fine layering combine to farm a long -wavelength equivalent orthorhombic medium. Such media constitute a su bset of the set of all orthorhombic media. Orthorhombic elastic symmet ry is the lowest symmetry for which the slowness surface (the solution of the Christoffel equation) is bicubic rather than sextic. Various p roperties of orthorhombic media, such as the number and location of co nical points and longitudinal directions, may be derived from the slow ness surface or, because of its bicubic character, the squared slownes s surface, which is a cubic surface. From the occurrence and angular o rientation of some of these distinctive features, conclusions can be d rawn with respect to the properties of the medium and to the parameter s of the assumed underlying causes of the anisotropy. The estimation o f these more subtle properties gains greater importance with the proli feration of multiazimuthal seismic surveys and the ability to drill al ong ever-more complicated 3-D well trajectories.