LABORATORY AND NUMERICAL MODELS

Figure  shows the laboratory experimental configuration. The cylinders are cut from a sample of Bakken shale (Vernik and Nur, in press); Figure  shows the shape of qP, qSV, and SH wavefronts emanating from a point source in this shale. The layers shown in Figure  are merely to indicate orientation (the real layers would hopefully be on a much finer scale relative to the size of the core). The aspect ratios of the cores in Figure  are correct (40mm tall and 26mm wide); the disks at the top and bottom of each core show the true relative widths of the P-wave transducers (12mm). The SV and SH transducers are almost twice as wide, 20mm, nearly as wide as the core itself.

In this paper we are interested in showing how anisotropy can effect the direct wave from the source to the receiver transducer. A very simplified model is more than adequate for this purpose. We will not clutter the model by attempting to include the rather complex boundary conditions entailed by tilted-axis anisotropy interacting with a truncated cylindrical surface; we will also keep the model two-dimensional. The elastic constants we used for the numerical simulation are C₁₁ = 20.16, C₃₃ = 11.97, C₅₅ = 4.00, C₆₆ = 6.86, and C₁₃ = 5.51. The density has been normalized out so these are all in units of mm/$\mu$s.