Do traveltimes in pulse-transmission experiments yield anisotropic group or phase velocities?

Joe Dellinger and Lev Vernik

Presented at the 62nd annual SEG meeting under the title "Do core-sample measurements record group or phase velocity?", pages 662-665. Appeared in the November 1994 GEOPHYSICS, pages 1774-1779.

© 1994 Joe Dellinger, Lev Vernik, and the SEG

Read just the INTRODUCTION, or see the entire text of the paper in postscript form.

You can also download the LaTeX source, if you prefer.

Figures and captions

Figure 1: (GIF) (PS) Shale cores cut at 0, 90, and 45 degrees (perpendicular, parallel, and at a 45-degree angle to the layering respectively). The disks at the top and bottom of each core show the relative width of the P-wave transducers.

Figure 2: (GIF) (PS) The shapes of qP (outer curve), qSV (inner solid curve), and SH (dotted) wavefronts for the medium used in our numerical model. The 90, 45, and 0-degree labels show the direction of vertical for the corresponding shale-core orientations.

Figure 3: (GIF) (PS) Snapshots demonstrating two "ideal" core-sample experiments. The positions and sizes of the source and receiver transducers are indicated respectively by thick (red) horizontal lines at the bottom and top of the model. Top: a wide-source experiment for measuring vertical phase velocity. Bottom: a point-source to point-receiver experiment for measuring vertical group velocity.

Figure 4: (GIF) (PS) Snapshots showing the behavior of qP-waves in our 90 (top) and 45 (bottom) degree core-sample simulations. The dashed lines show the width of Vernik and Nur's cores; the thick (red) solid lines at the bottom and top show the size and positions of the P-wave source and receiver transducers.

Figure 5: (GIF) (PS) How the recorded signal in the 45-degree P-wave case depends on experimental geometry. In the left subplot the transducer width is fixed at 12 mm while the transducer offset is varied; in the right subplot the transducer offset is fixed at 0 mm while the transducer width is varied. Short horizontal lines mark first-break times.

Figure 6: (GIF) (PS) Snapshots showing the behavior of SH (top) and qSV (bottom) waves in our 45-degree simulation.