Reflection Shear-Wave Data Along the Principal Axes of Aximuthal Anisotropy

Heloise B. Lynn, Leon A. Thomsen

This paper presents reflection P and SH field data, collected along two lines, lying approximately parallel and perpendicular to a major oriented vertical fracture set. In the vicinity of the tie point, these data demonstrate the effects of azimuthal anisotropy, i.e., that shear velocity is a function of polarization azimuth. Although the P-wave lines tie, the SH lines do not. One line shows progressive (time-variant) time delays of the shear-wave reflection arrivals, relative to the corresponding arrivals on the other line. Also, for some reflection events, there is a marked difference in shear-wave reflection amplitudes on the two lines. These features are consistent with those expected to result from the known fracture sets. To our knowledge, this is the first publishe seismic reflection field data which show, and in which are recognized, these effects of azimuthal anisotropy. The effects of anisotropy are particularly clear because the lines lie approximately along the principal axes of the anisotropy, so that the effects of shear-wave splitting are minimized.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.