Large Three-component seismic data sets from microseismic and controlled sources in a widespread variety of tectonic and lithologic environments - geothermal, deep crustal, ocean floor, seismotectonic, and sedimentary - have yielded evidence for anisotropic shear wave velocities. The observed effect of anisotropy, called shear wave splitting, is an analog of optical birefringence in calcite, and for the upper crust may be interpreted in terms of a population of oriented vertical microcracks or fractures in the crust. As fracture populations, particularly aligned fracture populations, tend to control hydraulic conductivity in crystalline and sedimentary rock, there is a wide-ranging interest in identifying, interpreting, and modeling the seismic evidence for in situ volumes of aligned fractures. The study and interpretation of oriented crack fracture system in the crust is the principal purpose of the AGU Chapman Conference on Seismic Anisotropy in the Crust to be held at the Lawrence-Berkeley Laboratory, Berkeley, California, May 31 to June 4, 1988.
