1. n. [Formation Evaluation]

A situation in which the formation shear-wave velocity varies azimuthally around the borehole, because unequal stresses in the formation have caused azimuthal variations in the stress concentrations around the borehole. These stress concentrations change the shear-wave speeds in the region surrounding the well from those in the far field, such that a characteristic response is observed in the dispersion of the dipole flexural mode.

See: azimuthal,  flexural mode,  S-wave