f Elastic anisotropy due to aligned cracks in porous rock

The theory of the effects of cracks upon acoustic velocity in rock is founded upon the classic paper of Eshelby (1957). The effects of a dilute set of aligned ellipsoidal cracks (cf e.g., Hudson, 1980) are well established, although finite concentrations or crack-shape distributions are problematic (Thomsen, 1986b). Despite a long history, there has been essentially no experimental confirmation of this theory. The difficulty has been in fabricating samples containing cracks of controlled number, location, orientation, shape, and size. The new technique discussed by Rathore, et al. (1991) appears to have solved this problem, at least for cracks in porous rock.