Seismic Anisotropy

thank the sponsors and are grateful for the assistance of many people, particularly the colleagues of Dr. Chesnokov in Moscow. The Journal also had special issues on anisotropy ten years ago (Geophys.J.R.astr.Soc., 49, No.1, 1977), and three years ago (Ge0phys.J. R.astr.Soc., 76, No.1, 1984), which we shall refer to as Issues 1, and 2, respectively. These earlier issues were introduced by "State of the Art" papers (Bamford & Crampin 1977; Crampin et al. 1984a), which reviewed a substantial proportion of the studies of anisotropy over the previous period, as well as reviewing the Proceedings. As was anticipated in the last State of the Art paper, this is no longer a feasible proposition. The increasing interest in anisotropy, and the increasing number of observations of anisotropy means that reviews of the whole field of seismic anisotropy can no longer be confined to a few pages. In any case, such reviews are less useful and rapidly become out of date in a field which is undergoing rapid expansion. These previous issues and their State of the Art papers, together with this present issue, mark stages in a substantial revision of our understanding of the in situ condition of rocks in the Earth. Ten years ago, Issue 1 reported mainly theoretical developments, and the fe