The idea for the workshop sprang from two datasets that were presented in seminars. The first was a remarkable (reversed) profile of crosshole data that Jon Claerbout had got from Western Geophysical. Both the vertical and inline horizontal components were available, and they both showed very clean compressional and shear direct arrivals.
The second set of data was shown by Reinaldo Michelena who had sufficiently processed the data under an isotropic assumption that it had become clear that it was, in fact, anisotropic. That is, that slanting rays were traveling faster than horizontal rays.