Figure 1 A – Travel time measurements through a test sample before (bottom four traces) and after (top four traces) cracking the sample to create a propagation medium of quasi-aligned fractures. Confining pressure was varied as labeled between measurements. A principal finding is that P and S₁ react weakly to the presence of fracture (panels a and b), but S₂ reacts strongly (panel c). Modified from Xu and King (1989). next >>>