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Figure 1 C – 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).