Figure 2 – Relationship between slow-S velocity (S₂) and fracture density (FD). As fracture density increases, S₂ velocity decreases. In contrast, fast-S velocity S₁ and P-wave velocity V_P do not change, or change by only minor amounts across blocks A through E. In isotropic blocks A and E, there is no S-wave splitting and only one S-wave velocity V_S. In all blocks (A through E), fast-S velocity = V_S, the velocity in the non-fractured rock. Mineralogy, porosity and pore fluid do not change across the profile. The only Earth properties that vary from block to block are fracture density and orientation.