The principal deformation structures developed in basalts from Site 1155 are fractures and veins. In basalts from Hole 1155A, the total number of fractures + veins recorded per meter of core (N/m) averages 6.5/m (ranging from 1.8 to 10.8/m), which is similar to Sites 1152 and 1154 (6.45 and 6.85/m, respectively). Veins, filled by calcite, clay, or silica (see "Alteration") are developed only in Cores 187-1155A-5R through 7R. The average number of veins per meter of recovered core (vein density) is 2.2/m (ranging from 0 to 4.3/m).
In basalts from Hole 1155B, both fractures and veins are common throughout. The fracture + vein density averages 19.4/m (ranging from 6.7 to 40.2/m), and the vein density averages 12.4/m (ranging from 0 to 30.3/m). Vein widths are mostly <2 mm.