ODP Leg 196: Deformation and Fluid Flow Processes in the Nankai Trough Accretionary Prism

Figure 15.

RAB images of borehole breakouts (dark low-resistivity parallel lines) at 1-in (shallow), 3-in (medium,) and 5-in (deep) penetration from the borehole, 280-325 mbsf. Breakouts occur ~100 m above the frontal thrust zone within log Unit 2. The high-conductivity breakouts indicate elongation of the borehole in the direction of minimum horizontal compressive stress (2 in this case). The two breakout lines occur opposite each other (~180° apart) in the borehole. The orientation of breakouts (northeast-southwest, or ~220°-230°) is in good agreement with the plate convergence vector of ~310°-315° that would be expected to be in alignment with the maximum compressive stress, 1. Notice that the resistivity of the breakouts increases from the shallow to deep image, suggesting minimal invasion and deformation 5 in away from the borehole.