Fig. 14From: High-resolution mini-seismic methods applied in the Mont Terri rock laboratory (Switzerland)Three simplified variants of a borehole wall characterised by radial vp gradients. a Intact borehole wall, no BdZ. b BdZ with positive vp gradient, the most common case, less competent near the borehole wall. c BdZ with negative vp gradient, more competent near the borehole wallBack to article page