a: poles of all extension veins measured on borehole optical imaging (n = 500), indicating mostly vertical to subvertical extension fractures, while the girdle distribution suggests superposed axes of deformation; b: analysis of the ≥60° dipping extension fractures (n = 320) indicates three distinct families, corresponding to NNE–SSW extension (red), NNE–SSW compression (black) and NW–SE extension (green).