(a) Pre-stack depth migrated MCS image of a Cretaceous inside corner high in the Eastern Central Atlantic with (b) geological interpretation of detachment fault geometry (modified from Ranero & Reston 1999). (c and d) Geophysical indications of active detachment faulting in the TAG segment, 26°N MAR (modified from deMartin et al. 2007). (c) Contoured colour indicates deviation from an average 1-D velocity structure; dots are earthquake hypocentres projected onto this section from an area extending a kilometre either side. Yellow lines are interpreted detachment fault and antithetic normal faults. Thick solid-dashed line is the geometry of the detachment fault shown in (b) with its depth adjusted to match the depth of the termination (intersection of the fault and seafloor, T) of both faults. Note the excellent agreement in fault dip within the upper 2–3 km of the crust. (d) Earthquake epicentres in the TAG segment, the curved pattern of western events is inferred to mark the boundary of the footwall to the detachment. White line locates cross section shown in (c).