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1 Department of Geology and Geophysics, Grant Institute, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK
2 Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, UK
3 Southampton Oceanography Centre, Southampton, UK
This investigation of valley-wall faulting and its relationship to bathymetry focuses on the first two segments north of the Kane Fracture Zone. The valley-wall faults imaged by deep-towed sidescan sonar show aspects common to continental normal faults, and a similar erosional pattern, from a fresh fault surface, through eroded, talus covered scarps, to scarps draped with pelagic sediments. The first, southernmost segment is a symmetric graben at the segment centre, and an asymmetric half-graben at the northern end. The second, northern segment is an asymmetric half-graben for its entire length. The gross morphology is reflected in the faulting style, with multiple small faults at the symmetric graben, and one or two large faults on the eastern wall, defining the asymmetic half-graben. This difference in faulting style may reflect differences in depth to the brittle-ductile transition, with asymmetry occurring when the brittle-ductile transition is deep and brittle faults can cross the axial valley, locking faults on the other side. A gross estimate of horizontal strain accommodated by the valley-wall faults correlates well with valley-floor bathymetry, suggesting that bathymetric segmentation is partially due to tectonic thinning at segment ends.
