Affiliation: | School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, European Way, Southampton SO14 3ZH,;UK. E-mail: Cube Geophysics CC, 9 5th;Street, Melville, Johannesburg 2092 South Africa Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge CB3 0EZ,;UK |