Affiliation: | University of Cambridge, Department of Earth Sciences, Bullard Laboratories, Madingley Road, Cambridge CB3 OEZ, UK. E-mails:;;CASP, West Building, 181A Huntingdon Road, Cambridge CB3 ODH, UK. E-mail:;Najarian Associates, Suite E. One Industrial Way West, Eatontown, NJ 07724-2255, USA. E-mail: |