Affiliation: | Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (Permanent address);Laboratoire de Gkophysique Znterne et Tectonophysique (CNRS U. A. 733), Institut de Recherches Interdisciplinaires de Ge'ologie et Me'canique, Universitk Joseph Fourier, BP 53X, 38041 Grenoble Ce'dex, France and Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK |