1. H.-P. Bunge, Institut de Physique du Globe de Paris, Laboratoire de Sismologie, 4 place Jussieu, 75252 Paris Cedex 05, France.
2. M. A. Richards, Department of Geology and Geophysics, University of California, Berkeley, CA 94720, USA.
3. C. Lithgow-Bertelloni, Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
4. J. R. Baumgardner, Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87544, USA.
5. S. P. Grand, Department of Geological Sciences, University of Texas, Austin, TX 78713, USA.