1. D. R. Toomey and W. C. Hammond, Department of Geological Sciences, University of Oregon, Eugene, OR 97403, USA.
2. W. S. D. Wilcock, School of Oceanography, University of Washington, Seattle, WA 98195, USA.
3. S. C. Solomon, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
4. J. A. Orcutt, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, USA.