1. Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena 91125
2. U.S. Steel Research Laboratory, Monroeville, Pennsylvania 15146
3. 959 National Center, U.S. Geological Survey, Reston, Virginia 22092
4. Department of Geology, University of California, Los Angeles 90024
5. Department of Metallurgy and Materials Science, Case Western Reserve University, Cleveland, Ohio 44106