1. Formerly Virginia Polytechnic Institute and State University, Department of Geosciences, Blacksburg, Virginia 24061; presently University of Texas at Austin, Institute for Geophysics, 4412 Spicewood Springs Road, Building 600, Austin, Texas 78759-8500..
2. Virginia Polytechnic Institute and State University, Department of Geosciences, 4044 Derring Hall, Blacksburg, Virginia 24061..