1. University of Wyoming, Department of Geology and Geophysics, Post Office Box 3006, Laramie, Wyoming 82071. Emails:
2. Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, Georgia 30332.
3. Formerly University of Texas at Austin, Institute for Geophysics, Austin, Texas 78759‐8345; presently Institute of Geological and Nuclear Sciences, 69 Gracefield Road, P.O. Box 30‐369, Lower Hutt, New Zealand.