1. Institute of Arctic and Alpine Research, University of Colorado
Boulder, CO 80309-0450 USA
behrendj@stripe.colorado.edu
2. United States Geological Survey
Denver, CO 80225, USA
3. University of Texas Institute of Geophysics
Austin, TX 78759-8345, USA
4. Lamont Doherty Earth Observatory, Columbia University
Palisades, N.Y. 10964, USA