Geological Sciences, University of Oregon, Eugene, OR 97403 United States
GPS, Caltech, Pasadena, CA 91125 United States ;
Geology and ESSIC, University of Maryland, College Park, MD 20742 United States ; Earth and Planetary Sciences, McGill University, Montreal, Que H9X 3V9 Canada ;
Geology and ESSIC, University of Maryland, College Park, MD 20742 United States ;