1. PhD Student, Dept. of Earth & Environmental Engineering, Columbia Univ., 918 Mudd Building, New York, NY 10027 (corresponding author). E-mail: tc144@columbia.edu
2. Professor, Dept. of Earth & Environmental Engineering, and Dept. of Earth & Environmental Sciences, Columbia Univ., New York, NY 10027. E-mail schlosser@ldeo.columbia.edu
3. Lecturer, Dept. of Earth & Environmental Sciences, and Research Scientist, Lamont-Doherty Earth Observatory, Columbia Univ., Palisades, New York, NY 10964. E-mail david@ldeo.columbia.edu