1. Principal, G2D Resources, LLC, 7966 Arjons Dr., Suite 204, San Diego, CA 92126-6361 (corresponding author).
2. Professor of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139-4307.
3. Professor Emeritus of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139-4307.