1. Graduate Student Research Assistant, Dept. of Civil and Environmental Engineering, Stanford Univ., Stanford, CA 94305-4020.
2. Project Engineer, Malcolm Pirnie, Inc., Suite 1120, One South Church Ave., Tucson, AZ 85701.
3. Professor, Dept. of Civil Engineering and Engineering Mechanics, Univ. of Arizona, Tucson, AZ 85701.
4. Professor, Dept. of Civil and Environmental Engineering, Stanford Univ., Stanford, CA 94305 (corresponding author).