1. Assistant Professor, Dept. of Civil and Environmental Engineering, California Polytechnic State Univ., San Luis Obispo, CA 93407 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Berkeley, CA.
3. Researcher, United States Geological Survey, Menlo Park, CA.
4. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Los Angeles, CA.