1. Dept. of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA 24061 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, CA 95616.
3. Associate Professor, Dept. of Architecture and Building Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan.
4. Associate Director, Center for Geotechnical Modeling, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, CA 95616.
5. Research Assistant Professor, Dept. of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA 24061.
6. Associate Professor, Institute of Engineering Mechanics, China Earthquake Administration, Harbin 150080, China.