1. Engineer, Berkshire Hathaway Specialty Insurance, 100 Federal St., Boston, MA 02110 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, 2049 Ghausi Hall, One Shields Ave., Davis, CA 95616.
3. Professor, Dept. of Civil and Environmental Engineering, Blume Earthquake Engineering Center, Stanford Univ., 439 Panama Mall, Bldg. 540, Stanford, CA 94305.