1. Department of Earth and Planetary Sciences, Northwestern University, 2145 Sheridan Road, Room F374, Evanston, Illinois 60208 U.S.A., kchao@northwestern.edu
2. Also at Northwestern Institute on Complex Systems, Northwestern University, Evanston, Illinois 60208 U.S.A.
3. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332 U.S.A.
4. Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, ZHS 103, Los Angeles, California 90089 U.S.A.
5. Departamento de Geociencias, Universidad Nacional de Colombia, Cra 30 #45 – 03, Bogotá, Colombia
6. Earthquake Research Institute, University of Tokyo, 1‐1‐1 Yayoi, Bunkyo‐ku, Tokyo 113‐0032, Japan