Princeton University, Department of Geosciences, Guyot Hall, Princeton, NJ 08544, United States ; California Institute of Technology, Seismological Laboratory, 1200 E. California Blvd., MC 252-21, Pasadena, CA 91125, United States
Institut de Physique du Globe de Paris, 4 place Jussieu, cedex 05, Paris, 75252, France