1. 1U.S. Geological Survey, Albuquerque Seismological Laboratory, Albuquerque, New Mexico, U.S.A.
2. 2Institut de Physique du Globe de Paris, Paris, France
3. 3Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, U.S.A.
4. 4Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany