1. Department of Earth Sciences, University of Southern California, Los Angeles, California, U.S.A.
2. Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes, CNRS, IRD, Gières, France
3. Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, U.S.A.
4. Now at Los Alamos National Laboratory, Sante Fe, New Mexico, U.S.A.
5. Seismological Laboratory, California Institute of Technology, Pasadena, California, U.S.A.