Donald V Helmberger, California Institute of Technology, Pasadena, CA, United States, Voon Hui Lai, California Institute of Technology, Seismological Laboratory, Pasadena, CA, United States, Daoyuan Sun, University of Science and Technology of China, Hefei, China, Wenbo Wu, CalTech Seismological Laboratory, Pasadena, United States, Michael Gurnis, California Institute of Technology, Seismological Laboratory and Division of Geological and Planetary Sciences, Pasadena, CA, United States and Jennifer M Jackson, Caltech, Pasadena, CA, United States