1 Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USA. afu@jsg.utexas.edu.
2 Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Planetary Sciences, University of Science and Technology of China, Hefei, China.
3 Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USA.
4 Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, USA.