1. School of Earth Sciences, Zhejiang University , 38 Zheda Rd., Hangzhou, Zhejiang 310027, China
2. Department of Earth, Environmental, and Planetary Sciences, Rice University , 6100 Main St., Houston, TX 77005, USA
3. Institut de Physique du Globe de Paris , 75205 Paris Cedex 13, France
4. Lawrence Berkeley National Laboratory , 1 Cyclotron Rd., Berkeley, CA 94720, USA