1. Earth and Environmental Sciences Area Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
2. Center for Agricultural Resources Research Chinese Academy of Sciences Shijiazhuang Hebei 050021 China
3. Noble Research Institute LLC Ardmore OK 73401 USA
4. Dip. di Geoscienze Univ. degli Studi di Padova Padova 35131 Italy
5. Section Geophysics, Institute of Geosciences Univ. of Bonn Bonn 53115 Germany