1. Southwest Petroleum University, State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu 610500, China, University of Alberta, Department of Physics, Institute for Geophysical Research, Edmonton, Alberta T6G 2E1, Canada, and China University of Geosciences (Beijing), School of Geophysics and Information Technology, Beijing 100083, China..
2. University of Alberta, Department of Physics, Institute for Geophysical Research, Edmonton, Alberta T6G 2E1, Canada..
3. University of Toronto, Department of Physics, Toronto, Ontario M5S 1A4, Canada..
4. China University of Geosciences (Beijing), School of Geophysics and Information Technology, Beijing 100083, China.(corresponding author).