1. Unconventional Natural Gas Institute, and State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, No. 18 Fuxue Road, Changping District, Beijing 102249, China, chchao@cup.edu.cn, niu@cup.edu.cn, tangyc@cup.edu.cn, taokai@cup.edu.cn
2. Also at Seismological Laboratory, California Institute of Technology, 1200 E. California Boulevard, MS 252‐21, Pasadena, California 91125‐2100 U.S.A.
3. Also at Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS‐126, Houston, Texas 77005 U.S.A.; niu@rice.edu.