1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, P. R. China.
2. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
3. Institute of Earth and Environmental Sciences, University Potsdam, 14476 Potsdam, Germany.
4. Chengdu Engineering Corporation, Chengdu 610072, P. R. China.