Abstract: In this paper the authors monitor reservoir media variation with time by using repeated earthquakes, normalize the position of repeated earthquakes by using ray tracing to improve the precision, and also calculate the travel time of Badong repeated earthquakes(M_L≥ 2.0) from May 2004 to October 2009 by using ray tracing.The results indicate the velocity variation of crustal media may be influenced by water load and infiltration of Three Gores Reservoir.

Key words: repeated earthquakes , ray tracing , variation of crustal media , Three Gorges Reservoir , Badong