Travel-time variations before and after two major earthquakes derived from active-source seismic data

We obtained travel-time variations of Pg and Sg phases of active-source seismic data by superimposing multiple excitation data of different time periods, which were recorded in the Qilian Mountains. We analyzed the travel-time of the stations near the epicenters before and after the Qilian M(S)5.3 on November 23, 2015 and Menyuan M(S)6. 4 on January 21, 2016, and found obvious travel-time change of the phase. We speculated that this abnormal change is due to variation of the velocity of the source regions. This observation indicates that the active source method may become a new approach to earthquake prediction.