Abstract: In this paper,we extracted seismic velocity changes associated with the 2014 Ludian M_S6.5 earthquake from ambient noise cross-correlation by using continuous seismic data recorded by 13 seismic stations in the research area. Base on temporal changes of seismic velocity of each seismic station pair,we got the spatial distribution of seismic velocity changes,and found that it has significant regional variation. The great changes are mainly distributed on the zones of Zemuhe fault,Xiaojiang fault and Lianfeng fault. There is a sudden post-seismic velocity drop for the region of the southwest segment of the Lianfeng fault and the northwest segment of the Zemuhe fault,and there is a sudden post-seismic velocity increase for the junctional zone of Zemuhe fault and Xiaojiang fault. We found that post-seismic velocity change and stress change have high consistency in the spatial distribution by comparing the stress accumulation of the main active faults around the Ludian earthquake. And there was a positive correlation between co-seismic velocity change and co-seismic stress change. Therefore,stress change associated with the Ludian earthquake may be the main reason of seismic velocity change. We extracted the co-seismic velocity changes associated with the M_S5.1 Yongshan earthquake of April 5, 2014 by the same method. The result showed that seismic velocity increased in the source area of the Ludian earthquake after the Yongshan earthquake.

Key words: Seismic velocity change, Seismic ambient noise, Stress change, The 2014 Ludian M_S 6.5 earthquake