Abstract: Velocity changes before and after the April 11, 2012 Sumatra M_S8.6 earthquake have been inverted by ambient tomography method, using continuous waveform records of 99 stations in Sichuan seismic network and Yunnan seismic network from Jan., to Jun., 2012. The characteristics of seismicity in the Sichuan—Yunnan region are also analyzed during the earthquake. Results show that the velocity from the southern segment of Longmenshan fault to Yuanmou—lvzhijiang fault zone and Anninghe fault zone decreased, while the velocity of both sides increased. At the same time, wave velocity changes have a significant correlation with the changes of seismicity. The wave velocity increased together with the seismicity rate in Ninglang—Muli and Leshan—Yaan regions. Wave velocity decreased from the southern segment of Longmenshan Fault zone to Anninghe Fault zone. The seismicity rate of Anninghe Fault zone was also decreased. These show that the results of the velocity change are credible to some extent.

Key words: Velocity changes, Ambient noise, Seismicity, Sichuan-Yunnan region, The 2012 Sumatra M8.6 earthquake