摘要
In April 20,2013,a Ms7.0 earthquake hitted Lushan county of Ya’an city,Sichuan province,which was another strong earthquake on Longmenshan foreland thrust zone after Wenchuan earthquake.Basic characteristics and seismogenic tectonic setting of Lushan earthquake were introduced,and regional tectonic stress field was calculated by 172 focal mechanism solutions,especially the directions of maximum principal stress were analyzed based on five different kinds of stress data in Longmenshan stress region.The results indicate that the direction of maximum principal stress in Longmenshan stress region is nearly in EW-direction compressional tectonic setting at present;the direction of maximum principal stress is from NE-SW-direction in Bayan Har block to nearly EW-direction in Longmenshan block,and then to NWW-SEE-direction in South China block,showing clockwise rotation from west to east in spatial distribution;the direction of maximum principal stress is from NEE-SWW-direction in Qaidam-Qinling block to nearly EW-direction in Longmenshan block,and then to NW-SE-direction in Chuandian block,also showing clockwise rotation from south to north in spatialdistribution.Transition of stress direction among different blocks indicates that Bayan Har block in the eastern margin of Qinghai-Tibet Plateau moves to the south-east and pushes the Longmenshan block because of the strong stop of Sichuan Basin in South China block,and results in obvious crustal shortening and mountain uplift of Longmenshan foreland thrust zone.