四川芦山地震区域构造环境与构造应力场特征

Regional Characteristics of Tectonic Stress Field and Tectonic Setting of Lushan Earthquake in Sichuan

2013年4月20日四川省雅安市芦山县发生Ms7.0级地震,这是继汶川地震后发生在龙门山断裂带上的又一次强震。在介绍芦山地震的基本特征及发震构造环境基础上,利用区域内172个震源机制解资料对区域构造应力场进行了计算,特别对龙门山应力区内各类应力数据的最大主应力方向进行了分析。结果表明:龙门山应力区目前处于近东西向的挤压构造应力环境中;区域最大主应力方向在横向上从巴颜喀拉块体的北东—南西向到龙门山块体的近东西向,再到华南块体的北西西—南东东向,表现为顺时针方向的旋转;区域最大主应力在纵向上从柴达木—秦岭块体的北东东—南西西向到龙门山块体的近东西向,再到川滇块体的北西—南东向,亦表现为顺时针方向的旋转;应力方向在不同块体间的转变,反映了青藏高原东缘巴颜喀拉块体在进行南东向水平运动挤压龙门山地块时,由于受到华南地块特别是四川盆地的强烈阻挡,导致龙门山推覆构造带表现为明显的地壳缩短和山体隆升。

In April 20, 2013, a Ms 7.0 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.