2016年阿克陶M_S6.7地震地表破裂特征和帕米尔现代构造应力场初步分析

Surface Rupture Features of the Akto M_S 6.7 Earthquake in 2016 and Modern Tectonic Stress Field of Pamir

帕米尔高原位于地中海-喜马拉雅地震带上,晚新生代以来随着印度板块向欧亚板块持续不断地挤压汇聚,其构造运动是欧亚大陆最强烈的地区。高原腹地发育一系列近SN向正断层,包括近SN向的塔什库尔干正断层所处的帕米尔中部现代区域的构造应力场以EW向水平拉张为主。2016年11月25日发生的阿克陶M_S 6.7级地震的发震构造为塔什库尔干断层分支的NWW向木吉盆地北缘断层,其具有右旋走滑兼正断性质。地震在震中附近产生同震地表形变带,全长约1km,呈近SN-NNE向水平拉伸,发育近EW—NWW向的张裂缝,为地震破裂的产物,张裂缝的最大水平拉伸位移量和最大垂直位移量分别为46cm和16cm。地表破裂带中的NE和NW向张剪裂缝只是连接贯通这些雁列的张裂缝,其水平相对位移量取决于张裂缝的水平拉伸量和张裂缝之间的几何关系。地表形变带表现的拉张性质与帕米尔高原腹地区域现代应力场最大主压应力为垂直向基本一致,可能与深部热物质上涌造成的上地壳拉伸有关。而地表形变带呈近SN向水平拉张,与区域近EW向拉张应力场之间存在显著差异,这可能是木吉盆地北缘右旋走滑正断层阶区局部应力场调整的结果。

The Pamir plateau is located in the Mediterranean-Himalayan seismic zones. In late Cenozoic as Indian plate has continuously subducted with the Eurasian plate, its tectonic movement become the strongest in the Eurasian continent. In the interior of the plateau where are series of near S-N-striking normal faults, including near S-N-striking Taxkorgan fault, the modem tectonic stress field in central Pamir suggests mainly E-W directed extension. The seismogenic structure is the N-W-W-striking northern margin of the Muji basin fault, a branch of the Tashkurgan fault, which is the dextral strike-slip and normal active fault. The coseismic surface deformation zone produced by the Akto Ms 6.7 earthquake is about lkm long, along EW-NWW trending. The horizontally tectonic movement is EW-NWW trending tensile fxactures, which are the main earthquake ruptures. The maximum horizontal displacement is 46cm and the maximum vertical displacement is 16cm. The NE and NW trending shear cracks in the surface rupture zone are only connected to these fissures, and the horizontal relative displacement depends on the geometric relationship of the tensile fractures and horizontal tensile displacement. Extension properties of the surface deformation with maximum vertical principal stress are about in consistent with regional stress in the interior of the Pamir plateau, in which related upwelling hot material may result in the upper crust extending. The surface deformation zone has near S-N directed horizontal extension. Compared with near E-W directed extension in the region stress field, the difference is significant, which may be interpreted to adjust the partial stress field of the step between two dextral strike-slip and normal faults of the northern margin of the Muji basin faults.