基于InSAR技术的2016年11月25日西昆仑M_w6.6地震构造变形研究

Tectonic Deformation Study of Nov.25,2016 M_w6.6 Earthquake in West Kunlun Mountain Based on InSAR Technology

采用基于Sentinel-1SAR数据的InSAR技术,对2016年11月25日西昆仑Mw6.6地震从两个角度进行了变形观测,结合构造背景的约束,计算得到了厘米级精度的同震三维变形场,并通过与震源机制解和地表破裂的对比验证了准确性。InSAR变形场为该区同震变形和长期构造活动提供了新的认识:(1)同震变形特征差异显示发震断裂沿西昆仑山南麓展布,走向104°,长度70km,倾向SSE,运动性质为正断滑脱为主兼右旋走滑;(2)同震变形分布范围为100km长×60km宽椭圆形区域,呈现多中心、多方向变形,上盘以下沉为主,最大下沉量10~15cm,水平变形2~6cm,下盘水平运动占主导,滑动量8~14cm为主,垂直变形仅-3~1cm,上下盘整体的垂直变形呈现张压四象限特征,符合走滑剪切作用的结果;(3)地震同震变形具有弹性回跳为主导的变形模式,地区的总体隆升和向北楔入是在长期的区域构造应力场驱动下形成,而局部的特征构造地貌,如断陷盆地和地表破裂,则是同震快速弹性回跳作用的结果;(4)帕米尔高原东北缘长期隆升和本次地震以正断滑脱为主的构造变形现象印证了木吉盆地(也就是公格尔拉张系)的"同造山拉张"成因模型,而不是喀喇昆仑断裂活动NW向延伸作用的结果。

The deformation of Mw 6.6 Earthquake on Nov. 25, 2016 in West Kunlun Mountain was observed from two directions using by Sentinel-1 SAR data-based InSAR technology. Based on the tectonic background, this study obtained a centimeter-scale 3D deformation field and then verified its accuracy through comparison with surface ruptures and focal mechanism of this earthquake. InSAR-based deformation field provides some recognition for the co-seismic deformation and neo-tectonic movement patterns. （1）The differences of co-seismic deformation manifests the extension of seismogenic fault along the piedmont of West Kunlun mountain, striking 104°, 70km long and dipping SSE, which are characterized by mainly normal slip with dextral strike-slip. （2） The co-seismic deformation covers an elliptic area of about 100 km long and 60 km wide, showing multiple centers and multiple directions, with hanging wall subsiding 10-15 cm, horizontal sliding 2-6 cm, and footwall sliding 8-14 cm and vertical deformation of only-3-1cm. Vertical deformation of hanging wall and footwall presents tensile features of four quadrants, in agreement with results of strike-slip shearing. （3）Co-seismic deformation is dominated by mode of elastic rebound, that is, the long-term tectonic stress was the driver for uplifting and northward intrusion of this region, while the local geomorphologies, i. e. surface rupture and graben basin, were the result of elastic rebound. （4）The persistent uplift in the NE margin of Pamir plateau and structural deformation of normal faulting by this earthquake has confirmed the synorogenic extension model of the Muji basin （i. e. Kougur extension）, rather than the result of NW-trending extension of rightslip Karakoram faulting activity.