Interseismic Strain Along the Northern Edge of Tibet Using SAR Interferometry

利用雷达干涉测量技术测定了西藏北部阿尔金断裂带和昆仑断裂带的当前应变速率。这些断裂系统在亚洲大陆的变形动力学中起着关键作用，但它们的滑动速率和相关的变形仍然知之甚少。目前有争议的问题包括印度和亚洲之间各自被地壳增厚和大陆块体的横向挤压吸收的辐合量，或整个大陆变形分布的特征。这些问题尚未解决，因为在碰撞区现今的运动学知识贫乏。此外，西藏北部是1997年和2001年两次大地震的发生地，造成了碰撞带北部当前地震间应变格局的破坏。通过对合成孔径雷达（SAR）数据进行干涉处理，构建了沿活动断裂带地表视线位移的空间连续图。本研究利用了欧洲空间局自1992年以来获得的覆盖藏北地区的ERS SAR数据档案。根据加利福尼亚雷达数据开发的方法，使用基线重新估计程序和数据平均，减少了由于轨道确定不良和对流层相位传播延迟而导致的数据误差。然后结合视线位移图来约束1997年和2001年事件的长期断层蠕变、同震滑动和震后松弛的变形过程模型。利用这些数据确定了昆仑断裂带和阿尔金断裂带附近的震间应变分布、与断裂带有关的远场滑动速率及其沿断裂带长度的变化、与1997年和2001年地震有关的地表位移、这两个事件之间可能的联系、震后过程对断裂带其他部分应变积累的影响。滑移率正在与地质观测推断的长期滑移率进行比较。

The current rate of strain concentrated along the Altyn Tagh and Kunlun fault systems in northern Tibet is being determined using the technique of radar interferometry. These fault systems play a key role in the dynamics of the continental deformation in Asia, yet their slip rate and associated deformation are still poorly known. Currently debated issues include the respective amounts of the convergence between India and Asia that are absorbed by crustal thickening and by lateral extrusion of continental blocks, or the characterization of the distribution of deformation throughout the continent. These issues are unresolved because of the poor knowledge of the present-day kinematics in the collision zone. In addition, northern Tibet has been the locus of two large earthquakes in 1997 and 2001 producing a disruption in the current inter-seismic strain pattern in the northern part of the collision zone.Spatially continuous maps of the line of sight displacement of the ground along active fault zones are being constructed by interferometric processing of synthetic aperture radar (SAR) data. This research exploits the extensive archive of ERS SAR data covering the northern Tibet area that have been acquired by the European Space Agency since 1992. Errors in the data due to poor orbit determination and troposphere phase propagation delay are reduced using a baseline re-estimation procedure and data averaging, following the approach developed with radar data of California. Line of sight displacement maps are then combined to constrain deformation process models of long-term fault creep and of co-seismic slip and post-seismic relaxation for the 1997 and 2001 events. The data are used to determine distribution of inter-seismic strain in the vicinity of the Kunlun and Altyn Tagh faults, far-field slip-rate associated with the faults and variation of rates along the length of the faults, surface displacement associated with the 1997 and 2001 earthquakes, possible linkage between these two events, influence of post-seismic processes on the strain accumulation in other sections of the fault. Slip rates are being compared with long-term rates inferred from geological observations.