Interseismic Strain Along the Northern Edge of Tibet Using SAR Interferometry

利用雷达干涉测量技术，测定了藏北阿尔金、塔格和昆仑断裂系统的现今应变速率。这些断裂系统在亚洲大陆变形动力学中起着关键作用，但其滑动速率和伴生变形仍鲜为人知。目前争论的问题包括印度和亚洲之间的交汇量分别被地壳增厚和大陆块体的侧向挤压所吸收，或整个大陆变形分布的特征。这些问题之所以没有得到解决，是因为对碰撞带目前的运动学知之甚少。此外，藏北地区在1997年和2001年发生了两次大地震，破坏了碰撞带北部目前的震间应变模式。通过对合成孔径雷达(SAR)数据的干涉处理，正在建立活动断裂带地面视线位移的空间连续图。这项研究利用了欧洲航天局自1992年以来获得的涵盖西藏北部地区的广泛的ERS SAR数据档案。按照利用加利福尼亚雷达数据开发的方法，通过基线重新估计程序和数据平均，减少了由于轨道确定和对流层相位传播延迟而造成的数据误差。然后结合视线位移图来约束1997年和2001年地震的长期断层蠕变、同震滑动和震后松弛的变形过程模型。这些资料被用来确定昆仑和阿尔金断裂附近的震间应变分布，与断裂有关的远场滑动速率和速率沿断裂长度的变化，与1997年和2001年地震有关的地表位移，这两次地震之间可能的联系，震后过程对断裂其他部分应变积累的影响。滑移率正在与从地质观察中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.