海原断裂震间滑动和地震周期变形的GPS研究与构造意义

The Haiyuan fault zone, located at the north-eastern margin of the Tibet plateau, is one of the most important and major fault zones in the Tibet plateau. A quantitative study of the slip rate and strain accumulations of the Haiyuan fault is critical to constrain long-term lithospheric deformation processes, and has important implications of earthquake hazard assessment for the Tibet plateau. There are significant discrepancies of the slip rate estimates for the Haiyuan fault, from different kinds of observations including geodetic and geological measurements. This study analyze the GPS data of “Crustal Movement Observation Network of China” （CMONOC）in order to obtain the reliable interseismic velocity field for the north-eastern part of Tibet plateau. And then analyze the locking distribution and creep rate for different segments and different depths of the Haiyuan fault, based on the elastic dislocation fault model. Besides, taking advantage of the paleoseismic study results and earthquake recurrences of the Haiyuan fault, combined with the consideration of crustal and upper-mantle rheology structure in this region, we will use a viscoelastic dislocation model in order to study the slip rate of the Haiyuan fault and the evolutions of the velocity field. This study will help reveal the effects of earthquake cycle and lithospheric rheology on the estimation of the fault slip rate when using geodetic data, and will also provide clues on the active deformation mode, dynamic mechanism of the Tibet plateau.

海原断裂带位于青藏高原东北缘，是青藏高原北部地区一条重要的活动断裂带，对它的滑动速率、应变积累状态的定量研究对于约束青藏高原岩石圈长期的变形机制和地震危险性评估都有重要意义。此前各类观测资料（包括地质和空间大地测量）估算的海原断裂滑动速率存在不同程度的差异。本研究利用“中国地壳运动观测网络”和“中国大陆构造环境监测网络”的GPS资料，获取青藏高原东北缘长期构造变形的地壳运动速度场，采用弹性负位错模型模拟该地区构造变形，深入研究海原断裂在不同分段、不同深度闭锁分布和蠕滑速率的精细特征及其与周边构造单元的关系；综合考虑该地区地壳、上地幔流变结构，结合古地震、复发周期等地质学结果，研究海原断裂在粘弹性位错模型下的滑动速率和形变场演化规律，揭示岩石圈流变结构和地震周期效应对使用大地测量资料估算海原断裂长期滑动速率的影响，提供青藏高原北部构造变形模式、动力学机制和地震孕育的有关线索。

利用中国地壳运动观测网络和中国大陆构造环境监测网络的1999-2017年的GPS观测资料、采用最新的模型和统一的数据处理策略对其进行精细处理，分离了大震震前、同震与震后等不同地震周期阶段的变形信号，获取了包括海原断裂周边地区的青藏高原东北缘以及整个青藏高原地区的现今三维地壳运动速度场；评估了各GPS站点运动速率的精度及其可靠性；采用跨断层GPS速度剖面方法计算海原断裂带的滑动速率，其中左旋走滑速率约为4-6mm/a，初步结果表明海原断裂带的老虎山段和海原段闭锁程度较低；分析了研究区域应变率场分布的主要特征；采用弹性块体运动学方法对青藏高原及周边地区的GPS观测资料进行了数值模拟，拟合的总体残差约为1.08 mm/a, 与GPS观测精度相当。利用该模型获取了整个青藏高原各构造单元的运动学特征，包括地块的运动速率和断层的滑动速率，并与地质学和大地测量学结果进行了比较。同时，与以往有代表性的各类青藏高原活动地块模型以及地质学约束下的块体模型进行了比较，讨论了相关差异及原因。