利用InSAR观测资料研究2010年玉树地震形变过程

Constrained by the observations, previous studies on the deformation process of the large earthquake focused on the co-seismic deformation. This project will study the process and the mechanism of the pre-seisimc, co-seismic and post-seismic deformation of the 2010 Yushu earthquake using many InSAR observations with high quality. Through analysis on the data from geology, geophysics，SAR coherence map, pixel's offset of SAR amplitude image, et al., we will build the fault model corresponding to every InSAR deformation field, and invert the slip distribution of the co-seismic deformation using the deformation inversion algorithm. Because the signal of the pre-seismic and the post-seismic deformation is very poor, it is very difficult to directly invert the slip distribution using the existing deformation inversion algorithm. We will firstly enhance the deformation signal in the pre-seismic and post-seismic InSAR deformation map, then use the seismic deformation simulator developed by the 3D finite element method to model the InSAR observations, and invert their slip distribution on the fault plane by try and error method. Base on this, this project will study the development process of the 2010 Yushu earthquake fault, and analyze the impact of the fault's geometry and the earth model parameters on the simulated results, and study the constraints on the development of the 2010 Yushu earthquake fault. It is significant to implement this project for revealing the the mechanism of the pre-seismic, cos-seismic and post-seismic deformation process of the large earthquake.

受观测资料限制，目前大地震形变过程研究主要集中于同震形变方面。本项目拟利用大量高质量的InSAR观测资料研究2010年玉树地震震前、同震和震后的形变过程与形变机制。通过分析地质学、地球物理、SAR相干图、SAR强度影像像素偏移等方面的资料，建立每幅SAR形变干涉图所对应的局部断层模型，反演同震形变场并获取其滑移分布。由于大地震震前和震后形变均是弱信号，很难直接采用既有的形变场反演方法来获取滑移分布。申请人和研究小组将对玉树地震震前和震后InSAR观测资料进行信号增强处理，再采用三维有限元地震形变模拟算法模拟InSAR观测，通过试错反演获取震前和震后断层面上的滑移分布。在此基础上，研究2010年玉树地震断层的发展过程，分析地震断层几何参数、地球介质参数等对模拟结果的影响，研究2010年玉树地震断层发展的制约因素。该项目的顺利实施将有助于揭示大地震震前、同震和震后形变所蕴含的物理机制。

2010年玉树地震是汶川地震后的又一次重大地震灾害，共造成两千多人死亡。玉树地震包含两个大地震事件（Mw6.9和Mw6.0级地震），时间间隔约一小时，在地震破裂附近发现了无数的地震鼓包。本项目主要目的是利用InSAR资料研究该地震形变的形成机制。研究结果表明：(1) 两次地震造成了两段地表破裂，中间约有15公里地表未见明显破裂；(2) 震前没有明显的地表形变，表明震前断层处于闭锁状态；(3) 在西北段破裂带上存在小幅度的震后形变。利用地震和大地测量资料，我们建立了发震断层的三维有限元模型并模拟了InSAR观测资料，得到了滑移分布。有限元模拟结果表明：断层几何参数对地表形变分布有明显影响；大量的地震鼓包现象与南东段断层的高倾角有关。