汶川地震巨型滑坡与断层位错InSAR同震形变场耦合效应研究

The Wenchuan earthquake triggered massive coseismic giant landslides in the Longmenshan mountainous area. The fault dislocation and intense ground motion are the direct causal factor of large scale coseismic landslides. The study on the coupling mechanism between fault dislocation and coseismic landslides is helpful to further understand the geohazard process and provide the tectonic deformation evidence for slope failure triggered by the earthquake. The combination observation methods based on multiple aperture radar interferometry and near-field high-rate GPS are proposed to investigate the coseismic displacement field from the earth crust layering dislocation model. The deformation gradient field can be computed at different directions from the derived displacement field. The sensitivity relationships between landslide motion feature, spatial distribution and coseismic deformation are to be analyzed in the project. The topographic and geological data of the representative coseismic landslides near the Yingxiu-Beichuan fault are to be used to establish the quantitative evaluation model with coseismic dislocation deformation as one of sensitivity factors. The numerical and directional coupling relationships respectively between landslide distribution density and coseismic displacement magnitude, slope failure motion direction and coseismic deformation vectors are to be investigated in the project. This proposal aims to reveal the spatial coupling effect between coseismic giant landslides and fault dislocation deformation and promote the capability of analyzing and evaluating the risk of slope failure triggered by the high magnitude earthquake over the Longmenshan area.

汶川地震触发龙门山大量同震巨型滑坡，发震断层的位错运动是诱发同震巨型滑坡的直接初始驱动因素，探索和阐明地震滑坡与断层位错同震形变场的耦合关系，可为龙门山强震作用下的斜坡失稳分析和灾害预测提供重要的构造形变科学依据。本项目提出基于多孔径InSAR与震时高频GPS联合观测的方法，采用地壳分层弹性位错模型反演近断层连续深度空间的精细同震形变场，计算强地震动在不同深度和方向引发特征各异的三维同震形变梯度，分析地面滑坡运动特征和空间分布格局受断层位错滑移的控制响应关系。采用映秀-北川发震断裂带两侧滑坡区的地形地貌与地质岩性参数，建立断层位错形变作为触发同震巨型滑坡主导敏感因子的定量评估模型，获得滑坡分布密度与同震形变幅值的数值耦合关系，揭示滑坡初始滑动与断层位错滑移的方向耦合效应，促进对龙门山区强震诱发滑坡致灾机理的科学认识与灾害预测能力。

本项目以2008年汶川地震触发的龙门山区地震滑坡为具体研究对象，探索了InSAR与像素偏移量获得汶川地震主断裂带两侧地表形变场的方法，采用频率域滤波法去除像素偏移提取的SAR方位向形变场的电离层影响，开展了汶川地震地表破裂线的影像解译与自动识别，北川-映秀断层的地表破裂长约240 km，灌县-江油断层的地表破裂长约72 km，两条破裂线自南西向北东方向延伸成近似平行展布。联合GPS和InSAR观测的地表形变数据约束反演发震断层映秀-北川断层和彭灌断层的同震滑动分布，联合约束反演的InSAR数据模型残差约为7.1 cm，反演精度得以显著改善。反演结果表明，断层滑动在震源处以逆冲分量为主兼具少量右旋走滑，沿北东向破裂传播，走滑分量逐渐增大，在断层破裂末端的青川区域，滑动基本以右旋走滑分量为主，在都江堰、高川、北川、房石和红光呈现出五个显著的滑动密集区，最大滑动量达10m。采用地理空间统计方法，定量分析了地震滑坡与地形因子（坡度、坡向和高程）、与地表破裂线的空间距离、以及与同震形变场的空间响应关系。结果表明，地形坡度在20-40度区间易发生滑坡，地形坡向为东向与东南向易发育滑坡，高程为1000-2000 m区间为地震滑坡高发区，尤其是1000-1500 m区间易发生大型滑坡；距地表破裂线20 km范围内为地震滑坡高发区，尤其是5 km范围内易发生大型滑坡；断层逆冲运动区域相比于走滑区域更易发育滑坡，InSAR斜距向形变量大于0.6 m的区域为地震滑坡的高发区。项目研究获得了对汶川地震触发同震滑坡的进一步科学认识，为地震巨型滑坡空间影响因子的定量化分析及其风险评估提供基础科学依据。