丽江-小金河断裂带及周缘应力场动态变化与亚失稳识别

5.12 Wenchuan Ms8.0 earthquake and 4.20 Lushan Ms7.0 earthquake successively occurred in middle section and southern section of Longmenshan fault in 2008 and 2013, respectively. Lijiang-Xiaojinhe fault is located in the extension direction of Longmenshan fault to the southwest. It is one of the important seismic activity zones and tectonic boundary within Sichuan-Yunnan block. The recent seismic activity and deformation observations show that strong earthquake risk of this region is becoming larger. Based on the new progress of experiment research work on the meta-instability stage during fault viscosity sliding,and combined with the actual observations such as seismic network data, leveling survey across fault and GPS observations in Lijiang-Xiaojinhe fault and its surrounding area, this project intends to carry out two aspects of work. On one hand, special fault sliding experiment will be designed according to the geometric shape and the geodynamic setting of Lijiang-Xiaojinhe fault to study the variation features of multi-physical field during the meta-instability stage. As a result, the identification marks of the meta-instability stage based on the stress changing feather can be obtained, which can be compared with actual tectonic stress field. On the other hand, using numerical analysis and 3D no-linear finite element numerical simulation, multi-type observations mentioned above would be collected to track the temporal and spatial variation of the surface deformation and the dynamic stress field of this region during the last twenty years. By combining the experimental results with the actual observation analysis, we can inferred whether the studied region is in the meta-instability stage. This research work can provide important basis for earthquake prediction of this region. The established the identification of meta-instable stress state under complex geometric and tectonic conditions, and the method of combining experiment results with the regional dynamic stress field analysis which based on multi-type actual observations have good application prospects as well.

2008、2013年龙门山断裂带中、南段相继发生汶川8.0级、芦山7.0级地震。丽江-小金河断裂带位于龙门山断裂带向西南的延伸方向，是重要的地震活动带和构造边界带，地震活动与形变观测均显示其强震危险日益迫近。本项目拟在该断裂带及周边区域实施的地震台网、定点跨断层形变和GPS多期复测基础上，结合亚失稳实验研究最新结果开展两方面工作。一是针对该断裂带几何展布和构造运动环境进行多物理场亚失稳实验，获得能够与实际资料对比分析的亚失稳阶段应力场变化与识别标志。二是收集整理多种观测资料，利用数值分析、有限元三维接触非线性模拟等追踪丽江-小金河断裂带及周缘二十年以来地表形变和深部构造应力场的动态演化过程，将实验数据与实地观测结合，得到该区是否处于亚失稳阶段的认识。本项研究可为该区强震预测提供重要依据。建立的复杂构造条件亚失稳识别方法、多类型实测数据的动态应力场研究与实验研究相结合的方法具有很强实用性。

丽江-小金河断裂带是重要的地震活动带和构造边界带，地震活动与形变观测均显示其强震危险日益迫近。断层粘滑失稳实验显示失稳前经历亚失稳阶段，并预示失稳不可逆转。亚失稳阶段多物理场演化特征可为判断实际断层是否即将发生地震提供依据。本项目将实验与野外观测相结合，识别目标断裂带是否处于亚失稳阶段，具有重要的实用价值。.本项目对200公里尺度断层在推挤作用下发生的系列地震进行数值模拟，分析强震前后位移场和应力应变场的演化特征，认识亚失稳阶段演化特点及机制。结合亚失稳阶段多物理场演化的物理实验，将形变运动协同化指标引入模拟结果分析，确定基于野外观测的亚失稳识别方法。收集并整理川滇地区1999年以来的GPS、跨断层基线/水准、大面积精密水准网观测、中小地震记录等资料，计算得到GPS方向角指数、区域水平应变场演化图像、GPS连续观测的区域与断层运动时间序列、跨断层场地基线/水准观测的水平张压/扭错时间序列、累积5年地震矩释放AMR空间扫描和丽江-石棉断裂及周边地震精定位结果等。构建川滇地区有限元接触模型，模拟断层运动与区域应力场变化。.根据丽江-小金河断裂带的区域应力应变场变化特征、断层运动与变化形态，结合亚失稳阶段形变场加速协同化的特征指标，对其地震危险进行判断。结果显示，汶川地震以来，断裂带及周缘应力应变场经历复杂的变化过程，先是挤压增强而后持续拉张。GPS方向指数呈有序-无序动态变化，且有序性逐步增强。位于断裂带南部的丽江、下关、永胜、楚雄、剑川等跨断层形变观测以右旋、张性活动为主，2014年景谷6.6级地震后，右旋张性活动进一步增强。区域运动与断层运动变化与亚失稳阶段协同性变化特征具有类似特点。丽江-小金河断裂带有可能逐步临近亚失稳阶段，需要引起重视。作为项目的补充研究，本项目还开展了门源地震前后青藏高原东北缘主要断裂带运动变化特征与疑似亚失稳阶段识别的研究。