水电工程对断层活动习性的影响及其水库诱发地震效应定量研究

The behavior of fault activity in reservoir area is very special because of the impact of impounding and it is the key factor to control the induced seismicity risk. In this proposal, we integrate seismology and geology investigation with mechanics analysis together to study the behavior of fault activity in reservoir, which is a cross topic of hydropower engineering and active tectonics. After building the geometrical model, physical model and mechanical model, we simulate the stress distribution on the fault resulted from the reservoir impounding by using the three dimensional finite element method and elastic mechanics theory. The stress change and rock property change caused by the reservoir water are respectively analyzed, and the responsive mechanism of fault activity behavior to the reservoir impounding is quantitatively extracted from the viewpoint of mechanical analysis. According to the Navier-Coulomb criteria, we discuss the influences of fault activity behavior change on the condition of fault crack and instability and determine the main controlling factors that impact the fault activity behavior changes caused by reservoir water. Finally, we build the earthquake triggering and delaying mode of fault activity behavior changes and reveal their induced earthquake effect. This proposal is very scientifically significant to promote the theory and method of mechanism research of water induced earthquake based on the fault activity behavior and fault activity behavior research in reservoir area. In addition, this proposal can also provide new theoretical and methodological supports for the prediction and prevention of water induced seismic risk.

水库区断层活动习性受蓄水作用而十分特殊，是决定水库诱发地震危险性的关键因素，是水电工程地质和活动构造领域一个重要交叉研究课题。本项目采用地震地质和力学分析相结合的研究思路，在构建水库几何模型、物理模型和力学模型基础上，根据弹性力学理论，采用三维有限元数值模拟方法，计算水库蓄水前后断层应力状态分布图像，分析水库蓄水导致的断层应力改变和岩石性能改变，从力学分析角度，定量揭示断层活动习性对水库蓄水的响应机制，以Navier-Coulomb破坏准则为判据，探讨断层活动习性改变对断层破坏失稳条件的影响，确定影响蓄水改变断层活动习性的主控因素，建立断层活动习性改变的触震与缓震作用模型，提出断层活动习性改变的水库诱发地震效应。本项目对推进基于断层活动习性的水库诱发地震成因机理以及适应于水库区的断层活动习性研究理论和方法进步具有重大科学意义，并可为发展水库诱发地震危险性预测及风险防控方法提供新的理论支撑。

本项目圆满完成了项目计划书中的各项任务，实现了项目的预期研究目标，在水库蓄水影响断层应力状态改变仿真计算模型及其解算方法、水库蓄水与岩体流固耦合试验模型、水库蓄水在断层上产生的应力改变分布图像及其基本特征、断层活动习性对水库蓄水产生应力改变的力学响应机制、影响水库蓄水改变断层活动习性的主控因素、水库区断层活动习性改变的触震与缓震作用模型、断层活动习性改变的诱发地震效应的预测与防控意义等方面取得了较大进展。项目从几何、物理和力学等方面构建了水库蓄水与岩体流固耦合试验模型，采用有限差分方法，对水库蓄水在不同性质、不同走向、不同倾角和水库不同位置断层上产生的剪应力、正应力和孔隙压力进行了仿真计算，分析和掌握了其基本特征，并从孔隙压力响应和库伦破裂应力变化规律角度，揭示了断层活动习性对水库蓄水的力学响应机制，在此基础上，确定水库蓄水条件、断层性质、断层走向、断层倾角、断层深部岩层的岩性及断层与水库的空间位置关系等是影响断层活动习性改变的主控因素，建立了水库蓄水的触震与缓震作用模型，提出了断层活动习性改变的诱发地震效应，重点构建了水库蓄水对正断层的触震效应、水库蓄水对逆断层的缓震效应以及两种极端条件下水库蓄水的触震与缓震效应等几种诱发地震效应的基本模式，并对基于断层活动习性改变触震与缓震效应的水库诱发地震风险预测与防控方法进行了讨论。这些研究成果不仅对基于断层活动习性改变的水库诱发地震成因机理认识，以及适应于水库区的断层活动习性研究理论和方法具有重大科学意义，而且可以为水库诱发地震危险性预测及风险防控方法提供有价值的理论指导，在水电工程防震减灾和水库除险加固等领域中具有广泛的应用前景。