龙滩水库诱发地震的孔隙压力扩散特征

Pore pressure diffusion characteristics of Longtan reservoir-induced-earthquake

利用孔隙压力扩散机制,分析了广西省龙滩水库与蓄水有关的小震精定位数据,获得了5个分区的流体孔隙压力扩散特征.龙滩水库与蓄水有关的小震活动表现出明显分区现象,使用多源孔隙压力扩散过程触发机理,计算出5个分区流体孔隙压扩散系数值为0.04～0.65 m^2/s.根据5个分区流体孔隙压力扩散程度,将这5区划分为Ⅰ、Ⅱ、Ⅲ三种类型,各类型的流体孔隙压扩散系数分别为0.45～0.65 m^2/s,0.25 m^2/s和0.04～0.08 m^2/s.断裂发育的区域内,地震分布范围较大,地震优势分布方向与断裂一致或相交,而断裂不发育的地块内,地震分布集中,无优势分布方向.各分区岩性的差异与流体孔隙压扩散系数的关系不显著.同时,各分区流体孔隙压力扩散的持续时间和最大扩散距离等均与孔隙压扩散系数的大小具有很好的相关性,第二次蓄水后库区发生的M_L4.2最大水库诱发地震位于流体孔隙压扩散系数最大的Ⅰ区.本项研究对分析解释水库诱发震地震机理,定量评价水库诱发地震的危险性具有一定的参考价值.

We analyzed the precisely relocated microseismic events sequences of Longtan reservoir in Guangxi province. By applying pore pressure diffusion mechanism we identified typical spatiotemporal characteristics of 5 microseismic events swarms. Microseismic events sequences of Longtan reservoir showed obvious partitions characteristics, which can be interpreted by multi- sources triggering the diffusion of pore pressure. By assuming that each swarm was triggered by its own pore pressure source, diffusivities with values between 0.04 m^2/s and 0.65 m^2/s were estimated. Based on the pore pressure diffusion characteristics of different microseismic swarms, the 5 swarms can be divided into 3 types,with diffusivities of 0.45～0.65 m^2/s,0.25 m^2/s, and 0. 04～0. 08 m^2/s, respectively. The 3 types of blocks have obvious structure differences,which are closely related to diffusivity values. Areas with fault structure have larger earthquake distribution,and predominant directions of the earthquake distribution are consistent or intersect with fault lines, while in the area without fault structure, the earthquake distribution is concentrated,without a dominant distribution direction. However, the relationship of lithology of different types and diffusivities is not obvious. At the same time,pore pressure diffusive duration time and the maximum diffusive pressure diffusivity. The biggest which has the biggest diffusivity. reservoir induced earthquake, and distance of different types are well correlated with the pore triggered earthquake of ML4. 2 occurred in the block of type 1 This research may be helpful to the study of the mechanism of to assess the risk of reservoir induced earthquake.