不同时期水库地震活动主要影响因素讨论以三峡库区微震活动为例

摘要/Abstract

摘要： 结合微震活动的流体作用强度检测及孔隙压扩散模拟，讨论了三峡库区不同时期微震活动的主要影响因素。以2008年9月蓄水季为界划分前、后期，前期流体渗透导致的孔隙压力增加，使裂隙或断层面强度降低，是库区微震活动的主要影响因素，这一时期微震频次及ETAS模型参数μ值有起伏地缓慢增大，与库水位加卸载过程关系不明显; 后期由于流体渗透引起的孔隙压力变化趋于零，在新的流体平衡条件下，库水位加卸载过程所导致的裂隙或断层面上的应力变化，成为库区微震活动的主要影响因素，这一时期微震频次及μ值显示出与水位变化明显的关联特征。库区小震震源深度的时间变化支持上述观点。在此基础上，进一步讨论了水库“诱发”和水库“触发”地震的力学差异，认为前者主要缘于流体渗透导致的裂隙或断层面强度的“主动”降低，后者则主要与库水加卸载所导致的裂隙或断层面上应力增强有关。进一步推论认为，流体对小地震“诱发”、“触发”皆可能发生，但中强地震缘于流体“诱发”的可能性非常小，对水库区发生的中强地震，流体仅可能对处于临界状态的断层系统起到“触发”作用。

关键词: 水库“诱发”地震, 水库“触发”地震, 流体渗透, 库水加卸载, 裂隙或断层强度, 应力变化, 三峡水库

Abstract: Combining the quantitative checking results of fluid inducing/triggering seismicity and simulation of pore pressure diffusion, major influence factors of the Three Gorges Reservoir-related seismicity have been studied. For the Three Gorges Reservoir, we separated the time period as two parts divided by Sep. 2008, namely earlier stage and later stage. During the earlier stage, the major influence factor of reservoir-related seismicity is the increment of pore pressure caused by fluid intrusion, which decreases the strength of crack or fault surface. In this stage, both the microseismic frequency and μ value, one of the ETAS model parameters which describing the ability of fluid inducing/triggering seismicity, increase fluctuantly and slowly. And there is no relationship with load and unload process by the reservoir water level. During the late stage, because the variation of pore pressure caused by the fluid intrusion tends to be zero, the stress change in the surface of crack or fault caused by the water load and unload process become the major influencing factor of microseismic activity, and the variation of the microseismic frequency and μ value show an obvious and positive correlation with the water level. The temporal changes of the focal depth support this viewpoint. Mechanical difference between reservoir induced seismicity (RIS) and reservoir triggering seismicity (RTS) is also discussed. We think that RIS is mainly due to the strength decrease of crack or fault surface on its own initiative, and RTS is mainly due to the stress variation in crack or fault surface caused by the water load and unload process. It has been inferred that both fluid ' induced' and ' triggered' are possible for small earthquakes, but it is impossible that an moderate or strong earthquake could be induced by reservoir.

Key words: Fluid intrusion, Load-unload process of reservoir, Strength of crack or fault, Stress change, Reservoir induced seismicity (RIS), Reservoir triggered seismicity (RTS), The Three Gorges Reservoir

中图分类号:

P315.7

蒋海昆, 宋金, 贾若, 曲均浩, 陈亚男. 不同时期水库地震活动主要影响因素讨论以三峡库区微震活动为例[J]. 地震, 2014, 34(1): 13-23.

JIANG Hai-kun, WU Qiong, JIA Ruo, QU Jun-hao, Chen Ya-nan. On the Major Influencing Factors of Reservoir-related Seismicity in Different Stages: the Case of the Three Gorges Reservoir[J]. EARTHQUAKE, 2014, 34(1): 13-23.

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