福建水口水库M_L4.8地震序列的精定位及其活动图像分析

High-Resolution Hypocenter Location and Activity Images of the Shuikou Reservoir M_L4.8 Earthquake Sequence in Fujian

应用双差定位法对2008年福建古田水口水库ML4.8地震序列进行重新定位,得到539次地震的相对定位结果,减小了定位误差,得到了较精细的地震活动图像。并结合库区地震构造背景和几个较大地震的震源机制解,对水库诱发地震序列的时空特征进行了讨论。结果表明:①震中活动图像呈现出北西向的条带状分布,分布范围为北西向宽4.5km,北东向宽2.9km;②地震序列在时间进程的发展中,前震主要发生于水库岸边,在余震密集期的地震主要发生于水库水域内,余震衰减后期,地震主要发生于水库岸边,形成了岸边—水域—岸边的迁移过程;③震源深度在北西向剖面显示深度由岸边向水域逐渐加深,在时间上,震源深度经历了深—浅—深的过程。最后结合求解的最大前震和最大余震的震源机制解和当地的地震地质背景资料,推测此次序列的发震构造应为北西向的闽江断裂。

Using the double-difference earthquake location algorithm,we relocated hypocenters of 539 earthquakes for the Shuikou reservoir ML4.8 earthquake sequence in Fujian,reduced the location residuals,obtained the fine earthquake activity images.Spatial and temporal characteristics of the earthquake sequence was discussed.We concluded that： ① Epicenter moving image shows a banded distribution trending north west,4.5 km wide in north-west and 2.9 km wide in north-east;② Foreshocks mainly occurred in the reservoir shore,in the intensive phase,aftershocks occurred mainly in the reservoir waters,the late decay of aftershocks occurred mainly in the reservoir shore,forming a shore-water-shore migration process;③ Focal depth profile of North-West show that the depth from the shore to the water gradually deepened,in time,the focal depth experienced a deep-shallow-deep process.At last,combining the largest foreshock and the largest aftershock focal mechanisms,and the local geological background,we speculated that the seismogenic structure of this sequence should be the Minjiang fault.