广西龙滩水库库区地震尾波衰减特征

按照高信噪比和计算要求，从 2006—2013 年广西龙滩水库地震台网的10个子台记录到的龙滩库区近场数字地震波形中挑选出 3 822 条三分向记录，经滤波和消除环境噪声后，采用Sato单次散射模型，计算了地震波传播路径上的尾波Q （ f ）值，对Q （ f ）与频率f之间的关系进行了拟合，并在此基础上分析讨论了库区尾波衰减的时空特征. 结果显示，龙滩库区总体呈低Q₀值和依赖性指数η较高的特点，这两个参数值均低于浙江珊溪水库，与其地震活动程度高于后者的事实相一致。尾波Q值的空间分布显示，周围小震密集分布的台站和历史地震活跃地区的台站的Q₀值低于相对于周围小震分布稀疏的台站的Q₀值。库区尾波衰减参数与尾波采样体之间的关系显示，采样深度越深，尾波参数Q₀值越低，因此认为该区域可能存在深部高衰减层。衰减参数随时间的变化过程表明，蓄水后地震尾波衰减参数仍主要反映了库区原有地壳内部介质的非均匀性和地震波吸收特性，库区地壳介质特性无显著变化，但局部敏感点有所调整。 

Characteristics of seismic coda attenuation in Longtan reservoir of Guangxi region

This paper firstly selected 3 822 three-component records from 10 stations of Long-tan reservoir seismic network from 2006 to 2013 according to the high signal-to-noise ratio and calculation requirements. Based on the Sato single scattering model, this paper calculated the coda Q（ f ） after filtering the data and eliminating ambient noises, and then obtained the relationship between coda Q（ f ） and frequency f. Finally we anayzed the spatio-temporal characteristics of seismic coda attenuation in the Longtan reservoir area. The results show that the Longtan reservoir area is characterized by low Q₀ and high dependence index η, and its Q₀ value and dependence index η are lower than that of Shanxi Reservoir, which is consistent with the fact that the its seismic activity is higher than the latter. The spatial distribution of the coda Q value shows that Q₀ values of the stations with surrounding small earthquakes densely distributed and the stations in the areas with active historical earthquakes are lower than those of the stations with sparse distribution of surrounding small earthquakes. Further analyses on the relationship between attenuation parameters and sampling depth of the reservoir area suggest that there exist deep high attenuation layers beneath the studied area. By analyzing the change process of attenuation parameters with time, it is considered that after reservoir impoundment the coda attenuation parameters still mainly reflect the non-uniformity of the original crustal internal medium of the reservoir area, and the properties of the crustal medium have not been changed significantly, but some local sensitive points have been adjusted.