浙江珊溪水库库区地震波衰减特征研究

Characteristics of seismic wave attenuation in Shanxi Reservoir area of Zhejiang Province

2002—2007年发生的珊溪水库地震事件是少震、弱震的浙江省区域显著的地震事件.搜集182次ML>2.0地震的近场台站数字地震波形,使用这些波形高信噪比的尾波时间域信号,根据计算尾波Qc(f)值的Sato模型,通过滤波及去除环境噪声,计算了地震波传播路径上的尾波Qc(f)值;拟合Qc(f)值与频率f之间的关系,分析了水库区域地震波衰减的时空特征.根据信噪比及计算要求,从近场9个台站的记录中挑选出641条三分向记录,计算尾波衰减参数,得到尾波Qc(f)与频率f的关系为:Qc(f)=52.19±7.11f0.9221±0.05.结果表明,本区域为低衰减区域.震群活动使区域介质对高频率波衰减趋势性增大.进一步对尾波衰减参数及尾波采样体之间的关系分析发现,该区域存在深部高衰减层.

The earthquakes which occurred from 2002 to 2007 in Shanxi Reser- voir area, Zhejiang Province, are very notable, because the province is not considered prone to earthquakes. We have collected waveform data of 182 ML〉2.0 earthquakes recorded at near-source stations. By using the coda time series with high signal-to-noise ratio and filtering the data to eliminate background noises based on Sato model, the coda Qc （f） was calculated, and the relationship between Qc（f） and frequency （f） was obtained. Then, the characteristics of seismic wave attenuation in the reservoir area were analyzed. 641 three-component records chosen from 9 stations were used for this study. Our result shows that the relationship between the coda Qc （f） and f is： Qc （f） = 52.19± 7. 11f^0.9221±0.05 , suggesting that the study area is a tectonically inactive zone. The attenuation coefficient for high frequency waves increases with seismic activity. Further analysis on the relationship between Qc （f） and sampling depth reveals that high attenuation layers exist deep beneath the study area.