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

The earthquakes which occurred from 2002 to 2007 in Shanxi Reservoir area, Zhejiang Province, are very notable, because the province is not considered prone to earthquakes. We have collected waveform data of 182 M_L>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 Q_c(f) was calculated, and the relationship between Q_c(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 Q_c(f) and f is: Q_c(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 Q_c(f) and sampling depth reveals that high attenuation layers exist deep beneath the study area.