عنوان مقاله [English]
The Iranian Plateau, characterized by active faulting, active folding, recent volcanic activities, mountainous terrain, and variable crustal thickness, has been frequently struck by earthquakes resulting in the massive loss of life. Studying the seismic hazard as well as evaluating and predicting the strong ground motions require the knowledge of seismic wave attenuation. The complex structure of the Earth’s medium affects seismic wave propagation. Attenuation quantifies the behavior of the seismic energy propagation in the lithosphere and can be utilized for seismic hazard mitigation. Local seismicity makes a large body of data, which provides a unique opportunity to estimate the seismic attenuation. Data from the strong-motion network installed in Tehran region was used to study the seismicity and the frequency-dependent attenuation of the crust. 22 local accelerograms recorded at 14 stations were utilized for the present study. It is estimated that the quality factor of coda waves (Qc) and shear waves (Qs)in the frequency band of 1.5–24 Hz by applying the single backscattering method of S-coda envelopes and the extended coda normalization method, respectively. The values of Qc and Qs show a dependence on frequency in the range of 1.5–24 Hz for this region.Considering records from Shahr-e Rey earthquake (Ml 4, 1388), the estimated values of Qc and Qs vary from 151 ± 49 and 93 ± 14 at 1.5 Hz to1994 ± 124 and 1520 ± 123 at 24 Hz, respectively. The average frequency-dependent relationships estimated for the region are Qs=(9216)f (0.980.15) and Qc=(114±5)f (1.12±0.04). These results evidenced a frequency dependence of the quality factors Qc and Qs, as commonly observed in tectonically active zones characterized by a high degree of heterogeneity, and the low value of Q indicated an attenuative crust beneath the entire region. The experimental results show that lower Q values can be observed for near main shockepicenter stations and higher Q values for distant stations. The quality factor Q is affected significantly by the presence of cracks, and that Q is sensitive to cracks. The environment of the epicenter is more affected by the released energy, and seismic waves recorded in the near field are propagated in the filled crack area. This paper makes a significant contribution to the understanding of crustal attenuation and provides data to fill an important gap in the knowledge of attenuation in this region.