Variation of intrinsic and scattering attenuation of seismic waves with depth in the Bam region, East-Central Iran

摘要

The attenuation properties of the lithosphere in the Bam region, East-Central Iran, have been investigated. For this purpose, 42 local earthquakes having focal depths less than 25 km have been used. The quality factor of coda waves (QJ has been estimated using the single back-scattering model. The quality factors Q_p, Q_d (P and direct S-waves) have been estimated using the extended-coda normalization method. Q_i and Q_s (the intrinsic and scattering attenuation parameters) have been estimated for the region. The values of Q_p, Q_d. Q_c. Q_i and Q_s show a dependence on frequency in the range of 1.5-24 Hz for the Bam region. The average frequency-dependent relationships estimated for the region are Q_p=(36±6]f~(10.3±0.06), Q_d=(59±8f~(1.00±0.03), Q_c=(79 + 5)f~(1.01±0.04), Q_s=(131±4}f~(1.01±0.04) and Q_i=(104±6)f~(0.01±0.05). A comparison between Q_i and Q_s shows that intrinsic absorption is predominant over scattering. The variation of Q has also been estimated at different lapse times to observe heterogeneities variation with depth. The variation of Q with frequency and lapse time shows that the lithosphere becomes more homogeneous with depth. The estimated Q_o values at different stations suggest a low value of Q indicating a heterogeneous and attenuative crust beneath the entire region.