Attenuation of High-Frequency Seismic Waves in Eastern Iran

We investigated the frequency-dependent attenuation of the crust in Eastern Iran by analysis data from 132 local earthquakes having focal depths in the range of 5-25 km. We estimated the quality factor of coda waves ( Q _c) and body waves ( Q _p and Q _s) in the frequency band of 1.5-24 Hz by applying the single backscattering theory of S-coda envelopes and the extended coda-normalization method, respectively. Considering records from recent earthquakes (Rigan M _w 6.5, 2010/12/20, Goharan M _w 6.2, 2013/5/11 and Sirch M _w 5.5, 2013/1/21), the estimated values of Q _c, Q _p and Q _s vary from 151 ± 49, 63 ± 6, and 93 ± 14 at 1.5 Hz to 1,994 ± 124, 945 ± 84 and 1,520 ± 123 at 24 Hz, respectively. The average frequency-dependent relationships ( Q = Q _o f ⁿ ) estimated for the region are Q _c = (108 ± 10) f ^(0.96±0.01), Q _p = (50 ± 5) f ^(1.01±0.04), and Q _s = (75 ± 6) f ^(1.03±0.06). These results evidenced a frequency dependence of the quality factors Q _c, Q _p, and Q _s, 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.